Fidue A91 Sirius

Pros: Sound quality, build quality, clarity, accessories, modular cable system, balanced frequency response
Cons: Lipless nozzle, slightly sharp front edge

Picture are default 1200 x 800 resolution - click to view larger images.


My first foray into the world of quality sounding IEMs was with Shures range quite a few years ago – starting with the SE425 and culminating with the SE535LE. From there I first experimented with hybrid IEMs – first T-Peos Altone 200 and Dunu's DN-1000 triple drivers, and shortly afterwards Fidues A83 triple. The A83 mesmerised me, and the sound still captivates me when I get them out from time to time. What impressed me was the big sound – the robustness of the bass, but also the way Fidue approached their mid-range. It was something I hadn't encountered before – undoubtedly coloured and mid-forward, but in a really good way. My one issue with the A83 long term was its longevity (build). I had issues with the connectors – but otherwise it was a great IEM.

So when Fidue approached me about reviewing their flagship (Sirius / A91) I was naturally both intrigued and also hopeful. Could Fidue improve on the A83's signature, and also produce a flagship with genuine build quality?

Fidue Acoustics is a Chinese earphone company founded by Benny Tan (who has more than 20 years design experience – developing earphones for other global branded companies). The name Fidue is simply an acronym of the principle design points that the company strives to implement in their product range


From their website “The guiding principle of FIDUE Acoustics is reproducing original sound accurately, and maintaining clarity, dynamics and natural expression.”

Fidue have a full product catalogue including single dynamic driver IEMs in the budget sub $30 range to hybrids – which now include their new TOTL flagship – the Sirius A91. The can be found at Facebook HERE, or their product range viewed at their website HERE.

The Fidue A91 Sirius that I’m reviewing today was provided to me gratis as a review sample. I have made it clear to Fidue that I still regard any product they send me as their sole property and available for return any time at their request. But I thank them for the ability to continue use of the Fidue A91 for follow up comparisons. I do not make any financial gain from this review – it is has been written simply as my way of providing feedback both to the Head-Fi community and also Fidue themselves.

I have now had the Fidue A91 since late 2016. The retail price at time of review is USD 899, and can be purchased via Penon Audio.

PREAMBLE - 'ABOUT ME'. (or a base-line for interpreting my thoughts and bias)

I'm a 50 year old music lover. I don't say audiophile – I just love my music. Over the last couple of years, I have slowly changed from cheaper listening set-ups to my current set-up. I vary my listening from portables (mostly now from the FiiO X5iii, and iPhone SE) to my desk-top's set-up (PC > USB > iFi iDSD). My main full sized headphones at the time of writing are the Sennheiser HD800S, Sennheiser HD600 & HD630VB, and AKG K553. Most of my portable listening is done with IEMs, and lately it has mainly been with the Jays q-Jays, Alclair Curve2 and Adel U6 (although I am spending more and more time with a pair of FiiL Diva lately). A full list of the gear I have owned (past and present is listed in my Head-Fi profile).

I have very eclectic music tastes listening to a variety from classical/opera and jazz, to grunge and general rock. I listen to a lot of blues, jazz, folk music, classic rock, indie and alternative rock. I am particularly fond of female vocals. I generally tend toward cans that are relatively neutral/balanced, but I do have a fondness for clarity, and suspect I might have slight ‘treble-head’ preferences. I am not treble sensitive (at all), and in the past have really enjoyed headphones like the K701, SR325i, and of course the T1 and DT880. I have a specific sensitivity to the 2-3 kHz frequency area (most humans do) but my sensitivity is particularly strong, and I tend to like a relatively flat mid-range with slight elevation in the upper-mids around this area.

I have extensively tested myself (ABX) and I find aac256 or higher to be completely transparent. I do use exclusively red-book 16/44.1 if space is not an issue. All of my music is legally purchased (mostly CD – the rest FLAC purchased on-line). I tend to be sceptical about audiophile ‘claims’, don’t generally believe in burn-in, have never heard a difference with different cables, and would rather test myself blind on perceived differences. I am not a ‘golden eared listener’. I suffer from mild tinnitus, and at 49, my hearing is less than perfect (it only extends to around 14 kHz nowadays). My usual listening level is around 65-75 dB.

For the purposes of this review - I used the Fidue A91 Sirius straight from the headphone-out socket of most of my portables. I did not generally further amp them (I did test them with my E17K, A5 and IMS HVA), as IMO they do not benefit greatly from additional amplification (YMMV and it may depend on your source). In the time I have spent with the Fidue A91 Sirius, I have noticed no change to the overall sonic presentation (break-in). Time spent now with the A91 Sirius would be easily 200+ hours.

This is a purely subjective review - my gear, my ears, and my experience. Please take it all with a grain of salt - especially if it does not match your own experience.


Front of the retail box Rear of the retail box
The Fidue A91 arrived in an approximately” 134mm x 134mm x 71mm retail box. The retail packaging consists of a printed sleeve over a jewellery box style top opening box. The sleeve carries virtually all exterior print, and is fully printed in Fidues normal black and green colouring. On the front is the Fidue logo, and some information about the Sirius configuration. The rear of the sleeve has specification information and a little blurb to explain the reason for the naming convention of the Sirius:

“Sirius is the brightest star in the universe. The ancient Greeks believed that it was the guardian of the road of the soul and an omnipotent hunter”.

The inner box The A91 Sirius nestled safely in the top tray
The inner box has a textured black outer surface, and simply the words “Fidue Sirius” on the top cover. Opening this reveals the A91 Sirius nestled safely in a foam holder, and a some of the included silicone tips. On the underside of the top tray are further cut-outs, and this houses the modular cable adaptor system. Beneath this is a secondary foam layer – and in this is snuggled the case – which houses the rest of the accessories.

The cable adaptors and manual Bottom layer with storage case
The accessories include:
  • 4 pairs of black silicone tips (XS/S/M/L)
  • 1 pair of medium T500 genuine Comply tips
  • 3.5mm Female to 6.5mm Male Adapter
  • Airline adaptor
  • Anodised aluminium storage case (large)
  • Cleaning tool and disassembly tool
  • Maintenance and warranty card.
  • Fold-out booklet/manual
  • 1 x 2.5 mm balanced to MMCX earphone cable
  • 1 x 2.5 mm balanced to 3.5 mm single ended short adaptor cable
  • 1 x 2.5 mm balanced to 3.5 mm balanced short adaptor cable

The storage caseAccessories inside the storage case
The storage case is pretty large, and realistically won't be used as a carry case – unless in a larger jacket pocket or carry bag. It is 85mm in diameter, 45mm in height, with a lift-off lid, and internally lined with a soft felt like material. It looks pretty classy and is ideal for safe storage on a desk top.

Main cable, standard adaptors, comply tips and toolsThe A91 Sirius, cable adaptors and silicone tips
All in all, the accessory package seems well thought out (although a larger tip selection might have been a good idea), and the included accessories are very good quality.

(From Fidue’s packaging / website)
ModelFidue A91-Sirius
Approx price$899 USD (Penon Audio)
TypeFive driver hybrid IEM
Driver - Dynamic1 x 10mm titanium DD
Driver - BA2 x Knowles dual BA (4 BA)
Freq Range4Hz – 45 kHz
Sensitivity113 dB
Cable1.3m, replaceable (MMCX)
Jack2.5mm rhodium plated balanced, straight – with adaptors
Weight37g with default cable
Casing materialAnodised Steel

The graphs below are generated using the Vibro Veritas coupler and ARTA software. Ken Ball (ALO/Campfire) graciously provided me with measurement data which I have used to recalibrate my Veritas so that it mimics an IEC 711 measurement standard (Ken uses two separate BK ear simulators, we measured the same set of IEMs, and I built my calibration curve from shared data). I do not claim that this data is 100% accurate, but it is very consistent, and is as close as I can get to the IEC 711 standard on my budget.

The graphs are provided merely as a point of discussion, and later in the review I've included comparisons to other IEMs for similar reference.

A91 Sirius frequency and channel matchingA91 Sirius – vent unblocked vs vent blocked
Now the interesting thing with measuring the A91 Sirius is that there is a tiny dynamic driver vent just below the nozzle, and there is quite a big difference between having the vent blocked or fully open. I don't have an actual ear mould when measuring – so my main measurements are with the vent complete unimpeded which may not necessarily be the case when worn. In my own personal opinion, I think the unblocked graph is reasonably accurate – but I do think that there is the possibility of little more bass when worn – just enough to give a very slight natural mid-bass hump, and little more extension to the sub-bass.

My sonic impressions of the A91 Sirius – written well before I measured:
  • Bass performs well (sub and mid-bass), reaches low but is not over-emphasised. There is audible sub-bass rumble, so bass extension appears to be pretty good.
  • Lower mid-range is not recessed at all, and male vocals are well represented.
  • Upper mid-range is emphasised, and it is a definite colouration, but one I appreciate. Female vocals have a wonderful sense of euphony, and the bump gives very good clarity without losing overall tonality
  • Lower treble extension is good – but there appears to be some roll-off above about 7 kHz. Cymbal fundamentals are pretty good – but the decay is ever so slightly truncated (hardly noticeable in most tracks). It does contribute to a clean and clear sound though, and one that is thoroughly enjoyable.
  • Overall a well balanced earphone with an upper mid-emphasis
  • Channel matching is excellent


Internal side of the shellFront (internal) and top
The A91 Sirius is incredibly well built and finished, and definitely worthy of being called Fidues top monitor. The outer shell is metallic grey and utilises stainless steel alloy which I assume will contribute to reduction in harmonic resonance. The shape is almost a half circle (some have described it as a wing design), and it is ergonomically designed to fit in the natural half circle hollow inside your ear's tragus, antitragus, and antihelix.

External side of shellRear and view of sockets
The A91 Sirius is a large IEM with a width of 28mm, height of 18mm and depth of approx 10mm (excluding nozzle). The interior or internal side is beautifully rounded with “almost” no sharp corners or angles. The nozzle sits out and is gently angled up from the main body, protruding just over 5mm in length. It is just under 6mm in diameter, mesh covered and lipless. Below the nozzle is a small bass port – which does have an effect on bass quantity if blocked. Toward the rear is two somewhat larger “vents” and I put these in quotes as I'm not really sure they are simply just decorative. Covering them does not seem to alter the sound. Above this is either an L or R marking the ear designation.

MMCX socket and male connector(right) default cable fully connected, (left) CA Tinsel cable
The exterior or external side has the Fidue logo and the “swept triangular” design which was originally seen on the Fidue A83. There is a thin silver line around the outside which contrasts nicely with the grey and gives the A91 a very classy external look. It is definitely an attractive earphone. One thing to note is that while the rest of the IEM is nicely rounded the top decorative plate is flat and there is a bit of an edge. Also at the very front of the IEM the forward apex or triangle, while rounded, is also quite angled, and combined with the flat top does create some potential edges for some people. More on that later.

Y-split and cinch2.5mm balanced jack
At the top rear is the MMCX socket. It is threaded to further strengthen and maintain connectivity. Anyone with experience of the A83 will know about some of the connection problems Fidue have had in the past with MMCX set-ups, and with the A91 they have come up with a pretty good solution. The male connector has a rotating threaded cap which is used to further secure and protect the connection once it is snapped in place. This also allows the user to tighten it right down and essentially fix an angle for cable exit which can further stabilise the wearing position. The connectors snap together really solidly, and are very difficult to get apart – where is where the included (shaped like a guitar pick) accessory tool comes in. Simply use that to gently lever the two connectors apart once the thread is undone. Fidue's solution is elegant and works incredibly well – I just wish this sort of thing could be standardised across all IEM makers. The other good news with this set-up is that other MMCX cables can also be used – they simply snap in place – albeit at the cost of not having the threaded locking mechanism.

The cable system is heavy duty, modular, and one which will see some people loving it, and others perhaps not so endeared. The main cable is 1.3m long and consists of a very flexible braided 8 core SPC cable which is nylon covered throughout. As such it is extremely strong, and so far for me has been surprisingly hard wearing (I expected some fraying, but so far, so good). It has not been prone to tangling – but is somewhat bulky. So far – hooked over the ear, and worn under and outer layer of clothing, it is quite free of microphonics. The Y-split is the same lightweight metal alloy of the main body, well relieved and has a very good cinch in-built which works really well.

Modular adaptors3.5mm balanced adaptor connected
The 1.3m cable terminates at a straight, very well built jack – rhodium plated, and with excellent strain relief. Again the body is the same metal alloy. What is different with the A91 is that the main cable terminates with a 4 pole 2.5mm balanced TRSS connector. This makes it a perfect accompaniment for my FiiO X5iii or Luxury & Precision L3. However – what about standard 3.5mm TRS connections, or even other balanced connections like the 3.5mm TRSS Hifiman Supermini? Well that is where the included short cable adaptors come in. They convert the 2.5mm balanced to either 3.5mm balanced or 3.5mm SE so can be used with a wide variety of devices. The cables and plugs are the same excellent quality of the main cable, but they do add an extra bulk and about 16cm overall extra length to the cable. Again, the connections are pretty solid, and my one design wish here would have been a slight recession in the sockets of the extension/converters to allow the cables to fully snap together with no gaps.

The A91 Sirius – aesthetically stunningAnd versatile – paired with my iPhone and Bluetooth adaptor
Overall though I can’t fault the overall build quality. Top notch use of materials by Fidue – but there is a minor question in the choice of design for the shell – which we'll cover further in the fit/comfort section


I'll start with the easy one (isolation), and we can then look at fit and comfort. Isolation is dependent on tip selection, and if you get a good seal, it is actually pretty good (about average for a vented hybrid IMO), but will not ultimately reach the high isolation of sealed BA IEMs. It would still be reasonably good for a busy street, or some forms of public transport though – although wouldn't be my personal choice for long haul flights.

Now we get to fit and comfort – and these thoughts are more subjective. As I said above, the Fidue A91 Sirius has an ergonomic body shape, with a good length of slightly angled nozzle, and for me personally they are extremely easy to fit – but the nozzle is relatively shallow in-ear. They are designed for over-ear use. Anyone used to ergonomic BA designs should have no issues. They are also quite comfortable for everyday use …… but with a small note. When I first wore the A91 Sirius I would experience some discomfort with a single sharp edge. It wasn't a huge problem – but I knew it was there. The issue for me was simply that I wasn't use to the the sharper angle reacting with my intertragical notch, and because I have bigger ears, I could feel the flat external edge against my skin. The answer was in my choice of tip (Shure Olives), so I could adjust the A91 Sirius so that the pressure there was relieved. It also took some time for my ear to get used to the angle. Nowadays, I can wear the Sirius for hours – and find it very comfortable. But for Fidue – this may be a point worth noting. Neither would be an issue with some rounding of the juncture of the top external plate, and also a less acute angle at the front. Another thing which may help is an extra couple of mm length on the nozzle.

Spinfits and foam tips fit well – others not so goodMy preferred Shure Olives
Another little gripe and this isn't a huge one because ultimately large Comply, stretched Shure Olives, and the included silicone tips all seem to stay put quite well, but the lack of lip on the nozzle means that some tips I like to have options with simply can't be used (e.g. Spiral-dots or my Sony Isolation tips). The smooth nozzle means that some tip bores won't hold and this limits my options. In this case, there are no tuning filters – so I really can't see why this is missing. Anyway – it's slightly annoying – but alleviated by the fact that there are fortunately a number of tips that do work. I tried and can get successful seals with Ostry tuning tips and Spinfits (although they sometimes both slipped off the nozzle) and also a larger size of Comply tips. Ultimately I ended up going with my pair of “stretched bore” Shure Olives – which always give me best fit, comfort and seal for shallower fitting earphones.

Part of the issue is the lipless nozzleBut fit for me is still pretty good
The Fidue A91 sit nicely flush with my outer ear, and are comfortable to lie down with. I've slept with them often, and now that I am used to the overall shape, have even slept on occasion for a full 8 hours (music very, very low of course) – and with no discomfort on waking.

So the overall build is brilliant, and the design could be improved slightly, but again extremely good and well thought out.


The following is what I hear from the Fidue A91 Sirius. YMMV – and probably will – as my tastes are likely different to yours (read the preamble I gave earlier for a baseline). Most of the testing at this point (unless otherwise stated) was done with my FiiO X5iii (single ended) and also the X3ii + E17K combo, no EQ, and Shure Olive foam tips. I used the FiiO devices simply because paired they give me a very transparent window to the music with low impedance, and more than enough power. With both, their was no DSP engaged.

My trusty FiiO X3ii + E17KAnd the very classy FiiO X5iii
For the record – on most tracks, the volume level on the E17K (paired with X3ii) was around 16/60 (on low gain) which was giving me an average SPL around 65-75 dB. On the X5iii (again low gain), this equated to 29/120 for the same volume. Tracks used were across a variety of genres – and can be viewed in this list

  • Sub-bass – has good extension and even at my low listening levels is audible, but there is no boosted emphasis and it sits extremely well within the overall frequency mix. There is enough rumble to give presence without overshadowing vocals, and I'm detecting no bleed into lower mid-range. Lovers of elevated lower bass frequencies would need to EQ or play with partially blocking the bass port.
  • Mid-bass – pretty linear compared to lower mid-range and to my ears sounds quite natural but with no real emphasis. Slightly more mid-bass than sub-bass, but neither is really emphasised. Any mid-bass hump would be very slight. This reminds me very much of original HD800 type mid-bass – enough to sound tonally natural and give very good overall timbre, but again its relatively linear or flat rather than emphasised.
  • Lower mid-range – no recession compared to bass but quite a bit lower than the upper mid-range peak around 2 kHz (about 10 dB). Vocals don't appear overly distant though, and this is fantastic – especially when you consider the overall cohesion between lower and upper mid-range for vocals. Male vocal in particular have a reasonable amount of body, but there is definitely more emphasis with female vocals.
  • Upper mid-range – elevated compared to lower mid-range, and there is a rise from 1 kHz to the main peak at 2 kHz. The result is a clean and clear vocal range, with extremely good overall cohesion and some real euphony for female vocals to sound sweet and elevated. This is probably the most coloured part of the entire frequency range – but especially for female vocal lovers, it is a colouration I really like.
  • Lower treble has less emphasis overall and the only real peak is at 6-7 kHz and this is actually slightly less in amplitude than the upper mid-range. There is simply very good overall detail and clarity – but without too much etch or grain which some other IEMs overdo by trying to hard. Overall this area does not over-emphasis simply because the bass is so linear.
  • Upper treble – rolls off – but does not affect/detract from the overall signature.
Resolution / Detail / Clarity
  • Really excellent overall clarity, and this was especially so on older recordings (10cc's Art for Art's Sake) where some of the detail can be lost when bass bleed over shadows. The Fidue A83 simply goes about it's business – but without having to spotlight or overemphasis lower treble.
  • Cymbal hits have very good clarity and overall presence, and while they also have very good decay – there is a very slight hint of truncation which I don't get from the likes of the Dunu DK-3001 . This really is nit-picking though, and only noticeable if you are critically listening for it
  • Overall I feel as though I'm hearing everything in the recording – and this is even at my lower listening levels.
Sound-stage, Imaging
  • Directional queues are extremely good – very precise, and presentation of stage is definitely beyond the periphery of my head space with binaural tracks – so really good sense of width and depth. This (pleasantly) surprised me a little because I expected with the upper mid-bump for this to be less pronounced.
  • Spherically presented sound-stage – no issues with L/R dominance
  • There are very few IEMs which manage to totally immerse me in the audience with the applause section of “Dante's Prayer”. The Fidue A91 manages it easily, I'm there in the audience, and you can't get much better than that with an IEM. Easily as immersive as my U6, and I had to actually check to make sure that the Viper settings were disengaged on the X5iii. “Let it Rain” was my next track and it was again brilliant (very 3D like experience - the way the track was miked). There was the slightest hint of sibilance with Amanda's vocal – but again, its the way it is recorded – so not unexpected. What was great is that the sibilance was actually quite subdued, but the detail still shone through clearly.
  • Overall tonal balance and clarity – while retaining a very smooth sonic presentation
  • very good sense of stage and imaging
  • Detailed at low listening levels
  • Reference sound with slight colouration or forwardness in upper mid-range area. Transition between lower and upper mid-range is extremely good.
  • While I personally don't find it to be a weakness – some may find the bass to be a little linear. This could also depend on overall fit and anatomy.

The Fidue A91 Sirius doesn’t need amplification for overall volume – and because its impedance isn't spectacularly low, any source with an output impedance of less than 3 ohms should pair OK. All of my sources are pretty low OI and I had no issues with tonality changes. I don't tend to notice hiss (older ears) – so no real issues for me with the Sirius. The interesting thing with using the X5iii is that despite the balanced output being around 3 ohms (SE is lower), my daughter noticed no hiss – even at maximum volume (no music playing of course!)

Testing with the IMS HVA and FiiO A5Balanced with the SuperMini
With my iPhone 5S around 25-30% volume is more than enough with most tracks, and the FiiOs are generally at around 28-35/120. As I said, I have tried the A91 Sirius with the E17K, but also with my A5, and IMS Hybrid Valve but none of them seemed to be adding anything to my listening set-up other than some extra bulk. Although I do have to admit that I did quite enjoy the very slight tonality change with the iPhone + IMS valve amp, and using the A5's targeted bass boost was also an easy way to add some coloration if required.


In my opinion the A91 Sirius sounds beautiful with its default tuning, and I wouldn't personally feel much need (if any) for EQ. However I know that some may like more warmth and more bass impact, and this was easy to check with the X3ii and E17K combo. I used “Art for Art's Sake” again, and simply added +4 bass with the E17K. The resultant tonality was very good, and still did not detract from the clarity. I then took a much warmer recording (Dido's “Girl Who Got Away”, reduced the bass to neutral and added +4 treble. Again the change was immediate but really well presented. The A91 Sirius responds well to EQ, although again I am really happy with its default sonic signature.


Having the balanced cable option is nice, but I noticed no real change with the likes of the X7 + AM3 module once I had properly volume matched (using the Fidue A91 cable adaptor for fast switching). Personally I wouldn't be able to tell the two apart in a blind test. For those with DAPs where the balanced sounds better (different circuitry), its nice to have the option though.


These comparisons were all done with the X5iii, (no EQ or DSP) – and volume matched using a calibrated SPL meter and fixed 1kHz test tone first. Choosing the comparisons, I wanted to firstly compare against the former Fidue flagship (A83), and then with IEMs of similar ability and price range. This is always more subjective than objective, and I don't personally have access to a lot of IEMs around the $500+ mark. So I ended up comparing with the $300 Fidue A83, DUNU's new ~$500 DK-3001, Rhapsodio's older ~$800 RTi1 single dynamic, and 64Audio's ~$900 U6 and ~$1400 U10. Hopefully this gives enough insight to anyone interested in this IEM. Here are my very subjective personal thoughts:

Fidue A91 Sirius (~USD 900) vs Fidue A83 (~USD 300-340)
Fidue A91 Sirius and Fidue A83Frequency comparisons
Starting as usual with build quality – the Fidue A91 Sirius build quality is miles ahead of its older sibling both with materials used, and also the quality of finish. This is also apparent with the accessory range – especially with extra cable choices. Out of the box the smaller A83 might have the better overall fit, but once you get the right fit with the Sirius, I actually prefer it now to the A83 for comfort. And the big weakness with the original A83 (cable connection quality) is now completely fixed with the A91 Sirius. I would still say that the A83 might have slightly better overall isolation.

Overall sound quality firmly is in favour of the Sirius also (as you'd probably expect). The A91 has a much more balanced signature – and when Fidue describe it as “reference”, I can clearly both hear and see that this is the case. The A83 has more of that usual V-shape associated with a lot of hybrids, and the bass is more pronounced – but also boomier. The other big factor with the A83 is that the pronounced peaks also tended toward some grain in both upper mids and lower treble. I loved the clarity when I first reviewed them, but over time, and when comparing to more balanced signatures (DK-3001, Andromeda, and especially the Sirius), I've come to appreciate clarity without the peaks. The Sirius is a definite and definitive upgrade in virtually all areas, and IMO worth the upgrade and additional asking price.

Fidue A91 Sirius (~USD 900) vs Dunu DK-3001 (~USD 470-500)
Fidue A91 Sirius and Dunu DK-3001Frequency comparisons
Overall build quality is excellent on both, and neither skimp on materials. I would say that the overall finish on the Sirius is perhaps a notch up though. Accessories are on par – both have very good packages. The DK-3001 of course includes 2 cables (balanced and SE) where the Sirius accomplishes this with the adaptors. Dunu DK-3001 With fit and comfort – I have to give this to the Sirius. The smooth and rounded internal faces ultimately trump the DK-3001's slight internal ridges.

Sonically there are some similarities. Both are well balanced earphones in their own way – the DK-3001 having the more traditional shallow mid-bass hump, moderate dip in lower mid-range, and more extension through the lower and upper treble. Both have an upper mid-range emphasis. Where the DK-3001 shines is in its overall signature balance and extension throughout the frequency range. The Sirius accomplishes the same goals through different methods – a little less bass which allows the mid-range and lower treble to be well focussed without needing any further emphasis. I love both earphones for their signatures, and it is actually quite difficult for me to pick a preference on sonics alone. For my own personal preferences I've always appreciated a slightly cleaner and cooler sound - and for me personally the Sirius delivers this slightly better, but I could definitely see opinions being divided.

There is a big difference in overall cost between the two. If the cost wasn't a factor I'd lean towards the Sirius as a personal preference – but both are truly excellent sounding monitors, and if bang for your buck is a factor then the DK-3001 more than holds its own.

Fidue A91 Sirius (~USD 900) vs Rhapsodio RT1i (~USD 800)

Fidue A91 Sirius and Rhapsodio RT1iFrequency comparisons
Build quality and material is in favour of the Sirius – it is just a far better overall package. The build materials are solid on both, but its the fit and finish on the Sirius which is far more polished. Likewise accessories go to the Sirius. Fit and comfort are are about even. Both have removable high quality cables, but the Sirius comes with the balanced option(s).

Sonically there are a little more differences this time, with the RT1i being a
far more V shaped monitor with a definite upper-mid/lower treble peak centered at 5-6 kHz. Comparatively the RT1i delivers a fun sound which I still very much enjoy, but there is some heat which comes with some definite sizzle (personally I prefer it EQ'd down a little), and vocals have a little more distance. And it doesn't take a lot to correct this, but up against the more balanced and better finished Sirius, for the $100 difference it would be an easy decision for me. The Fidue Sirius is simply a better presented overall proposition.

Fidue A91 Sirius (~USD 900) vs 64 Audio U6 + G1 ADEL module (~USD 900)
Fidue A91 Sirius and 64 Audio U6Frequency comparisons
This seemed like a pretty fair comparison to me – similar price, similar driver count. For this comparison I chose to use the G1 module simply because it elevates the mid-range a little and should bring it marginally closer to the Sirius signature.

Build quality (materials) is firmly in the Sirius favour. Its going to last for quite some time with the use of the alloys and quality of the cable. You'll note with my U6 that I'm using the Linum Bax cable and thats because my 2nd 64Audio cable has broken at the 2 pin connector. I know 64Audio would have replaced it – but this time I wanted a longer lasting solution. Accessories remain with the Sirius – but the U6 has the ADEL modules and ability to tune. Fit and comfort is slightly in favour of the U6 – the ergonomic build is simply slightly more comfortable for me.

Once again we see a similar pattern – the Sirius has more linear bass and a flatter overall signature, while the U6 has the gentle V and more natural mid-bass hump. With the G1 module, both have a bump in the upper mids, but the U6 has more lower treble extension, and to be fair, needs this to counter the increased bass. Both are incredible monitors, and the main difference is the added warmth of the U6 – which again makes the Sirius a little cooler and cleaner comparatively. Ultimately this will come down to preference as both sound gorgeous. The interesting thing was (using E17K's tone controls as EQ) simply taking the U6's bass down by -4, and already it managed to drop some of the warmth out of the U6 – and get the two much closer. For me personally I still have a slight preference to my U6, but ultimately this comes down to the time I've spent with them and my own personal preference. If I only had the Sirius I would not at all be disappointed.

Fidue A91 Sirius (~USD 900) vs 64 Audio U10 + G1 ADEL module (~USD 1300)
Fidue A91 Sirius and 64 Audio U6Frequency comparisons
I wanted to pit the Sirius against the most expensive monitor I had access to – which happens to be the $1300 64 Audio U10. For this comparison I chose again to use the G1 module simply because it elevates the mid-range a little and should bring it marginally closer to the Sirius signature.

Build quality (materials) is again in the Sirius favour for the same reasons I outlined with the U6. The Sirius also takes the win for overall finish, quality, and accessories. The U10 wins on comfort, and also it has the benefits of tunability with the ADEL modules, and also has other benefits with the modules (they really do help with lowering my tinnitus issues).

Like the U6, we see a similar pattern – the Sirius has more linear bass and a flatter overall bass signature, while the U10 has the more natural mid-bass hump. With the G1 module, both have a bump in the upper mids, but the U10 has more lower and upper treble extension. Again the main difference is the added warmth of the U10 – which again makes the Sirius a little cooler and cleaner comparatively. I again tried dropping the bass response on the U10 down with the E17Ks tone controls and I was genuinely surprised at how close the two monitors perform. The Sirius still sounds a touch cooler and cleaner, but at -6 bass on the tone controls there is not very much difference between the two (and if anything I really like this new tonality on the U10).

So this goes to show that the Sirius is indeed flagship material, and definitely belongs in the same class with the newer $1K family of monitors becoming more prevalent. Which did I prefer? Well its really too close for me to call – and depends on the value you put on the ADEL system. For me personally its worth it (the price difference) but without having access to the U6 or U10, I could quite easily settle with the Sirius. It genuinely is that good.


Despite having these for more than 6 months, its surprising when you sit down for a formal review that you still discover new overall strengths in monitors you thought you knew.

The Fidue A91 Sirius is every bit the TOTL reference IEM which Fidue intended it to be, and I've come to appreciate its strengths even more over the last couple of weeks of critical listening.

Starting with build, design and quality of materials used – Fidue has really lifted the bar from their previous A83. Design and finish is up there with the best, and their new locking MMCX connectors are a great solution to some of the issues formerly with the A83. The modular cable system is also somewhat of a novel approach to managing consumers desires for different balanced and SE connectors – and actually works pretty well.

Sonically the Sirius is extremely well balanced with a largely linear frequency response coloured a little with a bump in the upper mid-range (which personally I really like). The result is a very clean and clear tonality, albeit with a slightly cooler or leaner overall lean. And while bass is linear, it is still beautifully presented and definitely present when called upon.

The RRP at around the USD 900 mark means that this is a reasonably large investment in an IEM but if you appreciate this sort of tonality I can honestly not think of a lot which will deliver this sort of total package. Despite the price point, I would still recommend them wholeheartedly – they just sound too good not to. For my part, I'd still love to see them get the ergonomics 100% right and a return to a lipped nozzle (and maybe slightly longer too) which would really complete an otherwise excellent monitor. For me a 4.5/5 or 90% review ranking.

I just want to close with thanking Michael for arranging the review sample, and apologise for taking so long with it.



500+ Head-Fier
Pros: Rich, beautifully dynamic and detailed, coherent and great sound stage, quality cable
Cons: That quality cable!! (heavvvvvy!)

[size=24.56999969482422px]Acknowledgment[/size][size=24.56999969482422px]   [/size]

Thanks @Tony-Hifi at for providing me the opportunity to submit an independent review of the Fidue Sirius A91 (I have no affiliation to either or Fidue). There's a good selection of Head-Fi reviews that articulate the performance of these far better than I, as a noob to 'quality' IEMs, could do. As such, I'll try and keep this relatively brief. 

About Me

I'm a recent convert to IEMs having previously shied away from them in favour of over ears. A hectic home life (wife, two & six year old daughters), means that a) I've had to become a bit more opportunistic in when & where I manage to grab listening time and b) my disposable income has serious competing priorities!! So suddenly the benefits of an IEM i.e. the practicality of something you can have to hand at all times, that isolates/doesn't leak & that for the same kind of money I'd typically look to spend on over ears, I can have something that's a 'do it all' option. It does mean that as an IEM noob, my experience to date is pretty limited, so please bear that in mind when considering my opinions. To date I've heard (& reviewed) the Etymotic ER4-XR & SR, I've bought & currently own the Noble Sage universal (which I love), and these Fidue are really only my third foray into upper mid/hi end IEMs.


Background, Stats & Packaging

In the interest of brevity; I'd point the reader toward the several other reviews to get a view of design considerations, spec & packaging.
When I collected these from the post office, I couldn't wait to get them home to try so gave them a sneaky peek and a quick listen in the car! Suffice to say, it became apparent upon unpacking and attaching the cable & tips, this is a premium/flagship product (as others have pointed out; it's surprising the product isn't front & centre of Fidue's, english, website; instead, it's a few clicks deep before you uncover it).  Upon first listening, using only my iPhone 6S Plus, these sounded a cut above what my limited experience (see section 'About Me'), of quality IEMs. More on that to come though....

Sources & Music

I listened to the Fidue mainly straight out of an AK70 and using the AK70 as a DAC with a MacBook Air. As mentioned above I also briefly listened to them direct from an iPhone 6S Plus. In all instances, they sounded great, were easily driven and no hiss was evident. In terms of music, my tastes are pretty eclectic & with the Fidue I listened to everything from alternative/indie guitar, electro, acoustic, classic rock and a bit of pop. There was no genre that the Fidue didn't help bring to life. I listened mainly to CD quality streams from Tidal along with a few hi res, ALAC, downloads from Qobuz I treated myself to over Christmas (Grimes, Alt-J, First Aid Kit & Donna Summer!). For completeness, I listed to several 256kbps downloads of the same tracks. They obviously flourish with the better quality downloads & highlight the differences between the lower & high bit rate tracks. It's not that they render the lower bit rate unlistenable but at the end of the day, why would you invest the sum of the money the Fidue demand and then skimp on what you play through them?

Fit & Comfort

I must admit I battled a bit with these from a comfort perspective. It sits very well in the ear & using a stock medium silicon tip getting a good seal was no problem at all. Whilst the side facing your inner ear is all organic, sculpted curves which I'd have like to have seen reflected in the other side of the unit but......
....the side facing outward has some square edges that, on occasion, did irritate my ears. Repeated use did seem to toughen my ears to it though! Another area for potential irritation I found was the edge of the cable connector where the cable feeds in.  
The thing though that exacerbated these comfort issues for me was the stock cable. It's equally a blessing and a curse in my experience. It no doubt adds to the product as a premium proposition; I dare say it provides sonic benefits as well as allowing modular connectors for balanced configurations as well as standard 3.5mm but it adds weight & bulk. At this price I don't think a separate 3.5mm cable would have been too much to ask. Adding the 3.5mm adaptor to an already weighty & bulky cable results in a fair bit of heft! Don't get me wrong, this thing is robust, could successfully be used as an offensive weapon and will no doubt outlast religion! Sat down using the Fidue, the cable is no issue. On the move though, gravity gets to work on that cable and those square edges start to become more acquainted with your ear. The one thing that would help here & which isn't included is a clip. As it is, I found myself having to support the weight of the cable by stuffing the upper part into the top of my jacket and/or bundling the adaptor connection into the same pocket as the AK70 - not ideal.    


My first impressions (in the car, when my impatience got the better of me), straight out of the iPhone, were , "wow"! These are a serious bit of kit. Out of the AK70, they're a whole world of better!! Compared to what I've experienced to date, these are like going from standard def to 4k TV picture. They're 'rich'; there's just more of everything! They pull stuff from low down and on the periphery of a mix & pull it clearly in to the track. This reads as if they might result in something that sounds crowded or congested but quite the opposite; they manage to pull all that detail in but as a cohesive whole, with great separation and across the widest and deepest stage I've encountered on my IEM 'journey' to date.  
As an ex bass player, I'm no means a basshead when it comes to headphones but I do tend to focus a lot on bass quality. The quantity & quality I find excellent; impactful but sufficiently tight punchy and that extends/decays well & naturally without bleeding into the mids. 
Mids are detailed, slightly (slightly), to the fore and provide a super accurate reproduction of vocals. They've even added sufficient clarity for me to decipher certain lyrics that I've previously been unsure of and never bothered to find out! Only on a couple of occasions did this result in vocals being emphasised slightly too much that the volume of them, in comparison to the rest of the track, made me wince a little.
Treble for me on these, is just right; non-fatiguing, accurate and without sounding overly sparkly/'tizzy'.  


Overall, these sound great to me; the best I've have had the pleasure to listen to yet. I've still to hear other TOTL models from other manufacturers but given some of those retail for double (or more), than the Fidue, I have a hard time believing that they're going to perform too much better than these. Which to me means, whilst not cheap, they're somewhat of a bargain relatively speaking.
Sonically, I have no hesitation in giving these five stars. Overall though I have to dock it one star as I find, ironically, the thing that is a major part of the premium package, i.e. the cable, detracts from its use as an IEM on the move. 
That said, I do believe though if you were to pick up a pair of these and an alternative after market cable for use on the go, you'd still have spent significantly less than many other TOTL units and have something that deserves to be held in the same high regard.
"My first impressions (in the car, when my impatience got the better of me)"
that was hilarious, i know that feeling


Headphoneus Supremus
Pros: Excellent Build, packaging presentation, thought gone into upping the overall Fidue name.
Cons: Low isolation, detected coherency issues in the mids and sound laboring at higher volumes.
Looking back on the year 2014 was the first time I heard the brand name Fidue mentioned, there was a lot of noise surrounding their first release 3-way hybrid, Fidue A83, and for good reason. It was ranked extremely highly by myself on a price to performance ratio reaching close to top tier earphones at a fraction of their price. With such forward motion It didn't take long for Fidue to stamp their name onto the vastly evolving portable audio market.
After their A83 Fidue released some middle/lower end models such as A73, they were all well received but fans dearly wanted a new flagship. Everyone was waiting on an A83 successor but Fidue themselves went rather quiet without a word of something new in the pipelines. That was until around 6-months ago while browsing facebook I saw some new images emerge on Fidue's page.
Their new hybrid is a 5-way design using x1 dynamic driver and x4 balanced armatures in each housing, we soon found out it was known as Sirius, or Fidue A91 and the promo images looked stunning. Today we'll be looking at the new flagship giving some thoughts, I will say there are some excellent aspects I perceive from Sirus but others I was left slightly questioning.
Fidue Sirius A91
Pricing from Penon Audio: $899 USD
  1. Model: FIDUE SIRIUS
  2. Color: Dark Grey
  3. Driving Units: 4 Balanced Armature driver & 1 dynamic driver
  4. Frequency Response: 4-45000 Hz
  5. Impedance: 20Ω
  6. Sensitivity: 113Db
  7. Input Power: 30mW
  8. Total Harmonic Distortion: <1%
  9. Plug: Protogenous 2.5mm balance stereo rhodium plating plug
  10. Cable Length: 1.3m 8cores silver plating OFC audiophile cable
  11. Converting Cable: 2.5 to 3.5mm quadruple balance converting plug; 2.5 to 3.5 mm universal stereo converting plug
  12. Applicable products: iphone, Samsung, HTC, Xiaomi, Meizu(all models), Ipad (Tablet&PC). It applies to 99% market electronic products
The new flagship is considered a top-end release in all areas visually. The unit comes in a wonderful black leatherette style box you keep and store Sirius inside (if you wish). The lid pops open held by two soft ribbons revealing the superbly built alloy earpieces and tips laid out before you. A word of mention, when I received this review sample the lid on my box was rather hard to open, almost like an airlock was holding it closed, I did try gently though it needed some force. When I strained the lid open one of the earpieces came flying out onto my bed. It was a little frightening for a first impression though possibly only this particular units storage box.
The original fluoro green outer packaging sleeve we know remains, It wouldn't be Fidue if we didn't have this artwork on each release outer boxing, its their brand stamp or trade mark logo and I do quite like the impression in puts across for a consumer.
Once you have the lid open you'll need to remove the first layer of the box to reach your goodies such as storage tin (a complete work of art in itself) and other accessories. Also flipping the first layer upside down you will find your balanced cable adapters which had me puzzled at first where they were located.
  1. User manual
  2. 3.5mm to 6.3mm cable adapter
  3. Airline Adapter
  4. Storage tin
  5. x2 balanced cable adapters
  6. x4 sets of silicon ear tips (XS/S/M/L)
  7. x1 Comply tips
  8. Warranty card
Once inside the storage tin you find your extra accessories in plastic bags, these include some comply tips, an airline adapter, 3.5mm to 6.3mm adapter for home amps and a strange looking metal object which resembles a guitar pick. Turns out this item is a tool for removing the cable from each earpiece and another even smaller piece for cleaning the vents on the earphone housings. There are instructions inside the included manual explaining how this is accomplished and I'll show a photo to explain. I do think the cable removal/cleaning tool is something you'll need to keep an eye on, its small and may vanish into the realms of your apartment or house if not careful. Personally, I have not used the tools however it seems Fidue recommend you should as a safety measure with the MMCX connections.
The large metal tin itself is sensational supporting a twist/off lid, the inside padded out with what appears a soft velvet material so the metal earpieces never rub or knock anywhere. Its also weighs quite a lot giving a feeling of quality when in the hand . On the lid you can see the Fidue logo engraved deeply displaying itself with a chrome like finished indentation . The tin again like the entire package gives a strong impression of high quality, I doubt however it could be placed in a pants pocket as its an oversize design which suits me fine for home storage, easy to use.
Build Quality:
Fidue truly have gone for something different than their previous earphones, they've really upped the anti on build quality for their new flagship. Gone are the plastic housings we've seen on past models, Sirius has full metal construction housing with excellent attention to detail. Probably the only thing which remains similar are the vent or fin detailing on each face-plate.
The entire earphone looks extremely mature or grown up over anything we've seen from this company before. When in person you really think you're looking at something built by Sony or the likes of a true craftsmanship. Sony H3 was probably some of the nicest build I'd seen, that was until I laid eyes on Sirius in person.
Photos simply don't do the build full justice, its more an art form than an earphone housing, with the precision of today's machining tools each earpiece is a true mirror image of the other. I also appreciate Fidue going for a more laid back colour scheme with Sirius, no more red/blue bright housings or loud colours stating their name. Fidue have upped the game substantially.
Each earpiece still retains a similar shape to their previous models however the size seems to be kept quite small considering the amount of drivers inside. The metallic grey coating over the earpieces works very well in combination with the cable locking mechanism and coloured collars. They support popular MMCX connections with a locking collar system implemented, its good seeing this new approach taken on-board and hopefully solves any connection issues.
Another thing to mention is the nozzles on Sirius have no raised lip or section to hold your tips on securely. Because of this you may find tips coming off inside your ear canal after removal occasionally. I really do wish this area had been treated differently, but it is what it is.
Cable Quality:
The excellence in craftsmanship doesn't halt at the cable. After some research I've found its an 8 braid silver plated cable terminated with 2.5mm balanced jack (the same configuration as Astell & Kern use for their balanced output). The cable is also sheathed with a material that makes it extremely stylish usually found from custom cable makers. Included with the accessories are x2 adapters we talked about earlier, these attach to the default 2.5mm balanced connection converting your Sirius for single end 3.5mm or balanced 3.5mm input jacks.
While I see the functionality having 2.5mm balanced jack as default I really don't know if the market is prepared for this as an everyday use. We're still much in the 3.5mm single end jack lifestyle and I do wonder if simply another balanced cable should have provided instead of these add-on accessories. The downside to needing the adapters with your iPod or older MP3 players is they must remain attached full-time, they add weight to the already sturdy cable and it seems odd overall from a consumer perspective to take this direction. I do see where Fidue we're heading although not sure if I agree with it totally. As for the cable quality its wonderfully built, when attached to the earpieces only adds to the pure attraction of Sirius, there's no two ways about it.
Areas like the MMCX male plug connection are well designed. The locking mechanism collar allows each plug to stay on tight and the housing can swivel (or be adjusted) before screwing them down tightly, afterward the housing will hold that position/angle you select.
Fit / Isolation:
Fit wise I had an easy time, the housings seat neatly inside the cavity outside my ear as the lower-end of the housing slips in behind almost locking the housing in-place. I'm able to jump up/down with them worn or even jog slowly. I will stress though this is just with my ears, some who experienced rough fit a with the earlier A83 model may also run into problems. Areas like the nozzle still have limited reach and you must really align the housing in the correct position to get a tight sealed fit depending on your tips used.
I was able to use the stock included large tips without much problem, considering the housing lock into my outer ear so well. Others on the forums have needed to try tip alternatives, many of them saying JVC Spiral Dot worked well. Others have wished there were more tips included.
Because the nozzle still provides limited reach you're going to have a downside in isolation, its an area Sirius cannot keep out lots of noise. I was able to hear traffic and ambient sounds quite easily depending on my situation and how loud my music was playing. I couldn't really recommend Sirius for someone who spends their day in busy cites or around hectic train platforms.
Sound Quality:
Sources used:
  1. Astell & Kern AK300
  2. iBasso DX90
  3. Shanling M3
  4. Tralucent Dac Amp One
Files used:
  1. All files 16/44 FLAC
To my ears the tonality of Sirius is slightly on the warmer side of neutral, particularly around the mid-range where it can come across as smooth or as another word sounding matured. The downside is those who admired direct vibrancy and energy from Fidue A83 may find themselves wondering exactly what Fidue tried to do. For myself I understand the smoother signature is to display a more evolved sound though those who seek drop of a hat clarity may be left wondering.
Areas like the upper mid-range still have some push at higher volumes but again its all put across with a slightly warm tilt to the mids and it can be confusing if you dislike any kind of veil or lack of vibrancy, I've found myself tempted to add some EQ to bring Sirius at a level I like.
The bass is slightly forward from neutral but only fractionally and it comes across to me having a slightly elevated mid-bass hump depending on the tips used, its not the kind of mid-bass that's overly intrusive or annoying but enough to hear its presence along with the accompanied sub-bass, it seems to show more presence at higher volume regions.
Areas like speed are decent and texture but its not the kind of bass detail or clarity I have heard from some cheaper IEMs in the past. T-Peos H-300 being a good example. I do hear decent extension but when compared to something like Tralucent Ref.1 the reach into lower territory from Sirius suffers in creating the deepest sub-bass notes and remaining tight. My overall thoughts on the bass are not negative nor anything extraordinary amazing either.
The meat of Sirius is its mid-range, where the life and soul of this earphone lies. Like mentioned the tonality comes across slightly thick, and warm which presents the mid-range with some maturity or a smoother perception. While the detail is quite decent it expresses itself more in the thickness of each note over throwing it directly at you with edge clarity, it uses weight to express detail. For me, when using higher volumes I find this note weight gets in the way of separation and imaging, it can make Sirius confused, unclean or overcrowded at times which I don't feel is a pleasing experience.
At lower volumes when the drivers aren't working hard Sirius maintains its true sound and its quite enjoyable particularly when idling late at night whilst laying in bed. Its just for me when an earphone begins costing roughly $1000 its ability to remain coherent without congestion or sound like its laboring is extremely important. Tralucent 1Plus2 being an excellent representative. At the end of the day its all relative to your standard or reference level so opinions will vary between each person depending on their preference and experience with other quality earphones.
Areas like timbre are quite good with piano and guitar if you're interested in a slightly unreal sound, if you close your eyes and imagine or visualize a live concert inside a hall Sirius can place that across depending on the genre or music you listen to. I need to stress though those looking for a direct A83 upgrade in the mid-range need to consider the changes made to this signature.
To these ears treble is slightly on the smoother side as well, Its not highly active or aggressive, It displays itself well throughout most tracks and has never become too forward or itching my nerves on sibilant or harsh. It sometimes takes a back-seat when the volume is loud as the mid-range comes forward and its thickness takes a front-seat, but again its not done in 100% clean manner.
Extension seems to suffer and the highs can sound a little rolled, if you're looking for a lot of shimmer, a treble head or needing your ears massaged by highs Sirius will not do that. Its more what I'd consider consumer friendly treble, a safe approach to not offend anyone.
The first day I tried Sirius was with a track I'd not listened to for sometime, Agnes Obel, - ”Aventine”, its the first album on my sd cards. It had me convinced Sirius used some form of magic as the depth on the left/ right channels had an uncanny level almost like a binaural recording. While Sirus does contribute to this later that day I tested with a few other earphones and it was indeed the mastering of that track, not Sirius all alone. So I can say the soundstage does have quite good width and depth on the each side channel, it can almost come across holographic but you must have the correct tips and recordings for it to express this character.
One area that suffers is again the lack of air around the presentation when lifting the volume, again the mids sound sluggish, thick and it can compress the soundstage. With another higher-tier earphone the soundstage should be able to 'explode' outwards with tracks when there's a climax, the amount of dynamics should hit clean and then leave as quickly. Sirius cannot do this and loses marks.
Separation / imaging:
Imaging as mentioned can hold great refinement at lower volumes, its able to place instruments around the stage on each channel and the stereo imaging is decent, but again if there's any congestion it loses balance and becomes loose, the thickness takes control. When an earphone is excelling at higher volumes the imaging and separation should hold tight posture, it should surround you and create a large wall of sound that can immerse you.
I am actually quite surprised Sirus cannot hold a higher level of separation, I understand its signature is on the thicker side but it really loses some marks from me, it simply doesn't become a stand out area I think 'wow, that's good'. Instead an area I need to listen for, it doesn't find me, I need to find it then become slightly underwhelmed what I hear.
I'm giving Sirus a total of 4 stars, most of them allocated towards the build quality, packaging and overall presentation of your purchase. Fidue have pushed the bar in terms of expressing quality from their latest product, the housings, cable, and appearance are all absolutely first class. It really is a beautiful looking earphone one people will ask you about in the street, pieces like the storage tin make it a complete package, a very exceptional one. I do think they should have provided a separate balanced cable over the adapters but its their choice.
When it comes to sound I cannot agree Sirius pushes any boundaries or excelling what could be done with its amount of drivers. These coherency issues I detect at moderately higher volumes and that laboring causing Sirius to lose separation tell me there's something going on with the tuning that wasn't finalized or could have been implemented more accurately. Now, one can argue Sirius isn't my signature and I'd agree its not though my reference point being the Tralucent brand Sirius is a way off even the aging 1Plus2 hybrid design which uses less drivers. For an earphone to excel it must be strong technically, then you begin to draw a sixth sense from music, you begin to extract emotion, goose bumps, all those fun things. Sirius barely has the technical aspect nailed consistently. 
I do hear its ability at lower volumes, its a decent sounding IEM, but decent for $899 is not enough. For almost $1000 I want amazing, I'm paying you so provide that sound. Receiving Sirius as a review sample I need to ask myself how my conscious had felt if I paid the full amount, would I be pleased with its sound performance? My answer is no, I would not be completely satisfied for the money and need to be honest. At the end of the day its not my cup of tea though others will always feel different and I hope they enjoy their purchase, genuinely.
Thanks to Michael from Fidue for sending the sample.
Pros: Well above average soundstage, great instrument separation, excellent details, full bodied, speedy, easy to drive, excellent build quality, beautiful
Cons: Harsh treble and artificial mids on some tracks, shallow insertion, potential vent blockages change sound, large shell won't fit all ears, price




Thanks @Tony-HiFi for loaning me the Fidue Sirius A91 for the purpose of providing an honest review.



Sirius is the brightest star in Earth’s night sky, so bright that under ideal conditions it can even be viewed in daylight. Sirius, an illuminated compass for dividing up the night sky to Polynesians and Ptolemaics. In early Catholicism, the position of Sirius in the firmament was used to guide the timing of nightly prayers. Will this new flagship release from Fidue scorch the inner universe of the ear leaving a glowing ember in the night sky of memory (from Ancient Greek Seirios, glowing or scorcher), or will it be the ‘dog star,’ a cause of cacophony and fevers in the waxing hot ‘dog days’ of summer?
The Sirius A91 is Fidue’s entry into the flagship headphone market. Fidue has been casting its light into ever more ambitious markets while also improving on the fit and finish of their lower end releases. Earlier this year I had the pleasure of participating in a tour of the Fidue A65, a beautiful, under $75 headphone released in 2015. The Sirius isn’t in the same constellation, nor should it be. Fidue’s offerings on the high end have long been moving into more complex hybrids IEMs. Last year they released the A73 (2 driver, 1 dynamic driver, 1 balanced armature); and in 2014 they released the A83 (triple hybrid, 1 dynamic driver, 2 balanced armature). I think they’ve been scaling up their capabilities for this release for a long while. The Sirius seeks to establish Fidue as the brightest star in the night sky, with five drivers (1 dynamic driver and 4 balanced armatures) striving to push the IEM to a distant zenith. Will it succeed? Will its bright light be white hot stellar light, or a more localised Martian glow?
For all my reviews, I include a section that describes what I like. If you’ve read it before, or aren’t interest in my particular set of biases, let the music play on and scroll your eyes to the next section.
Like most sensible people I started falling in love with music as a child. My first portable audio device was a Sony Walkman (the cassette kind) that I got when I was 10 years old (24 years ago).  I listened with the cheap Sony on ears that came with the Walkman until I bought a Koss CD boombox and started listening to UAF College Radio and 103.9 (alternative rock at the time) in Fairbanks, Alaska. I once listened to Louie, Louie for 3 days straight, and I’m not insane—did you know there is a Spanish gospel version of Louie, Louie?
Like political tastes and tastes in friends, my musical tastes evolved through association and then rebellion and experimentation. From the songs of my father (The Beatles, Rolling Stones, Bob Dylan, ZZ Top), to the songs of my peers (Dr. Dre, Green Day, Nirvana, Weezer), my tastes evolved, expanded and exploded into the polyglot love that is my current musical tapestry. Like a Hieronymous Bosch mural, my tastes can be weird and wonderful: dreamy Japanese garble pop, 8 bit chiptune landscapes percolated with meows, queer punk, Scandinavian black metal; or they can be more main-stream with minglings of Latin guitar, Miles Davis trumpet, and banks of strings and percussion in the Mariinsky Orchestra. Mostly my audio drink of choice is a rich stout pint of heady classic rock and indie/alternative from my musical infancy and identity formation (the 90s). Come as you are, indeed. Beyond the weird, the wonderful, the interesting and accepted, I’m a big fan of intelligent hip-hop artists like Macklemore, Metermaids, Kendrick Lamar, Sage Francis and Aesop Rock. I even dabble in some country from time to time, with First Aid Kit and the man in black making cameos in my canals.
My sonic preferences tend towards a balanced or neutral sound, though I’ll admit to liking a little boosted bass or treble from time to time. If I have to choose between warm and bright, I’ll choose bright almost every time. A few screechy high notes are preferable to me than a foggy unfocused bass guitar. As my tastes are eclectic, and a day of listening can involve frequent shifts in my sonic scenery, I don’t generally want headphones that try to paint my horizons in their own hues. I need headphones that get out of the way, or provide benign or beneficial modifications. I desire graceful lifts like an ice-dancing pairs’ carved arc, not heaving lifts like a man mountain deadlift.
My last hearing test with an audiologist was a long time ago and under strange circumstances. However, I have heard tones all the way down to 10hz and all the way up to 23Khz using headphones in my collection. Either my headphones tend to have a hole in frequency at 18kHz or my hearing does, because I never seem to hear it. I’m sensitive to peaky treble, and treble fatigue, even when I can’t hear what might be causing it. I do enjoy smooth extended treble. I like deep tight bass and impactful drums, and dislike upper mid-bass emphasis.  I like my vocals crisp, so stay away from Josh Tillman’s voice you nasty upper mid-bass hump.  I like air in the stage, not just cues to distance and height, but the feeling of air moving around and through instruments. Soundstage shouldn’t be just about hearing, I need to feel it. I listen at volume levels that others consider loud (78 to 82 dB), but I just set it to where the dynamics peak. I’m not here to shatter my eardrums. I like them just how they are.
I generally don’t believe in using EQ, not even for inexpensive headphones, especially in reviews. I won’t claim that I haven’t done it, but I generally try to avoid it.
I believe that burn-in can make a difference, but I also acknowledge that there isn’t any measurement that appears to give conclusive proof that burn-in exists. I trust my ears, fully acknowledging that my brain may fill in expected details, may colour my interpretation, or may be subject to its own settling period with a headphone. In my experience, burn-in effects are not as large as proponents of burn-in tend to advertise. I’ve also noted that using white/pink/brown noise, I almost never observe changes beyond 24 hours of burn in. When people tell you that you shouldn’t listen to your headphones until they have 200 hours on them, I think these people need to be ignored. No matter what, you should be listening to your headphones at different stages, right out of the box and at intervals. How can someone observe a difference without baseline observations and follow up observations to measure change trajectories? If you really want to be serious about controlling for effect, you need volume matching, source matching, and tip/pad matching.
I’m a firm believer that cables can make a difference, but I don’t think they always do. When I tried out Toxic Cables line, they were in a bunch of baggies at the Cambridge 2015 HeadFi meet without any labels tell me what I was listening to. The cheapest looking one was the one I liked the best. I was excited that I wouldn’t have to spend much to improve my sound. It turned out that the cheapest looking one was the Silver/Gold top of the line cable. I’ve heard the difference that USB cables can make, from upgrading from the crappy cable that came with my Geek Out 1000 to a Supra USB, and then again when upgrading to the LH Labs Lightspeed 2G with the iUSB3.0. When I picked up a cheap shielded power lead from Mains Cables R Us to replace my standard kettle lead on my integrated amplifier, I heard more crunchy and clearer treble. I switched the leads with my wife blinded and she heard the same difference. I didn’t tell her what I heard and let her describe it herself. But cables don’t always make a difference. When I switched from my standard HD650 cable to a custom balanced cable (Custom Cans UK, very affordable), the sound stayed exactly the same when hooked up via a top tier (custom made by @dill3000 silver/gold Neotech wire) 4-pin XLR to 6.3mm converter. Balanced mode made a difference in clarity and blackness of background—this indicates that the amp was the deciding influence, not the cable. Your mileage may vary and you may not hear a difference, but I have.


Vital Statistics (specs from manufacturers and distributors)

Not all stories are written in constellations, poured over by astrologers and other augurs of signs and portents, most stories now are written on the internet. Banal stories on youtube, twitter rants, and journalistic endeavours from talented writers spinning stories of bat and ball, pads and impact on my favourite Seattle sports sites. Producers of high end audio gear tell their stories on the internet, too. I feel compelled to give voice to these stories of industry told through statistics, sensitivity, driver counts, frequency response and small or large doses of marketing stimulants and bromides.
Fidue’s website is difficult to navigate, and insufficiently populated with data on the Sirius A91 for my liking—it’s your flagship, put it on the front page and have good links to information on it—so I have relied on HiFi Headphones for this section of our tale.
Equipped with a 5-way hybrid driver combination, including four custom-made premium armature drivers plus one exclusive dynamic driver, the FIDUE SIRIUS A91 IEM offers reference-class sound with outstandingly accurate and detailed imaging.
As the Flagship model of the FIDUE range, the SIRIUS A91 uses four custom made balanced armature drivers along with a custom built super bass dynamic driver unit. This unique design results in a superbly detailed, accurate and neutral repodruction with clear and enhanced trebles while the custom made dynamic driver adds great warmth in the low frequency spectrum without any distortion. The detachable cable is an 8 core, silver plated, ultra-low internal resistance audiophile balanced cable, with FIDUE's 4th generation MMCX locking design.
With beautifully sculpted full metal shells with a striking, finned design. A selection of single, dual-flanged silicone and foam eartips provide a snug fit and excellent noise isolation for unparalleled comfort even in long listening sessions.

Single Exclusive Super Bass 10mm Dynamic Driver / Four Custom-Made Balanced Armature Drivers
Frequency response
4Hz - 45kHz
113 dB
Rated power
30 mW
Main cable
1.3m Braided 8 core silver-plated ultra-low internal resistance audiophile balanced cable (2.5mm Rhodium plated jack plug) with a 4th generation locking MMCX connector
Adaptor cables
2.5mm TRRS female to 3.5mm TRRS male (balanced) Rhodium plated plug
2.5mm TRRS female (balanced) to 3.5mm TRS male (unbalanced) Rhodium plated plug

Form & Function

Packaging and accessories

The Fidue Sirius A91 comes in a small square box. The box is wrapped tightly in a paper branding band that I struggled to get off without ripping. I had to be slow and patient, characteristics I’m gaining much more experience with from baby mealtimes. After the wrapper is safely removed and set aside, the box is a leather box with foam inserts to aid in safe transport of all the sexy audio innards. The top of the package has really nice foam tray for holding the shells, with a classy blue ribbon used for pulling out the adaptors on the underside. The IEM tip storage is another story, it’s a cheap blown plastic number that the IEM tips don’t want to go back on once you’ve taken them off—a bit of a pain for a review unit that you want to return in pristine condition. Below the tray the aluminum case ornamented in laser etched edges and lettering, with a dimpled waist can be found. Pulling up on the lid reveals the headphone cable. Along with all the other gubbins you’ll find your warranty card, an airline adaptor, a 3.5mm to 6.3mm adaptor, and a guitar pick tool and some desiccant—do not eat—for keeping everything dry and bug free on the long journey from China. The guitar pick tool is used for releasing the MMCX connectors, trust me, you want to use the tool, and not to channel Jimi, but I bet you could play some Little Wing, if you like.
I was both really impressed with the accessories and a bit disappointed. I think that every headphone manufacturer should make their headphones balanced, and include adaptor cables. That Fidue has included adaptor cables for standard 3.5mm TRS and for 3.5mm TRRS (HiFiMan balanced) is impressive to me and is a big point in their favour. I wish I could just buy the cable, and adaptors like on the A83. Maybe that will be an option in the future. The selection of tips was limited, but I found the Fidue tips to be of very high quality. I tried the comply foams, but they made the sound too warm for me. My favourite tips with the Sirius were not the ones that came with the IEM.

Build quality

The headphones are very solid feeling with a nice curvature to the back of the IEM. I didn’t like the case, but it does have excellent build quality worthy of flagship status. The case looks pretty, but if I throw it in my bag I don’t think it will look pretty for very long. The case is good as a showcase for at home, but it contains no padding to protect the headphones and no compartments to store alternative tips or cleaning tools. Form isn’t enough for me, which is why this section is called form & function. Fidue’s intended function for the case is clearly to look prestigious—mission accomplished.

Fit & Function

The Sirius has large earpieces, so fit may be an issue for some people, but it was not for my medium sized ears. The earpieces have a shallow fit with a relatively short nozzle. Another thing to note is that the ports on these are inward facing, so if the port is blocked, you’ll effectively turn the bass up on these. The headphones are comfortable over the ear, and the cables help with this. I found that rotating the MMCX connector towards my head gave a nice tight fit of the cable above my ears.
At first blush, I was not a fan of the cloth cable. I managed to quickly tangle it, and it took me a while to figure out how to use it and not have it become a Rapunzel nest of fibre. Once I figured it out, I was happy.
Jewellers say that Rhodium is an excellent and beautiful conductor, but soft compared to gold, which means that Rhodium plating will wear down more quickly than gold plating. Edit: From Victor Halgaard Madsen, on HeadPie, gold is softer, with a hardness of 2.5 mohs compared to 6 mohs for rhodium. The jewellers might just be trying to get people to re-plate their rings frequently. The plugs scream quality, a no expense spared ambiance, and allude to the bright radiance of the IEM’s Sirius namesake. Edit: audio sites say that Rhodium is better wearing than gold, whilst jewellers say that Rhodium plating wears off a ring in 6-24 months. I know that my white gold wedding band (often rhodium) has the yellow gold shining through quite a bit. I don't know who to believe, but I'd say if you have had the experience of your gold jacks wearing out, giving Rhodium a try isn't a bad idea, but don't be surprised if your results aren't any better. Also, buy your Rhodium plated gear from reputable sources, as a layer of Rhodium plating that is too thin will come off in no time at all. Don't go hunting from random east-asia source number five on aliexpress.
The Fidue A91 Sirius​
The Testbed​

Audio quality

For my listening time I tried the Sirius on a few sources. I played the Sirius out of my Note 2 (I really should consider upgrading sometime soon) long enough to know that I only needed to turn the volume up to 50%. The Sirius is plenty sensitive. I played the Sirius out of the Questyle CMA600i and I played the Sirius out of the LH Labs Geek Out V2 (low gain) in both balanced mode and single ended. I compared the Sirius to my two favourite headphones in my collection: the 64 Audio X2 and the Echobox Finder X1. I tried to volume match comparison using volumes between 78 and 82 dB using white noise and my cheapo SPL meter. I tried using a coupler, but couldn’t get a matched insertion depth across the IEMs, so I pressed the headphones with tips on to approximately the same location and same depth on the foam ball on top of my SPL meter and measured. I had to do a bit of tuning by ear on the 64 Audio X2, as the sound wasn’t quite right (I think it is the ADEL technology).
The Sirius claims some serious frequency response, reaching a Cold War era nuclear weapons cache depth on bass and an ‘oh crap supersonic explosions’ level at the top (4Hz to 45kHz). Specs like that paint the picture of having even extension to unfathomable levels at both extremes, and I was pretty sure that I wasn’t going to hear any of that, so I ran some test tones from and Binkster Test CD. I could not hear anything at 10Hz, but could feel the driver moving. At 16kHz the sound started to roll off. I’m not sure if aspects of this insane proclaimed frequency response show up in the sound. One thing that proponents of HiRes will often say is that people hear timing differences to 192kHz (pretty arbitrary frequency to choose), so anything beyond audibility on frequency, may still show up as audible on timing signals, which is really what gives a soundstage its feel. On another make of IEMs that report having frequency response up to 45kHz, the oBravo ERIB and EAMT series, I found that the soundstage was the best of any in ear I’ve heard and comparable to many high end full-size headphones. The Sirius has a good soundstage, with good depth and width, but it isn’t anywhere near the oBravo level of stage.
As folks who have owned more than a couple sets of headphones know, tips can make a big difference on the sound of an IEM. I tested the Sirius with the stock tips, the included Comply foamies, and Spinfits. I used Paul Simon – The Werewolf and Daft Punk – Giorgio by Maroder to do my tip rolling. I found that the stock tips had a nice balanced sound. Comply added a little bass body and warmed the signature up a little more—too much for my liking, and as usual for me, Spinfit was in the Goldilocks Zone (keeping with the stellar theme, the link is to NASA). Spinfit tips tightened the bass a bit, giving it nice diction, whereas before the bass was a bit smoothed, with a little bit of missing detail. The Spinfit also lends a bit more starch to the treble’s collar—I like it crispy, Zankou chicken.

The Sirius has a rich tonality with a deep rich bass, warm rich mids, and clear treble—but with some sound surprises slicing in. It’s a sound signature dripping with a Julia Child size dollop of butter, but every once in a while the matron of French cooking grabs the knife.
With the Sirius I sometimes heard a bit of harshness in vocals. With Keith Greeninger – The Harder That We Love the vocals were pushed forward more, introducing some harshness and making Keith sound shouty at times. On Smoke & Mirrors Percussion Ensemble – Udakrep Akubrad, I had some harshness in the treble and some percussion instruments that sounded unpleasant. I’m a big fan of percussion music, so having glockenspiel sound harsh isn’t good.
Listening to Bright Eyes through the Sirius was like listening to his albums completely anew. If the Brakeman Turns My Way had excellent clarity, instrument separation, and soundstage without feeling like any frequencies were given too much weight. Bass had great texture. Hot Knives threw down well defined characterful guitar strums. On Lime Tree, echoes in the soundstage haunted while violins emoted with bow and strings suspended in a deep and wide stage. The sound of the Sirius on Bright Eyes was organic and emotionally moving.
Djenting through Animals as Leaders – Kascade I was impressed with the speed and articulation of the Sirius. On 2Pac – God Bless the Dead, stage depth and instrument separation peel back delicious layers of rappers. The Sirius really showcases the rapper multiplicity and depth. I’m nodding my head along in my beat up office chair, wishing I had hydraulics on my work desk.
Todays playlist included the following:
  1. Bright Eyes – If the Brakeman Turns My Way, Hot Knives, Make a Plan to Love Me, Lime Tree
  2. Animals as Leaders – Kascade (Tidal HiFi)
  3. Pink Floyd – Wish You Were Here (DSD64 SACD Rip)
  4. Smoke & Mirrors Percussion Ensemble – Udakrep Akubrad, Juego de Relojes (DSD256)
  5. Roger Waters – Late Home Tonight, Part 1
  6. Daft Punk – Giorgio by Maroder (24/88)
  7. Paul Simon – The Werewolf (Tidal HiFi)
  8. Keith Greeninger – Harder That We Love (DSD128)
  9. 2Pac – God Bless the Dead
  10. Michael Jackson – Billie Jean (24/96 USA Vinyl Rip, 18DR)


Echobox Finder X1(Comply)

The Echobox Finder X1 has a smooth natural sound, with good speed, as does the Sirius (Spinfit) on most tracks. Both have good detail retrieval, but given the v-shape sound of the X1, the mids are more satisfying on the Sirius. The soundstage is significantly bigger on the Sirius with more detail and better instrument separation. On Pink Floyd – Wish You Were Here, vocals were more delicate on the Sirius with a touch of sweetness. Vocals and guitar didn’t sound quite as natural on the Sirius. The Sirius had a bad time of it on Smoke & Mirrors Percussion Ensemble – Udakrep Akubrad, though, with some fogginess in the bass and some harshness in the treble.
On Roger Waters – Late Home Tonight, Part One, soundstage is the name of the game, and the Sirius kicks the Finder X1 around the block on this dimension. Again, I find the vocal and string tone a bit sweet, with some hints of harshness in the violins. The sound is really coherent on the Sirius. The Echobox Finder X1’s v-shape doesn’t do it any favours on the mids. Something I’m noticing the more I listen to v-shape signatures, is that they don’t hold up to volume matching. Mids will basically always sound recessed and a bit unnatural. I think v-shaped headphones are made for when you are wandering the street with ambient noise messing up your frequency response. A v-shaped headphone in that situation sounds more balanced. With the comply foams the isolation on the X1 is stellar.
On most tracks, the Sirius was significantly sonically superior, but it didn’t play well with everything I threw at it.

64 Audio X2 (Spinfit)

On 2Pac – God Bless the Dead, the Sirius has a thick, present bassline with excellent kick. The multiple levels of rappers are suspended beautifully, but the X2 just about matches it. The X2 has a touch less resolution on the layered rappers and slightly less depth on the soundstage. I felt like it matched the Sirius on width and height for this track. Something I noted on this track, the Sirius sounded thin and mechanical when the volume was turned down, so I’m not sure that the Sirius will play well with quiet listeners.
On Michael Jackson – Billie Jean, it is apparent that the mids on the 64 Audio X2 are more forward, giving a nice presence to Michael’s voice. The soundstage is great. Drum impact really rocks on these phones. Violins are perfect weapons of emotion rather than being pointy instruments of sonic doom. Switching to the Sirius, snares slam like M80 firecrackers, Michael is a bit further back in the stage and the stage has more width.



The Sirius is a stunning package with some special capabilities in soundstage and resolution that make it worthy of flagship status. However, this dog star for me had too many howling dogs in July and not enough beacons in the night. On some vocalists and instruments there was harshness. The bass could be temperamental and I’m not convinced that I didn’t have some times where my ear partially occluded ports and changed the signature slightly.
If you like a warm rich sound, the Sirius might be right up your alley. For those looking for a more neutral/bright signature, which is more my style, it probably isn’t the flagship for you. It looks, feels and sounds premium. It has an excellent soundstage and great clarity and detail while having a rich tonality in a very coherent presentation.
That said, it wasn’t really my flavour. The rich sound was a bit too rich for my blood, and compared to the Echobox Finder X1 and 64 Audio X2, I found the sound quality to only be about a 5% improvement in ideal conditions, and on songs that faired poorly with the Sirius, less than that. I understand that when we get into flagship territory, diminishing returns have already ravaged your wallet, flipped it over and ravished it again, but this year, there are other headphones I would put on my buy list at lower prices than this one for my leaner sound preferences.


twister6 Reviews
Headphoneus Supremus
Pros: smooth detailed signature, harmonic coherency of 5 drivers, spacious sound, quality 8-core modular removable cable, beautiful design, accessories.
Cons: cable weight with adapters, price (in contrast to previous Fidue flagship), isolation, not for those with small ears.

The product was provided to me free of charge for the review purpose in exchange for my honest opinion.  The review was originally posted on my blog, and now I would like to share it with all my readers on head-fi.
Manufacturer website: Fidue.  Available from Penon and HiFiHeadphones.
* click on images to expand.

I have been following Fidue and testing/reviewing their earphones for a few years now, and saw them grow and expand with a diversified portfolio of budget single driver releases, dual dynamic and 2-way hybrids, and 3-way hybrid flagship which I still hold in high regard.  The curiosity of where Fidue would be heading next always crossed mind.  Can a manufacturer top their current flagship performance and take it to the next level?  We all have a wishful thinking without realizing how much risk is involved to push the design envelope further, to try to come up with something new and exciting, to make it stand out from the crowd.  As it turned out, Fidue wasn’t resting on their laurels, and instead they were working hard on their next big release.
They left no stone unturned and went all the way with a new flagship release, aiming high and naming their new model “Sirius” which refers to a star system with the brightest star in the night sky.  Call it a Star, call it a Rock Star, call it by its official A91 model number, but either way there is no denial this 5-way hybrid made a noticeable leap over their previous 3-way flagship design.  This was not just another incremental release to keep up with a race by adding more drivers.  It was definitely a risk because Fidue team spared no expenses which ended up raising the price.  I’m sure many Fidue fans were not expecting such price gap between A83 and A91, and I also think many don’t realize that it’s not just 2 additional drivers but the entirely new design.  So let me go into more details after spending the last month with Sirius, to share with you what I found and if it's justifiable to go from A83 to A91 (Sirius).
Packaging of Sirius is the first indicator of how far Fidue has come to distinguish their product as a true flagship.  You are still going to find a black and green outer sleeve, traditional with every Fidue product, and still can expect a detailed description and design highlights on the front and a complete spec list on the back.  Removing the outer sleeve reveals a faux leather storage box, and that’s where all the “traditional” unboxing comparison stops.  Right away you get a sense of a premium product, and lifting the cover reinforces that. 
Like a jewelry box where the top cover is secured by side ribbons so it doesn’t flip all the way open, once the cover is up you’ll find two Sirius earpieces fitted inside of a precise cutout in the foam insert with a textured surface matching the box exterior.  Below it, there is an area with silicone eartips resting on top of little stand-offs.  Removing the top foam layer reveals a round cavity cutout inside of the next deep foam layer with a beautiful all metal storage container and the rest of the accessories inside.
I noticed that a number of manufacturers raised the bar of their product unboxing experience, so I can’t say that Sirius unboxing was the most rewarding one I have ever seen, but I can definitely say it’s up there at the top and definitely many steps above the unboxing experience with other Fidue products I reviewed in the past, including their previous A83 flagship.
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While keeping up with premium packaging, you can be rest assured you also won’t be disappointed with accessories.  I already mentioned about eartips, 4 sets of silicone single flange pairs in XS/S/M/L sizes, and also a medium size pair of genuine Comply tips.  Personally, I would have loved to see more eartips included with this flagship pair of IEMs, especially since a number of people might benefit from a longer core/stem tips if you find nozzle fit to be on a shallow side.  Moving on, you have a typical “filler” set with airplane adapter and 1/4“ headphone adapter.  Although it's a filler for me since I don't have use for it, others might find it useful.
Now comes the good part!  I absolutely love the metal round storage container.  You can’t really call it a case since it’s not exactly pocket-able or portable, but its carved shape, rich finish, and etched company name on the cover look VERY premium.  Regardless if you are planning to store your Sirius gems in there or keep other accessories or IEMs/CIEMs inside, it makes a nice conversation piece on top of your desk.  At the same time, it would have been great to include an additional more practical storage case, maybe something like a soft drawstring pouch.
Next was a little surprise.  In a small plastic bag there was a little poker which I figured right away to be a cleaning tool for air-vents in a Sirius shell.  The surprise was a metal guitar pick with an etched Fidue logo.  I really did mistake it for a pick, thinking to myself that now I can feel like a rock star.  Not until I started to go through the pages of the included manual, which btw is very helpful, I learned this was a cable disassemble tool.  Due to a unique cable connection which is not as easy to separate by hand, this pick works like a charm when you need to disconnect the cable from the shell by inserting it into the gap between the attached connectors while slightly twisting it to separate the cable.  My only suggestion here would be to include a spare set of this tool, too keep one at home “locked” in a storage container, and another one on the go.
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The cable.
If you think I was done with accessories, hold on to your hat, here comes the cable!  A fully modular cable design with 2.5mm TRRS balanced headphone plug (A&K wiring adapted by many popular DAPs) and two additional adapters/converters with 3.5mm TRS single ended termination and 3.5mm TRRS balanced termination (HiFiMAN style balanced wiring).  With an exception of PONO dual split connector, you are covered to take advantage of all the popular DAP headphone outputs.  This means that you no longer need to invest extra money into replacement cable to go balanced.  Also a small detail but I like how the cable adapter interconnects were neatly hidden inside of cutouts underneath of the top foam packaging layer, including a ribbon you pull on to remove these out.
The advantage of this cable is not just its modular design, but also a high quality material with 8-core (8 separate insulated braids) silver-plated cable inside of a fine braided cloth sheath jacket covering the cord.  The housing of the connectors, both cable and adapters, is all metal with an easy to grip shape and a premium look with clear labeling, including a rubbery strain relief.  The plug itself features a premium Rhodium plated alloy which has one of the highest oxidation resistance properties, unaffected by air and water up to 600degC. 
The biggest surprise turned out to be the mmcx connector plug.  Anybody familiar with A83 will know that Fidue tried to come up with something different in there by using a locking tab to prevent cable from rotating around the connector.  Here they took it to another level, referring to it as 4th generation lock up design.  First of all, the connector housing is a 90deg custom mold which naturally guides the pliable cable behind your ears, eliminating the need for a memory wire.  The engagement of the connector is snappy and secure, to the point where you actually need to use disassemble tool.  And on top of that, you have a color coded (red - right, blue - left) locking ring which screws on top of the joint to secure the connection.  You don't even have to tighten the ring all the way, leaving a little bit of room to adjust the cable connector angle relative to the shell for a more comfortable fit.
Do I think this cable brings up the best in sonic performance of Sirius?  I will talk about it in the next section of the review, but can acknowledge that none of the replacements I tried showed a nigh’n’day difference in comparison.  As an overall comment, this modular design is great and very flexible, but it does add to the weight and makes cable bulkier.  The locking ring is cool but also overkill since mmcx connector joint is already secure, but at the same time some might prefer to be able to lock the cable rotation, especially due to 90deg connector housing.  Disassemble tool is an accessory piece you might want to keep nearby, but at the same time how often do you need to disconnect the cable on the go?  Also, I'm not a big fan of cloth sheath cable jacket, but it does a fantastic job in keeping microphonics away.  In general, if you are not satisfied or have some issues down the road, you can always replace it with another mmcx cable.
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Cable adapters.
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Replacement cables.
I know that not everybody believes or hears the effect of the replacement cable, and I respect that.  This section is not my way of trying to change anybody’s mind, but rather to share with you what I hear/feel which is obviously a subjective opinion.
Sirius (SPC) vs A83 SPC – I found sound to be nearly identical, maybe with a stock cable being a touch brighter, but it was hardly noticeable.  Obviously, I couldn’t test the original A83 cable due to a locking tab, but instead used another mmcx cable (exactly the same wires as in A83) which Fidue sells as a separate replacement accessory.
Sirius (SPC) vs Pure copper (Pristine CX1 cable) - a similar performance, though I was able to hear with a pure copper a slight improvement in sub-bass rumble, making it deeper and more textured.  Also, it adds a little bit of airiness to the sound, and makes treble a little crispier.
Sirius (SPC) vs Super BaX - has an interesting effect on low end performance, making bass tighter and more articulate, even a touch faster (tested many times, hopefully my mind is not playing tricks on me).  Mids get a little more clarity and transparency, like a shade of veil was lifted off.
None of these changes introduced a night'n'day difference since Fidue already invested into a very capable 8-core SPC cable.  I don't have any plans to switch to another cable since I'm happy with a performance of a stock one, but if I did - I would probably be going to Super BaX cable.  Also, Super BaX will be a good choice if you want something more lightweight with thinner wires.
I was always a big fan of the original A83 design with a faceplate that reminded me of open wings.  Just like I was happy to see Fidue scaling down exterior shell design of 3way A83 to 2way A73, I was also pleased to see them scaling it up to 5way A91 (Sirius).  Except this time we are looking at all metal shell with a rounded inner part facing your ear and a familiar layered "wings" stamped out on the faceplate with a company name across it.  To scale it up also means that the size of the shell becomes bigger to accommodate more drivers, filling up both Concha Cymba and Concha Cavum areas of my ears.  I didn't feel any discomfort thanks to a smooth rounded edge of the inner shell, and it worked quite well with my average medium size ears.  But I do have concerns where those with small ears might have a bit of a problem with this new universal shell.  For sure, if you had issues with A83 fit, Sirius might not be for you.
The faceplate design of the outer shell does have a few sharp edges, but they never come in a contact with my ears, so I was OK with it.  Inner side of the shell has 2 separate vents where I believe a smaller pinhole one is located right in the area across from the dynamic driver, and two other longer vents are there to assist with soundstage expansion and low end control.  I was worried at first about the location of these vents facing in, thus getting blocked, but I didn’t experience any sound variation as I had Sirius in my ears and moved around.  I did settle on another eartip pair with a longer stem/core, and that created a bit of an extra space, preventing vents from being blocked.  Keep it mind, with Sirius you will need to consider a proper eartip selection not just for an improved seal and fit comfort, but also to prevent shells from being jammed right into your Concha area.
From eartips selection to a nozzle, I actually found it a bit on a short side.  Also, the tip of the nozzle was smooth without any lip, something I wish Fidue would have implemented to make sure eartips won't slide off easily.  Through the metal mesh (earwax guard) of the nozzle tip you can clearly see 3 individual bores, assuming one for the low end (dynamic driver) and other two split between mids and treble covered by BA drivers.  Last, but not least, you can also find a clearly printed L and R marking inside of the shell.  Even so shell design is asymmetrical and easy to identify left/right sides with a color locking ring, I was still pleased that everything was clearly labeled to eliminate the confusion when replacing stock or after-market cables.
Overall, I didn’t find any show stoppers with a design or a fit, but do want to bring up a few things as a feedback to potential buyers as well as Fidue.  The most important point, there are plenty of universal fit IEMs that have a generic and uninspiring design.  Here, Fidue created quite an eye candy with an original shape that will definitely get you noticed.  I know it’s probably shallow to talk about the appearance, but many people go for CIEM not only because of a custom fit but also to personalize the look of your monitors.  Here, with a right selection of eartips to ensure a proper seal and fit, wearing Sirius feels like I have a pair of CIEMs in my ears, and I got nothing but compliments from everyone.  Just don’t expect the high level of isolation with Sirius like you would get with CIEMs.  Due to shell venting, even facing inward, sound isolation wasn't its strongest point.
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The fit.
Sound Analysis.
After 100hrs of burn in, I hear Sirius as having a nicely balanced full body sound signature with a neutral smooth tonality.  The sound is detailed, resolving, non-fatigue, and with a very natural smooth timbre characteristics.  What I was really impressed with, unlike some other hybrid IEM/CIEM models where low end seems to be a bit disconnected from mids/treble, here you have a unison coherency with a smooth detailed sound across entire frequency range.
Low end has a deep sub-bass rumble with a smooth analog texture that adds a nice weight under the mid-bass snappy punch which has a decent speed for a dynamic driver.  Not quite as fast as BA driver performance, but still with a decent attack and average decay speed making bass sound natural and realistic.  The bass is not super tight or very articulate, but it has an excellent control for a dynamic driver without spilling into lower mids.
Lower mids have a good amount of body which adds to an overall sound characteristics, but at the same time it doesn't add too much to the thickness of the sound, still keeping it well balanced and neutral, though far from lean.  Upper mids are very detailed and resolving, never too bright or harsh.  They especially shine when it comes to vocals, both male and female, delivering a very natural, organic, clear tonality.
Treble has a nice extension, good definition, modest amount of airiness and sparkle - it's there but in a moderate amount and not over the top.  You definitely not going to miss the details of your crash cymbals, but the sparkle of the extension tail will be on a shorter leash.  The sound is absolutely non-fatigue, without a single hint of sibilance - intended for an extended enjoyable listening.
Soundstage is close to a holographic 3D level, expanding in all 3 dimensions.  With that, you can also expect a great imaging with a very convincing placement and positioning of instruments and vocals.  At the same time, layering and separation of instruments is good, but not outstanding which in my opinion is a result of moderate amount of airiness and the smooth neutral tonality.
Sirius vs Andromeda - soundstage expansion nearly the same in all directions, though I feel Sirius is a touch wider, while Andromeda is a touch deeper.  Andromeda has a little more transparency and slightly better layering and separation. The quantity and quality of sub-bass and mid-bass are nearly the same.  Sirius has a little more body in lower mids, making sound more balanced, while upper mids are nearly the same, very detailed, resolving, non-fatigue, though Sirius is just a little smoother in upper mids.  Both have an excellent treble extension, crisp, well defined, detailed, but Andromeda has a little more sparkle and airiness while Sirius is a little smoother at the top.  Also, Sirius has zero hissing, while Andromeda has some.
Sirius vs Pristine-R - Pristine has a bit of hissing; soundstage depth/height/width are similar. Sirius has deeper, meatier sub-bass, while Pristine has faster mid-bass.  Pristine lower mids are leaner and little thinner in comparison, while Sirius has more body, and upper mids in Pristine are brighter and a little more revealing; Sirius upper mids sound smoother and warmer in comparison.  Pristine treble is crispier and brighter, but otherwise have a similar extension and level of airiness.  While Sirius is more balanced with a more natural tonality, Pristine is more reference quality with a flatter sound and more revealing tonality.
Sirius vs ES60 - ES has a little bit of hissing; soundstage is nearly the same, maybe with Sirius being a touch wider, but it's very close.  Both have a similar sub-bass expansion in terms of quality, but Sirius definitely has more sub-bass weight, while ES has a little faster mid-bass punch with overall bass being tighter.  Sirius lower mids have a little more body, but not by a lot; upper mids in ES are a little brighter and more revealing but still equally natural, detailed, and smooth.  Both have a clear and detailed treble with a great definition, but ES extends further and has more airiness.  While Sirius is balanced neutral, ES is more reference neutral when compared.
Sirius vs K10UA - very similar soundstage expansions, with Sirius being a touch wider.  Similar sub-bass extension in terms of quality, but Sirius has a more textured sub-bass rumble, a little higher in quantity; mid-bass punch is the same.  Lower mids in Sirius have more body and warmer, while upper mids in K10UA are more revealing and brighter, and a little bit grainier in comparison.  K10UA treble is brighter, crispier, more extended, and with more airiness.
Sirius vs A83 - both have a similar height/depth while Sirius is more expanded in width.  A83 low end is more lifted, both sub-bass and mid-bass are higher in quantity, but not by a lot.  Lower mids in A83 are thinner, definitely not as much body as in Sirius, and upper mids are brighter, more revealing, and at the same time noticeably harsher in comparison (just in relative comparison considering Sirius upper mids are smooth and detailed).  A83 treble is brighter and crispier, with more airiness, but it also sounds a little harsher in comparison to Sirius.  There is definitely more coherency in Sirius driver tuning while A83 follows a more common 3-way hybrid tuning where you can distinguish low end performance of dynamic driver and upper mids/treble brighter tuning courtesy of BA drivers.
Next to A83.
Next to Andromeda, ES60, A83, Pristine-R, K10UA.
Source pair up.
In general, I found no hissing with most of the sources and a clear black background.  Treble was well defined, crisp, and smooth.  Majority of differences were in bass performance and soundstage expansion.
L5Pro - wide staging, rich warm organic tonality, full body sound, great sub-bass rumble and strong mid- bass punch.  Clear detailed mids, detail smooth extended treble.
X7 w/AM2 - wide staging, crisp brighter tonality, leaner sub-bass, punchy fast mid-bass a bit north of neutral, overall tight articulate bass, leaner lower mids, very detailed upper mids, crisp well defined treble.
L3 - SE: average staging, great sub-bass rumble, strong mid-bass impact, well balanced lower mids and clear detailed upper mids; snappy crisp treble.  BAL: a little wider soundstage, bass a little more balanced and tighter in comparison to SE (a touch less sub-bass, and more articulate mid-bass punch). Similar lower mids and clear detailed upper mids.  Treble is a touch crispier, but very subtle change. Overall SE/BAL in here are very similar, but I do hear a slight advantage of BAL where overall sound is a bit tighter and a touch more detailed.
LPG - wide soundstage, tight detailed sound, nice sub-bass rumble and tight punchy mid-bass, very detailed clear mids, upper mids quantity is more balanced in comparison to other daps, crisp bright treble.  Very resolving and transparent sound.
Opus#1 - SE: wide soundstage, excellent sub-bass rumble and tight mid-bass punch, overall an articulate bass performance.  Mids are clear and detailed, very resolving, well balanced (similar to LPG).  Crisp bright treble.  BAL: soundstage is a touch wider in comparison with SE, sound is very similar to SE performance but I do hear a little better layering/separation, slightly more airiness too.
DX80 - wide soundstage, very balanced sound, excellent pair up with a great sub-bass rumble, nice mid- bass punch, overall bass is not very aggressive but tight and articulate, clear detailed mids, bright crisp treble.
X5ii - soundstage width just average, very good tight bass with a balanced sub-bass (moderate rumble) and tight punchy mid-bass, clear detailed mids, clear bright crisp treble.  Also a great pair up.
N5 - SE: a little hissing, clear detailed sound, nice sub-bass rumble, tight mid-bass punch, articulate bass presentation; clear detailed mids, maybe even slightly mid-forward, bright crisp airy treble. BAL: wider soundstage, sound is more balanced in comparison to SE, otherwise very similar to SE.
Micro iDSD (ECO mode) - wide soundstage, amazing holographic expansion, very balanced transparent layered sound, excellent sub-bass rumble, fast punchy mid-bass, tight articulate bass, very detailed natural mids, bright crisp treble with plenty of airiness.  Probably the best pair up.
Opus#1 SE and BAL.
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It's not an easy task for a company to make a leap from their own established flagship to a new one at 3x the price.  In my opinion it was a risky move for Fidue because many people might not be comparing this new IEM to other TOTL brand names/models but rather will try to justify if Sirius is worth 3x the price of A83.  If you think about it, Fidue is not just adding 2 additional BA drivers, but rather replacing current config with all new four premium BA drivers and a new exclusive Dynamic driver.  With a recent flood of Chinese DIY hybrids featuring 5+ driver designs, many people don't realize those are using either no-name or cheap entry level Knowles drivers (thus a reason for a budget price) and have a poor QC.  Here you have premium drivers, all metal premium high quality shell, new improved mmcx connectors, 8 core SPC premium balanced modular cable with Rhodium plated plugs, nice accessories - all a big leap in the design backed by Fidue reputation and QC.
Furthermore, you are dealing with a more mature sound tuning in comparison to A83, where Sirius has a nicely balanced full body sound signature with a neutral smooth resolving tonality and a very impressive soundstage expansion.  If an improvement in overall build and design is not enough to convince you about added value, which also contributes to an additional cost, in my personal opinion the sound tuning of Sirius propelled it to the level where I feel it deserves to be compared to other TOTL IEMs/CIEMs, some at much higher price.  I believe Sirius crossed the threshold and reached TOTL level where you're no longer judging it as "good" or "bad", "worthy" or "not worthy", but rather looking at it as another flagship where it comes down to the sound tuning preference.  For sure, Fidue raised the bar with Sirius release and now ready to play with big boys!
Awesome review, very detailed, easy to read. These IEMs transpires quality with a big Q.
As you kindly underlines in your conclusion, the price could be justified by built quality, good QC and good aftersale. Something that is not usual for chinese competition (with a few exceptions like Cayin).
I always admire how people spend 500$ for a so called "high-end" unkown chinese IEMs, it's like playing a lottery, you can get an epic pair of IEMs but you can slo get a sloppy product, just due to inexistant QC...
Outstanding review Twister,and as usual,excellent quality pics-many Thanks
Hi. Would you consider A91 as reference-sounding? While Fidue advertises A91 as a reference-tuned monitor, it seems that several reviews mentioned that mids, especially vocals, are quite colored. At this time around the price has gone down a lot in Japan but I have no chance to try. It would be great if I could here your opinions on whether it's reference-sounding as the quality of being reference-like is my priority.
Pros: Large soundstage for and in-ear monitor, Spectacular midrange and vocal presentation, Combination of musicality and balance, World class build quality
Cons: Tip selection could be better for the price, Not for those who want a consumer oriented sound signature, Design might not fit smaller/deeper ears
At the time this review was written, the Fidue A91 Sirius hybrid in-ear monitor was listed for sale on Hifiheadphones and Penon Audio's website. Here are links to their listings of the product:
I’m a Fidue fanboy. I’ll be the first to admit this.
My admiration of the company started with an opportunity to review the A83 hybrid in-ear monitor. To this day they are an incredible sounding earphone. The A83 was Fidue’s flagship for almost two years prior to the release of the Sirius. After enjoying the A83 for over a year, I also purchased the A73 and A65. The A73 immediately became a personal favorite. I reviewed both the A73 and A65 as well. All three earphones are great for their asking price and to this day are all still very relevant.
When I heard Fidue was releasing a new flagship named Sirius, I was immediately fascinated. I knew they were something I would want to experience. I contacted Fidue and expressed interest in covering them. I was fortunate enough to receive a sample. I have had the pleasure of listening to them for the last few weeks and am ready to share my experience with Fidue's new flagship in-ear monitor. I hope my review captures the essence of this incredible earphone, and gives you the information you need to know when considering them as your next high end earphone purchase.
I was given an opportunity to review the A91 Sirius in exchange for my unbiased opinion and review. I am in no way affiliated with Fidue. I would like to take this time to personally thank them for the opportunity.
My Background
I AM NOT a numbers and graphs audiophile or sound engineer. Personal audio enthusiast? Absolutely! Headphone junkie? Possibly…
There’s something about quality DAPs, DACs, Amplifiers and Earphones that intrigues me. I want to hear any earphone that looks promising, in hopes that I can share my impressions with  enthusiasts and help them find the audio product they’re looking for. My Head-Fi profile has a list of audio products ranked from favorite to least favorite. For me, this hobby is more about getting great price to performance ratio from a product, and having a variety of different gear to mix and match. With personal audio gear, we tend to pay a lot of money for minor upgrades. One thing I’ve learned over the last few years is that just because a headphone has a higher price tag, it doesn’t mean that it has superior build and sound quality.
I’m always looking for great audio at a great price. I’m after headphones and IEMs that give me the “WOW” factor. I can appreciate different builds and sound signatures as long as they are solidly built, with ergonomics and sound that is pleasing to my ears. It’s my pleasure to share my experiences with audio products and make recommendations based on gear I have owned and used.
The Sirius comes in premium box that is wrapped in a cardboard sleeve. The sleeve is black with green and white accents. The front of the box features the brand and product name, along with key features of the product in fine print.
The back of the box displays specifications in three different languages, and some artistic verbiage about where the Sirius name comes from. For those who don’t know, Sirius is the brightest star in our galaxy.
Removing the sleeve reveals the premium synthetic black leather coated box which flips open to show the earphone housings and silicone tip selection.
*Please click on the pictures for a larger image
The housing and tips are set in a removable foam and synthetic leather inlay. The underside of the foam inlay holds two adapters for the Sirius cable. They’re a 3.5 mm TRRS four pole balanced cable, and 3.5 mm TRS  three pole cable adapter for standard (unbalanced) music sources. Removing the top layer gives access to a quality assurance card, owner's manual and a premium metal canister which holds the Sirius cable which is terminated in a 2.5 mm TRRS four pole balanced jack. Also included in the canister is a quarter inch adapter, airline adapter, cleaning tool and MMCX removal tool.
Specifications and Accessories
Drivers: Single Exclusive Super Bass 10mm Dynamic Driver / Four Custom-Made Balanced Armature Drivers
Frequency Range: 4Hz - 45kHz
Impedance: 20Ω
Sensitivity: 113dB
Max Input Power: 30mW
Distortion: <1%
Plugs: 2.5mm/3.5mm Balanced and 3.5mm stereo, Rhodium plated
Main Cable: 1.3m
Conversion cables: 0.18m
1X Pair FIDUE SIRIUS A91 Reference Class 5-Way Hybrid In Ear Monitor
4X Silicone eartips (XS/S/M/L)
1X Cleaning tool / disassembling tool
1X Comply foam tips (M)
1X Flight adaptor
1X ¼ inch stereo jack adaptor
1X Luxury aluminium carrying case
Every component of the Sirius package is premium with a slight exception being the tips. The black silicone tips are relatively standard in terms of materials used. The single pair of medium T-500 comply foams is nice, but several sizes would have been more ideal. I would have liked to see a more premium and larger assortment of tips come with the Sirius. It would be a negative experience for someone to purchase these and come to find out that they can’t find a tip that creates a consistent seal. Fortunately for me, I have lots of aftermarket tips to try with these earphones.
The build quality and aesthetic of the Sirius housings are stunning. They’re a cleverly constructed gunmetal gray aluminum shell. It’s relatively lightweight for its size, and is larger than your average in-ear monitor. The Fidue inspired layering is formed on the outside of the housing, similar to designs with the A83 and A73. The Fidue brand logo is printed on the outside. The inside of the Sirius housing has a few driver venting holes and L/R channel markers.
Nozzles on the Sirius are slightly wider and and shorter than the average in-ear monitor. There is no lip on the nozzle. These factors will make tip rolling a bit more of a challenge than average, although not incredibly difficult. For the most part it's a matter of applying some extra effort to get the tip’s bore to stretch over the wider nozzle.
The cable connects via MMCX plugs and jacks. There is also machined threads outside of the connectors which allows two very clever screw on fittings to hold the cable’s MMCX connections securely in place (More on this in a bit).
Cable, Y-Split, Cable Jack, Strain Reliefs
A very premium kevlar coated eight core silver plated stock cable comes in the package. The cable has very little spring and virtually no memory. It’s a little bit on the thicker side for a in-ear monitor cable and is noticeably heavier than average. The stock jack terminates in a 2.5 mm TRRS balanced jack. Two adapters come with Sirius. One adapter is for normal 3.5 mm jacks, and another for 3.5 mm TRRS balanced connections. Application wise, there is no need to purchase an aftermarket cable for most portable sources. Whether you have a standard or balanced output, the Sirius has it covered thanks to its clever cable and adapters. Owners of Astell & Kern, Onkyo, Hifiman and other portables with balanced output will be able to maximize the sound output and quality without having to shell out cash beyond the Sirius asking price. Although it is added (and unwelcomed) bulk, it does its job and works well.
Strain reliefs are heavy duty rubber and are well done. I have no concerns about cable shortages. The Y-split and straight style cable jacks and adapters are jacketed in metal and are very rugged. There’s nothing about the cable that looks like it's going to break any time soon. If there’s one thing that I would question about the Sirius cable, it’s the kevlar/cloth material used to cover the cabling. Although it hasn’t happened yet, I assume months or years of daily use could eventually cause the cable jacketing to fray.
The MMCX connection on each channel is excellent. Over the last year MMCX has become more and more popular, and also more and more scrutinized by audio enthusiasts. Over time, MMCX adapters can loosen and cause intermittent or total signal loss as a result of strain and daily abuse loosening the connection. Fidue has addressed this by adding a locking mechanism. After snapping the MMCX jacks into the housing, a metal ring twists into place around the connection, securing it in place and making it  just as strong as a wired connection.
The Sirius is all about maximizing the listening experience rather than being a cell phone companion. There is no microphone or remote that comes in the package. However, you can purchase an aftermarket cable with this feature if need be. If I had to guess, Fidue will probably release a phone cable with their exclusive MMCX locking mechanism in the future.
Ergonomics, Fit and Microphonics, Isolation
Although larger than the average in-ear monitor, I was able to get a fantastic fit. The bulkier size of the housing helped to fill the concha of my ear, and provide a secure and comfortable fit. The shallower fit could be an issue for some but I had no problem with this. Tip rolling, and finding a longer bore tip will extend the nozzle and remedy things if this is an issue for you. I wasn’t able to get a good seal with the stock tips, and foam tips seemed to impact the soundstage and made the sound too smooth for my preference. I was able to get a good seal with large Spiral Dot tips. One thing to note, the Sirius doesn’t create a vacuum like seal in my ears similar to many other in-ear monitors. Because of this isolation is average at best.
Microphonics are basically non-existent thanks to their over-ear fit. If you do experience microphonics, a chin/neck slider will help snug the cable in place and prevent the cable from rubbing against surfaces above the Y-split. I usually look for a chin/neck slider in an earphone to secure the over-ear fit, but the weight of the Sirius cable creates enough of a tug that I didn’t necessarily need to use it for the most part. Gravity holds the cable securely over my ears.
When using the Sirius for long listening sessions, the cable would create a small amount of irritation from the kevlar jacketing rubbing against the tops of my ears. I was able to easily remedy this by using a pair of aftermarket ear guides. To be honest I’m splitting hairs here. I don’t use ear guides for the most part because the discomfort is so minimal and only happens when listening to the Sirius for hours while on the go.  
Sound Review
I did my demo with my usual gear. I used an LG-V10 for smartphone use, and either my Shanling H3 or iBasso DX80 DAP/Bushmaster D14 DAC/Amp for high fidelity portable use. For desktop use, I used my Toshiba Satellite Laptop in combination with a ifi micro iDSD playing at 32/192 kHz. I tested them with several other sources as well. I used Google Music in its highest download quality (320 KBPS), and also streamed FLAC via Tidal streaming service. I also used purchased and downloaded tracks in MP3, FLAC, WAV and DSD. I make sure that any gear I test has sufficient playtime before writing a review.
I used my usual same songs for testing gear:
“Limit to your love” by James Blake (bass speed, punch, response)
“Doin’ it Right” by Daft Punk (sub bass)
“Get lucky” by Daft Punk (bass to midrange transition resolution, male vocals)
“Madness” by Muse (soundstage, separation)
“Some nights” by Fun (soundstage and male vocals)
“The soundmaker” by Rodrigo y Gabriela (texture and imaging)
“Bassically” by Tei Shi (bass to midrange resolution, female vocals)
“Skinny Love” performed by Birdie (female vocals, acoustic playback)
“One” by Ed Sheeran (male vocals, acoustic playback)
“Outlands” from the Tron Legacy Soundtrack (symphonic presentation, imaging)
“Sultans of swing” by Dire Straits (detail, separation, balance)
“And Justic for All” by Metallica (driver distortion, treble response, rock playback)
“Ten thousand fists” by Disturbed (driver distortion, treble response, rock playback)
Note: Other tracks were used, but the listed songs were primarily used to assess and break down the gear’s response.
Source Selection
Sirius comes in at a comfortable twenty Ohms. One thing I really appreciated was how well they worked with just about any portable and low powered source I had. I consider this to be a decisive advantage over many of the very sensitive top of the line multi-armature and hybrid earphones which can cause noise floor issues depending on what source they are used with. The Sirius sounded good with my smartphone, DX-80, micro iDSD, and just about every other portable source I tried them with.
The unique tuning of the Sirius didn’t necessarily discriminate low bitrate music files or poor recordings. They are slightly forgiving and won’t make your MP3s sound bad. They will upscale well and are pushed to their full potential when using them with your best files and source with a balanced output.
Sound Signature
*This graph was provided directly from Fidue
The A83, A73 and A71 were all at least to some extent bass forward, so I was expecting the A91 Sirius to follow suit. This wasn’t the case. The A91 Sirius bass is adequate in terms of quantity and quality, but it isn’t the most forward frequency in the mix, nor is it the star of the show this time around. The tuning will work with all genres, but won’t render the same bass forward response that many consumer oriented earphones do. The Fidue team has taken a more mature and high end approach to the tuning of their new flagship. The Sirius sound is very balanced and leans slightly towards a midrange forward sound and overall smooth presentation. The key word is SOUNDSTAGE (which I will touch on later).
Sirius sounds like a top of the line full sized headphone to my ears. The Sirius makes vocals and midrange instruments the star of the show, regardless of whatever genre you use them with. Their perceptually and slightly forward midrange presence combined with a tremendous level of quality, detail and texture in this range makes these earphones both unique and exceptional. Add a tremendously detailed, extended and smooth treble response, Sirius has a sound signature that is incredibly engaging and easy on the ears. This is done without sacrificing detail or extension on either end of the sound spectrum.
Another great feature about the Sirius sound is that I can enjoy them at any volume without feeling like I’m losing any sound quality. The Sirius sounds just as good to me at lower volumes as it does when I crank it up.
In terms of forwardness, I’m not going to say the bass of Sirius is polite, but it is the next step up from it. Bass of the A91 is responsive without being incredibly punchy. Extension and tone are world class. Sirius has dynamics that purists will appreciate. Bassheads might be wishing for more boost with these, but those who want a more natural and realistic bass response will appreciate this tuning.
In terms of sub bass, they aren’t rolled off at all to my ears. The Sirius extends to the limit of my hearing and hits every note easily. The balance and transition from the lowest of bass notes to midbass is pretty flawless. Midbass is decent and in nice balance with surrounding frequencies. The A91 midbass is on the softer side in terms of its attack and decay. Even still, things like midbass bleed don’t even need to be mentioned with Sirius.
When reviewing an earphone for review, I figuratively try to split hairs and find anything others could perceive as flaws. If there’s one minor caveat about the Fidue bass is that I wish it was a tiny bit tighter and punchier. With the A91 there’s a little bit more rumble than punch. Other than that it’s excellent.
Summarized, the bass of the A91 isn’t the star of the show, but it isn’t necessarily lacking in any way either. It has weight to it, it's extended and very adequate, but it isn't the prettiest girl at the dance. We're about to meet her in the next criteria.
This is where I find the Sirius to be magical. The keywords are balanced and beautiful. As compared to many other pairs of earphones, the Sirius midrange is perceptually slightly more forward than average to my ears, but without any perceived spike or drop. Midrange sounds, especially vocals will pop and take center stage in a magical way. The midrange is just a touch on the warmer side of neutral, and doesn’t render ANY sounds unnaturally to my ears. The dynamics, timbre and detail are insane for an in-ear monitor.
Fidue’s midrange is rich and dynamic without being artificial. Male and female vocals are great, and harmony is fabulous. When reviewing, I usually look for complex music passages to cause the earphone to lose its level of resolution, but with the Sirius I look forward to hearing complex layering of sounds. The Sirius handles it like a boss, and plays with a world class level of separation.
If you are a fan of acoustic music and live recordings, these are something I strongly suggest you check out. You won’t hear midrange as alive and vibrant as this very often from an in-ear monitor. Like I said before, the Sirius will sound good with just about any genre, but play something that calls for spectacular midrange and you will hit a sweet spot with them.
At the time of writing this review, I can’t think of an in-ear monitor that does midrange much better. I’m being “SIRIUS” when I say that :) (Sorry, I had to use that at least once in this review). There’s nothing I could identify as a fault. Maybe someone coming from a much colder sounding midrange would find them to be a bit colored.
Treble is detailed, extended and smooth at the same time. A lot of times earphones trying to achieve a “balanced” or “natural” sound will have some funky level of extension that is hard on my ears at louder volumes. Fidue has taken that edge off of upper frequencies without losing the natural and balanced feel. I can hear sibilant sounds without them being harsh. Some people might desire a little more sparkle, buy I really enjoy how the higher frequencies are presented on the Sirius. These are a fatigue free listening experience thanks the the smooth and detailed treble response. It’s refreshing to hear an earphone that doesn’t have any perceptual roll off while avoiding harsh spikes.
Soundstage and Imaging
What I’m about to say might leave some scratching their heads. I own a lot of earphones, but the best earphones I’ve heard in terms of soundstage is a properly driven Havi B3 Pro1. Yes, it’s a fifty dollar earphone, but hearing is believing. If you own the Havi B3 Pro1 you probably know what I’m talking about. When driven with the proper source, The Havi soundstage is world class.
The Sirius and Havi have a somewhat similar soundstage in terms of width. Take the Havi and relax the treble just a bit (while keeping the extension). Now, give the the Havi considerably more soundstage depth. That is what the Sirius is. The A91 soundstage is massive to my ears, trumping most of my full size headphones.
Midrange takes the center of the stage, with supporting frequencies that have plenty of detail, balance and extension. I consider the A91 imaging to be elite.
Campfire Andromeda ($1000 USD on ALO Audio's website)
The Andromeda is the earphone most people have asked me to do a comparison with. They are number one on my list at the time of writing this review. Their five balanced armature and patented “resonator box” delivers incredible fidelity. They are one of the most complete sounding earphones I've heard.
Comparing the two, the Andromeda is the cleaner sounding of the two, while the Sirius takes a more musical approach. The Andromeda is slightly brighter, slightly more detailed and extended at upper frequencies. Bass on the Andromeda is slightly more forward and tighter. Midrange of the Sirius is warmer, making the Andromeda midrange seem colder in comparison. Sirius has a more engaging midrange, and sounds better at louder volumes. In terms of preferences, those who like musicality, soundstage and vocals will prefer the Sirius. Those who prefer detail and extension will prefer the Andromeda. I feel blessed to have heard both. They both deliver world class sound quality.
In terms of universal driveability, Sirius gets the edge. With more powerful portable sources I get a background hiss from the thirteen Ohm Andromeda. Even still, matching the Andromeda with the right source, the sound is pretty amazing.
Build quality and design goes to the Sirius. The MMCX cable and adapters is more solid and universally applicable than the Andromeda. The Sirius is a more comfortable and easy to wear earphone as well. I give a slight edge to the Andromeda for accessories. Their leather case is more pocket friendly and their tip selection is a bit better.
Unique Melody Miracle V2 Universal ($1000 USD on Musicteck’s website)
The Miracle is an incredibly balanced and transparent pair of earphones. I consider them to be a more extended multi driver upgrade from the ER4 in terms of neutrality. Unique Melody’s six driver earphone produces an incredibly linear sound to my ears.
Comparing the two, the Miracle V2 bass is tighter and punchier than the more musical dynamic driver bass of the A91. Midrange of the Sirius is more engaging, dynamic and all around more fun to listen to than the more technical approach of the Miracle V2. Fidue’s flagship has another dimension of musicality and energy to its midrange presentation. In terms of treble, the Miracle V2 has a more more forward and technically accurate treble response. Sibilance in recordings will sound more natural, but also slightly harsher (especially at louder volumes). If you like “true to the recording” type of sound the Miracle V2 will be the way to go. If you are going for all out musical enjoyment and fatigue free listening, go for the Sirius.
Build quality and design goes to the Sirius. The Miracle V2 cable is cheap in comparison. The metal housing of the Sirius are superior to the acrylic build of the V2. Advantage goes to the Miracle V2 for accessories. They offer a larger variety of high quality tips.
If I took the earphones I have that cost five hundred dollars or more and put them in the hands of someone who doesn’t follow this hobby the way most of us do, and asked them which earphone they think is the most expensive, I can almost guarantee that most people would guess that it’s the Fidue Sirius. The build quality is heavy duty and truly extraordinary.  
The tuning takes midrange and soundstage to a level that isn’t often achieved from what I’ve heard in in-ear monitors. This goes for products that cost much more as well. The Fidue A91 is meant for the person who wants to maximize sound quality through their best portable or low powered desktop rig. If you want to take your listening experience to another level, and experience the midrange and vocals of your album collection all over again, I strongly suggest you try the Sirius.
When rating this product (and factoring in price), I have to take into account all criterias and average them out. I give the Sirius four and a half to five stars for build and design, four and a half to five stars for sound (depending on your preferences), and four stars for accessories (minus one star for lack of tip selection). All in all I give the Sirius four and a half stars. They are definitely worthy of their flagship status, and a top contender for the best universal in-ear monitors the world of high end earphones has to offer.
Thanks for reading and happy listening!
Good review Vince - we differ on a few points, but can agree that they are a very good sounding set of in-ears.
Excellent Review. I can relate to this - I'm also using my V10 as source. Thanks and cheers
Great review! You describe it the same way I heard it during an audition yesterday. It's probably my current favourite totl iem right now in terms of tonality and spatial qualities. Also appreciate the comparison with the Andromeda. I'm sensitive to treble, so I found the Andros has a little too much sparkle for me at the top end. But undoubtedly excellent technically as well.


Headphoneus Supremus
Pros: balanced & even sound, resolution, excellent integration of the dynamic driver, extension, very even treble, three included valuable adapter cables
Cons: potential fit issues due to large & edgy shells plus short nozzles, cable's cloth coating might fray over time, adapters don't fit case when attached


Benny Tan, Fidue’s chief engineer, has got more than 20 years of experience in developing and producing premium headphones and has already designed several products for some famous brands in the past. That the team with the people around Benny Tan and Fidue does not consist of rookies in the audio industry becomes obvious when one starts listening to their products – having had the honour, opportunity and pleasure to review their hybrid dual-driver A73, dynamic single titanium-driver A65 and UPQ Q-music QE80 triple-driver (which is an OEM version of the A83 by Fidue for UPQ) in-ears, I can thoroughly say that each of them totally convinced me and that I really like respectively even love all of them and find them incredibly musical as well as fun to listen to (each in their own way) without neglecting core strengths like control and resolution.
Development does never stop and now the time has come for Fidue ( to release a new product that will be nothing less than a flagship that has been precisely developed and tuned within the past two years. Being a hybrid in-ear again, equipped with four Balanced Armature and one dynamic drivers, their pinnacle of recent development that is called “SIRIUS” (after the constellation) will be Fidue’s pride. While it does not come cheap at an international price of US$899, its price is however still set below what some other manufacturers are charging for their flagship products, giving the steadily continuing price increments that are happening in the audio scene in the past few and recent years.

And you can believe me: I have had very high expectations for the SIRIUS. In the course of this review, I will find out whether the SIRIUS delivered or not.

Before I go on, I want to take the time to give out a hearty thanks to Fidue and their Michael for this opportunity and for sending me a sample of the SIRIUS free of charge for the purpose of an honest, unbiased evaluation and review.

Technical Specifications:

Price: $899/¥5678
Drivers: 5 (4x BA, 1x dynamic)
Frequency Response: 4 – 45000 Hz
Impedance: 20 Ohms
Sensitivity: 113 dB
Maximum Input Power: 30 mW
Cable: 2.5 mm TRRS balanced (including 2 adapters: 3.5 mm TRRS balanced and 3.5 mm TRS single-ended)

About Hybrid In-Ears:

As you can read from the technical specifications and mentioned multiple times in the preamble, the Fidue SIRIUS is a little different from most In-Ears and doesn’t only use dynamic or Balanced Armature transducers, but combines both in one shell.

Most In-Ears use dynamic transducers for audio playback which have the advantage of covering the whole audible spectrum and achieving a strong bass emphasis without much effort. Valuable dynamic drivers are often said to have a more bodied and musical bass that has a more soft impact and decay and lacks of the analytical character that BA transducers are known for. On the downside, in contrast to headphones with other driver principles, dynamic transducers often have a lower resolution.

Higher-priced and professional IEMs mostly use Balanced Armature transducers, which usually have got a higher resolution than dynamic drivers, are faster, more precise and have got the better high-level stability, which is important for stage musicians that often require higher than average listening levels. On the downside, it is quite hard to cover the whole audible spectrum with just a single BA transducer and strongly emphasised bass is only possible with multiple or big drivers. Some people also find In-Ears with BA transducers to sound too analytical, clinical or cold (in several active years in a German audio community where I wrote multiple reviews, gave dozens of purchase advice and help, from time to time I heard people that got into BA earphones for the first time using these attributes for describing BA earphones, especially their lower frequencies).

Hybrid IEMs unite the positive aspects of both driver principles and use one dynamic transducer for lows reproduction and at least one BA driver for covering mids and highs, wherefore the often as “musical” described bass character remains and the BA transducers add resolution and precision to the mids and highs – and that’s what the Fidue SIRIUS does with its technology. It is addressed to those people who perceive the clinically-fast character of BA transducers as unnatural, but want to keep the mids’ and highs’ resolution, speed and precision while having the musicality of the dynamic driver.

Delivery Content:

What I expected was a nice unboxing experience along with beautiful, valuable content.

And that is just what I got.
In contrast to Fidue’s lower-tier models’ packages, the SIRIUS’ is more square-shaped and is a chest that is made of black pleather (truth to be told, I was quite unsure whether it was real leather or pleather, but one layer on the inside revealed that it had to be pleather) that is covered by a black paper sleeve with white text on a green background, following Fidue’s well-known package design. The text does not only give information about the technical specifications in three languages (English, Chinese and German) but also general information about the in-ears and tells the buyer why the name “SIRIUS” was chosen (it is a quite interesting read, so check it out).
Removing the sleeve (which is quite difficult because of how tight it fits, and getting it back on is not any easy either), one is greeted by a silver “Fidue” and “SIRIUS” logo on the chest’s lid. Once it is flipped open, we directly get to see the detached in-ear bodies as well as four sizes of silicone tips that are attached on a separate panel.
This layer that is pleather-plated, too, can be taken out. On its back, the two cable adapters (2.5 mm TRRS to 3.5 mm TRS as well as 2.5 mm TRRS to 3.5 mm TRRS) can be taken out with the help of a blue stripe.
Below this layer is a nice manual with pictures as well as instructions, as well as a warranty card.
Last but not least, one will find a beautiful carrying case that contains a pair of Comply Foam tips, the normal 2.5 mm Balanced cable, an airplane adaptor, a 6.3 to 3.5 mm adaptor as well as a strange looking metal plate along with a pin that turn out to be for detaching the MMCX cables and cleaning the in-ears.

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Looks, Feels, Build Quality:

What I expected was a beautiful pair of in-ears with flawless build quality and a sturdy appearance.

The in-ears are made of two pieces (all metal) and feature Fidue’s unique three-dimensional scale design that however looks a little different to the A73’s and A83’s, to separate them visually. It is nothing but beautiful and has got a Fidue logo on the faceplate, as well as a shiny silver edge around the scales.
Through the protective mesh in front of the nozzle, three sound bores for the five drivers that are aligned in a five-way acoustic design can be seen.

As you might have noticed, the in-ears’ cable connectors are threaded which is because a locking MMCX mechanism was used (nonetheless every normal aftermarket MMCX cable can be used with the SIRIUS and the SIRIUS’ cable can be used with in-ears that have normal MMCX sockets as well). The counterpart is on the cable and screws in tightly so the MMCX connectors won’t turn (the SIRIUS’ MMCX connector and locking mechanism is one of the very few I personally trust in). And what is really nice is that the threaded collars are coloured, so it is super easy to immediately tell the correct side.
The cable is quite thick and fabric-coated, which looks nice but will very likely fray over time and also soak sweat and body fluids – you already see that I am not a fan of fabric-coated cables in general despite their beautiful appearance and I also would have personally preferred a cable with twisted/braided litzes although the SIRIUS’ fabric appears sturdier than that used with some other headphones and quite surprisingly, the cable is very flexible.
Apart from directly at the MMCX connectors, strain relief is really good. The y-split says “A91”, which is the internal designation of the SIRIUS. And very conveniently, Fidue’s flagship in-ear’s cable has got a cable cinch (chin-slider), which is really nice to see being finally implemented.
The 2.5 mm connector has got a Fidue logo and very conveniently, both cable adapters have got a small description (e.g. “2.5mm TRRS to 3.5mm TRS”), which might come in handy.

You might be probably wondering why the plugs have got a silver shimmer instead of the commonly seen gold. This is because Fidue decided to use rhodium-plated connectors instead of your everyday gold ones (if that does not scream “flagship feature” all over the place…).

The round carrying case is made of metal and quite large as well as heavy, but that is okay as the SIRIUS is not your everyday city car but more like a luxury sedan that is large and heavy as well.
The lid features a really nice Fidue engraving and the container is bolstered on the inside so the in-ears won’t get additional scratches over time.
A little drawback however is that the adapters have to be detached for storage, else the in-ears won’t fit inside (let’s hope this won’t lead to a connection issue over time).

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Comfort, Isolation:

What I expected was an in-ear that is comfortable and easy to insert and wear with a good over-the-ear fit (well, that’s usually no wizardry with my large and in-ear-friendly ears).

Well, this is where the SIRIUS disappointed me to some degree (using the stock tips). It is indeed on the quite large size, so having larger than average ears does come in very beneficial. In my ears, there is also still some space left and the A91 is somewhat smaller than my UERM custom fit in-ear monitors (but just slightly).
What I somewhat dislike and what causes some fiddling until I achieve a good seal are however the short nozzles. My ears are not only on the larger side but also quite deep. And for me, the SIRIUS would definitely benefit from longer nozzles, as it takes some time until I get an ideal seal (quite similar to my ATH-IM03). And although the fit is then not really uncomfortable, the edgy lower parts of the in-ears’ bodies’ exteriors touch my ears in my conchas and cause some sub-par discomfort which could have been avoided by somewhat more rounded edges on the outer side/faceplate and longer nozzles.
So it is about as uncomfortable as my IM03 and somewhat longer nozzles would have been very beneficial for people like me who have deep ears (people with not as deep ears should not be facing problems as the edgy part shouldn’t touch their conchas).
Using aftermarket tips might help with this, but I would have personally preferred a longer nozzle due to my “not a single aftermarket part/modification” philosophy when it comes to headphones.

With the guide-less and memory wire lacking cable design along with the MMCX connectors with threaded locking mechanism, it is theoretically possible to easily wear the SIRIUS with the cables down if one is into that kind of stuff.
But usually in the higher price range and professional sector, the cables are worn around the ears, which is also how the SIRIUS was most likely intended to be worn and how I am wearing it, like the vast majority of my in-ears. And due to the threaded locking collar of the MMCX cable, the connectors don’t rotate and the SIRIUS’ connectors are among the very few MMCX connections that I very personally also trust on the long run.
Microphonics are by the way extremely little and close to nothing.

Exterior noise isolation is rather on the weaker to average side compared to completely closed body in-ears, but that was what I kind of expected due to the vented hybrid design.


For listening, I used the Luxury & Precision L3 in balanced mode and the iBasso DX90, DX80 as well as the LH Labs Geek Out IEM 100 and last but not least Leckerton UHA-6S.MKII in single-ended mode.
For critical listening and comparisons to other in-ears, I used the DX90 and Geek Out IEM 100.

Although I am no burn-in believer with headphones, I burnt the A91 SIRIUS in for over 200 hours with noise as well as sine and music signals before I even started critical listening, just to be on the safe side.

For listening below, I used the largest size of the included silicone tips.


I surely had no idea how the SIRIUS was tuned, but a few presumed sound signature characteristics I had in mind were a smooth, musical and slightly warmed-up bottom end with a sparkling yet not overdone treble, an even and coherent sound along with some musicality and fun without neglecting class and maturity.

And it turned out that I was not too much off with my assumption although it turned out much more balanced than I expected – what I am hearing is a very moderate elevation in the bass that is however so far from being overdone and just slightly north of neutral, relatively balanced, and reaches quite deep but loses a little quantity in the lowest registers of the sub-bass. So there is enough sub-bass and it is there when called upon, but it is not the extroverted star of the show and takes a small step back compared to the upper bass and midbass. Upper bass has got a nice kick to it, with some slight smoothness and warmth in the lower root that however ebbs away quite soon so there is no spillage into the lower mids and no unnecessary added warmth in the rest of the root – just enough to make the low end appear musical yet not too smooth or warm.
The mids’ timbre is pretty neutral in my ears, with vocals sounding realistic and not coloured. Because of an emphasis in the lower treble, mids’ overtones have a slight upwards shift without tending to the coloured side in my ears though – it just adds some air without making the timbre shift to the unnatural side. Speaking about timbre, pianos and trumpets or saxophones don’t really sound altered but quite natural to me, as opposed to the UPQ Q-music QE80 (OEM of the Fidue A83) that shifts trumpets a little to the thinner side or the Audio Technica ATH-MSR7 where vocals’ overtones are on the slightly brighter side as well but where trumpets sound more like a squeaking noise.
The treble is somewhat more on the brighter side, with an even rising quantity from the lower to upper treble. I would not be surprised if there is some sort of countervailing dip in-between, as there is no edginess or unevenness and the treble is not obtrusive although it is somewhat emphasised, but I’ll find that out quite short when I do my sweeps. Air and extension past 10 kHz seem to be quite good and there is some nice subtle sparkle in the super treble past 10 kHz.
What kind of amazes me similar to the Q-music QE80 is that although the upper end is on the brighter side of neutral, it lacks sharpness or edginess and sounds coherent as well as easily tolerable. It is not yet as harmonious as the Etymotic ER-4S’s treble which is probably the most even treble I have come across but among the in-ears with a brighter upper end tuning, it definitely belongs to those with a very coherent and annoying-free character.
So overall, I would say the SIRIUS falls into the category of a slightly w-shaped in-ear that is very balanced sounding overall and slightly leans more towards the brighter side without being annoying at all.

Bass quantity by the way depends on how much the small vent is covered up by one’s ears. In my ears, it is not covered by that much, so it gives just the necessary amount of boost in the low-end so that the sound does not become boring but has a nice texture and musicality to it. Depending on your ear anatomy, the bass can be either more present or a little leaner. If you are into modding, you can of course also perform a tape mod to close the small vent in order to achieve more low-end quantity and impact.
Further below when I perform the sine sweeps, listen to noise and determine by how much certain frequency bands are boosted and by how much, I will be able to tell the bass quantity the SIRIUS has in my ears. My guess would be around 4 to 5 dB compared to a very flat in-ear like the ER-4S and probably 2 compared to the UERM.

So overall, one can definitely recognise some of Fidue’s hybrid in-ears’ house sound in the SIRIUS which has however matured, having less bass quantity than the A73 and UPQ QE80 in my ears, with less warmth in the lows, less root warmth and better extension towards the lowest sub-bass. Overall, it seems like the A83/QE80 was taken as base for the SIRIUS which was however tuned for a more balanced and mature, less fun tonality, with a more realistic timbre in the lower treble and less sibilance although I already didn’t have complaints at all with the QE80.
So yeah, it is quite a flagship-worthy tonality with an excellent balance between maturity, musicality and moderate fun.

Moving on to what I hear with the sine sweeps, noise and EQ counter-checking: from about 450 Hz down, the lows’ emphasis starts climbing, reaching the climax with being ca. 5 dB north of neutral compared to a completely flat in-ear at about 200 Hz, which is kept upright down to 35 Hz from where on it rolls somewhat off towards 20 Hz. This gives the sound some non-overdone impact and enough bottom end and lower root warmth not to sound sterile.
From 1.3 kHz on, level starts increasing up to 7.6 kHz where the treble emphasis’s climax is located at. From there on, it takes a slight step back without becoming dark at all and reaches up high past 17 kHz. Surprisingly, in contrast to what I assumed earlier, I am hearing no dip in the middle highs around 4 to 6 kHz, and the treble is still easily bearable, which is also because I don’t hear any peaks or dips in the highs, just a very even upwards slope.


Before having even received the in-ear or listened to it once, I expected a well-rounded and controlled bottom end with quick attack and slightly slower decay to create a nice, musical body while maintaining a good level of crispness and speed, along with a detailed midrange and treble without any harshness or annoyance.

What I got was mostly what I expected – hybrid flagship-like performance.
The bottom end is excellently controlled and quite quick and nimble. And it is not any soft at all although typical for the dynamic driver, attack and decay are not as quick as with most BA drivers (on a second note though, it beats some back-vented BA in-ears in terms of bass aridness, sounding less soft and better controlled). Contrary to what I expected, the attack has about the same speed as the decay and lacks a very slight bit behind the FLC8s’ dynamic driver’s speed, but what the SIRIUS still has got is some addictive yet not overwhelming at all bass body and tactility, which is the main reason why many people love a dynamic driver for the lows. And oh yes, the SIRIUS does such a great job down there, finding just the right balance between speed, body and control. It just handles fast Metal as well as Electronic music with great control as well as ease and has still got that dynamic driver’s body. On another note, I wouldn’t be much surprised if one of the five acoustic ways also contains a BA driver for the lows in addition to the dynamic drivers, as the bottom end is pretty clean and fast while still having that really nice body.
Moving to the mids, they are nicely textured and detailed, revealing small variances of the singers or multiple layers with an easy-going and smooth, highly detailed character. Because of the upwards slope in the treble, there is a little more of a favour of female vocals because of the more up-front overtones, but male vocals are no less detailed and layered.
Treble is excellent as well and although it is a little more on the bright side, it becomes never annoying and single notes are cleanly as well as precisely separated from each other.
Overall sound is highly dynamic and realistic, with really good fine detail retrieval.

And of course, everything sounds very coherent. I know there is still more possible resolution when going up in price, but one has to spend noticeably over $1000, close to 2000, to get a comparatively small sound quality increment when put in relation to the price (keep in mind that the higher we go in price, the more the law of diminishing returns kicks in).


I was expecting an open, holographic soundstage with good layering and authenticity.

The imaginary soundstage is indeed large, spacious and well-rounded. It is not as large as for example the UE18 Pro’s and not super wide, but very well rendered and rounded with precise instrument placement as well as really good separation, so the imaginary room is very tidy without instruments bleeding into each other what enforces the impression of a really nice and large appearing soundstage.
Overall, sounds are well detached and appear more to be all around the head.
Picking out the position of single notes, instruments or singers works pretty well and the soundstage has got a good forward-projection and sounds overall pretty realistic and – what I find most important – authentic, what so many in-ears in a lower price range do not achieve to the same extent. There is indeed some really nice air around instruments and notes.

Mission accomplished, the SIRIUS fulfils my expectations regarding sound.


In Comparison with other In-Ears:


UPQ Q-music QE80 (OEM Version of the Fidue A83):
As mentioned above, the SIRIUS seems like the more mature and grown-up version of the QE80.
The UPQ has got more bass quantity which is also warmer and shines a bit more into the root, giving a creamier and richer low-end. The QE80’s upper mids are somewhat more on the brighter side, along with the lower treble, making trumpets and pianos sound a bit brighter than they are (it’s just a small complaint though) – here, the SIRIUS appears more realistic. Moving on in the treble, the SIRIUS is somewhat less bright despite the QE80 having a narrow dip in the middle highs (which is only audible with sine sweeps though).
When it is about detail retrieval, the SIRIUS is definitely an upgrade: while the QE80 has got the more present body, it comes at the cost of speed and control in comparison with fast music, so the SIRIUS has got the better controlled and quicker bottom end. The SIRIUS’ mids are also better layered and textured, with the higher minute detail retrieval. In the treble, there is no major difference but the SIRIUS also appears slightly better separated despite being less bright.
The SIRIUS’ soundstage is somewhat wider while both have almost identical depth (the SIRIUS has a little more depth though). The SIRIUS’ soundstage is however better layered, textured and separated, with more precision and air between instruments, wherefore it sounds more authentic.
So yes, the SIRIUS is an upgrade to the QE80/A83 on the technical side and also more balanced sounding. Nonetheless, I still love the QE80 for its fun yet smooth and even/harmonious tuning.

FLC Technology FLC8s (red – grey – gunmetal   Filters):
The SIRIUS has got somewhat less bass quantity but a bit more warmth in the root. In the mids, both are quite comparable although the FLC8s is a little more forward here. In the treble, the SIRIUS is the somewhat brighter in-ear, especially in the middle treble where the FLC8s has got a dip.
The FLC8s’ bass has got the somewhat quicker attack while both have similar decay, control and precision in the lows. The SIRIUS on the other hand has got the more addictive and nicer body.
The FLC8s’ mids are more detailed and liquid, even more than my UERMs’, so here it even outperforms the SIRIUS by a little.
In the treble however, the SIRIUS sounds more realistic around 10 kHz and reveals more details, seems a bit more easy-going overall.
The SIRIUS’ soundstage is somewhat wider and deeper but not by much. The Fidue’s stage also appears a little better placed and authentic, while both have very comparable and precise separation.
Overall, both are quite close when directly compared. Here and there however, the SIRIUS is somewhat better albeit the FLC has got the more liquid mids.

DUNI DN-2002:
The DN-2002 has got the more forward bass in my ears but somewhat less sub-bass extension, however especially more root and upper bass quantity. The DUNU’s (especially lower) mids are somewhat more on the warmer and thicker side.
Both in-ears have got very comparable bass quality as well as control, and even the body is very comparable although the DUNU’s is more forward because of its higher bass quantity.
Moving on to the midrange, the Fidue’s appears slightly more detailed. It is a super close decision though.
In the treble, the SIRIUS is somewhat more easy-going and has got the more refined upper treble – again, it is a more or less close decision.
Going on to the soundstage, both in-ears have got comparable size but the SIRIUS generates some more air between instruments and therefore has the even somewhat more precise imaging.

Ultimate Ears Reference Monitors:
The UERM, while not being as flat as the Etymotic ER-4S when doing sine sweeps and listening to noise signals (as well as music), is still an overall very neutral in-ear.
Comparing the two, the SIRIUS has got somewhat more bottom end but really just a little. In the mids, both are comparable however in the upper midrange/lower treble, the Fidue has got the somewhat brighter overtones while both have got a relatively identical midrange timbre in my ears.
In the middle treble, the UERM has got somewhat less quantity. Moving to the upper treble below 10 kHz, the Fidue is a little brighter, but around 10 kHz, the UERM has got more quantity because this is where it has got its peak.
With its BA driver, the UE has got the somewhat quicker bass attack and decay and little better control, however it is surprising that the Fidue comes really close but has that typical dynamic driver body (nonetheless with excellent control and quality).
In the mids, both have got quite comparable details.
In the treble, the UE is a bit more detailed and better with craving out minute details and rendering them well. In the upper treble around 10 kHz, the SIRIUS is however a bit more authentic as well as realistically sounding (the upper treble has always been something where I felt the UERM could be a little more realistic, which is however criticism on a high level).
In terms of soundstage, the UERM scales a little better depending on the recording and has got more width as well as a bit more depth. Both create comparable air between instruments but the UE’s soundstage appears a little better controlled with fast recordings (supposedly because of the different woofers).
Overall, the UERM is still the somewhat more authentic in-ear, but the SIRIUS comes extremely close in most categories and has got the even somewhat more realistic appearing upper treble around 10 kHz to my ears.

Shure SE846 (white Treble Filters):
The Shure has got more sub-bass and a sub-bass emphasis. The SIRIUS has also got slightly less midbass and upper bass quantity and is therefore a little tamer in the lows and more balanced sounding (but then again, as written somewhere above, bass quantity will depend on how close the vents are to one’s ears). The Shure’s mids are somewhat more forward and a wee bit dark sounding to my ears. The SIRIUS has got the more even treble and especially better extension – above 8 kHz, the Shure is quite rapidly rolling off what causes cymbal crashes to sound somewhat cut-off.
In the bass and mids, both are really well comparable when it is about resolution. With its dynamic driver, the Fidue has got more bass body presence whereas the SE846 has got a very slightly better attack and control. Moving on to the treble however, the SIRIUS does not only sound more realistic (despite sounding brighter) and has got the superior extension but is also more detailed where the SE846 sounds a bit blunt in comparison.
In terms of soundstage, the Shure’s is a bit more on the smaller side compared to other $1k in-ears and CIEMs but no less precise, authentic and three-dimensional. While the SIRIUS’ soundstage is somewhat wider and deeper than the Shure’s, both have got pretty much identical authenticity, separation as well as air between instruments and appear similarly holographic.
If it wasn’t for the Shure’s somewhat sub-average treble, both in-ears would have been more similar than different (despite the different sound signature approach) on the technical side, but because of the upper end, I would definitely give the edge to the SIRIUS when directly comparing both.


I expected a flagship sound quality from the Fidue SIRIUS and this is exactly what I got.
The sound is excellent and definitely flagship-worthy. It feels like a more mature version of the A83/Q-music QE80 however it retains their musicality and has got Fidue’s unmistakable house sound that is however definitely more balanced.
Not much surprising and coming from Fidue, it does an excellent job of sounding relaxed yet somewhat bright and musical, but also very detailed and excellently controlled. It also does a great job of sounding moderately fun and musical although it does not drift away to sounding artificial or unnatural.
From the tuning to resolution, bass control and body, down to the spacious and well-placed and -separated, authentic soundstage, there is little not to like about the SIRIUS (as long as one is not into a warm and tendentially dark sound signature).
So Fidue’s aim was to create a flagship-worthy hybrid in-ear and that is what they exactly did with the SIRIUS – great tuning job, Mr. Benny Tan!
Where I however definitely see room for improvement is the design/functionality – the nozzle is quite short and might make it quite difficult for people with deeper ears to get an easy and immediate seal (I for example need some adjustment and fiddling until seal is good and as it should be) and the edgy lower section of the outer half/faceplate might also cause some discomfort (that’s what it does for me; more rounded outer edges and corners as with the UPQ Q-music QE80/Fidue A83 would have been much better if one is required to insert the SIRIUS deep in one’s ears – a workaround for those two fit/comfort issues could also be using aftermarket tips with a longer stem that might mostly resolve the issues). And although the cloth-coated cable is better than usual cables of that sort, it is still likely to fray over time and I think a braided/twisted cable as standard would have been better (in my humble opinion).

So while sound is excellent, comfort could be quite a lot better for me and for those who have large however deep ears, too.

With my usual 70% sound (97/100) to 30% quality/fit/comfort (in my ears with the stock tips) weighting, I come to a conclusion of 84.7% or 4.235 out of 5 stars, which makes close 4 when rounding it.
thank you for another superb review
I wonder if a set of triple flange tips (if any will fit over the nozzles) would help you get a better seal without having to have the shell so hard against your ears. Nice review Chris.

Sure, but they'd alter the sound, too. So far, I've found the stock tips to be the most harmonious sounding for me and my ears. The differences are subtle but most non-stock tips made the treble less even sounding for me and increased the upper mids, making them a tiny bit honky.

Foams were good but made the sound a bit warmer and fuller than with the silicpne tips and also changed the bass quality a little (well, basically the effect that foam tips give me with most in-ears).

I don't know, maybe a fourth (larger) size of the stock tips would be a not too bad idea to help people with large but deep ears get a nice shallow fit and seal.
Anyway, I'm personally also convinced that if a manufacturer wanted us to use other/different tips, he would've included them. I know I'm a little bit in the minority in the way of thinking so, but I'm an all stock guy.

So as long as I can get a sufficient seal and halfway secure fit, I'll take some discomfort and a 100% true and stock sound over a better comfort and probably slightly different sound with third party tips.


Headphoneus Supremus
Pros: Balanced midcentric signature, smooth and natural tonality, modular cable system, design
Cons: Extra weight of adapters, stage depth
I would like to thank Michael from Fidue for providing me with a review sample of the Sirius in return for my honest opinion.


Fidue is an established player with a loyal following, having made their mark in the entry level regions of the audiophile market with popular products like the A83 and A73. Now that they’ve conquered that market, it’s time for a step up. After years of intensive research, Fidue presents their new flagship: the A91 Sirius.

I didn’t get wind of any mission statement from Fidue about their new flagship. Something like ‘Fidue is challenging the status quo in the sub $1000 segment, with high quality sound for an affordable price’. I mean, something like that would make sense coming from a manufacturer that comes from operating in the lower regions of the audiophile market. But they didn’t have to. It’s visible in the product, and their choice of tuning – a well thought out signature that shows a certain refinement, and is very easy to listen to.

I’ve had a couple of 4+1 hybrids in the same price range in the past, and none of them really pleased me. They all felt like they were trying too hard, and lost a certain bit of refinement compared to the TOTL’s they were trying to be. With the Sirius, it’s different. It isn’t tuned to impress you with powerful bass, a forward midrange, or sparkly treble. Instead, the Sirius convinces with a smooth and balanced signature. It knows what it can do, and it does it with class.

Fidue A91 Sirius

-Drivers: Hybrid configuration with 1 dynamic driver and 4 balanced armatures
-Frequency range: 4 Hz – 45 Khz
-Impedance: 20 ohm
-Sensitivity: 113 dB
-MRSP: $899

Build & Design

I personally wasn’t a big fan of the A83’s looks, the red and blue plastic had more of a toyish feel than the allure of a high end product. How different with the Sirius – it truly is a masterful piece of design. The metal housing feels solid, and is in a distinguished dark gray color. It’s finished off with a slim silver lining around the edge, that I hadn’t noticed at first. Seriously classy; these have got to be one of the most beautiful universals I’ve seen. They are a bit on the larger side; I have medium/small ears so they fit me snugly, almost filling up the space like a custom. I get a good seal with the standard tips, but the bores don’t protrude very deep in the ears. I might have preferred to see them go a bit deeper, but overall I don’t really have any complaints about the fit and especially design. The cable connectors are MMCX, which I haven’t been much of a fan of in general due the sound cutting out on a regular basis with previous iems. But with the Sirius there’s an additional screw in red or blue to further fasten the cable. The system works well and feels solid, while ensuring a secure seal.


The Sirius comes in a matte black cube-shaped leather case that reminds me of the nice cases you get with high quality daps. When you open the lid, the shells are presented on the first layer with four pairs of tips pressed against bores in the case, along with a separate pair of complys. It further comes with some standard accessories like a ¼ inch and airline adapter, and a hockey puck style case I’ve been seeing before with the Galaxy and Primacy. The one that comes with the Sirius is a bit more ornamental, with some nice curves compared to the straightforward design of the others. But similar to those, it’s more functional as a storage unit for tips or random items floating on my desk, than as an actual carrying case for on the go.

But Fidue has packed along something really special: a modular system to use the Sirius with both balanced and regular sources. The cable is terminated in a 2.5 mm trrs jack for daps like the A&K or Onkyo players, but it comes with two adapters: one for balanced 3.5mm trrs players like my Plenue S and 901S, and a regular 3.5 trs for the rest. Balanced outputs are gaining in popularity, and alongside the high end daps more and more midtier sources have started to incorporating balanced outputs. It’s becoming the standard rather than exception, so chances are the modern audiophile will have one or more balanced sources. Incorporating the modular system saves having to buy a separate aftermarket cable, which would then be restricted to that source only. How thoughtful, and incredibly useful. 10/10 for the selection of accessories, I can’t think of a better total package I’ve come across.

But the modular system also comes with a downside. As is, the cable is already on the thicker side, especially below the Y-split. It’s a cloth-sheathed 8 core cable, and while beautiful, is also a bit heavier than a regular cable. The weight of the cable isn’t an issue for me, as I have an unnatural passion for 8 wire cables. So I’m used to it, and like the heavy feel as I associate it with quality. But since I have either regular or balanced 3.5mm outputs, I always need to use an adapter. The rhodium-plated plugs have a high quality look and feel to them, in the same color as the dark gray shells. But while the cable itself isn’t that heavy, the extra length and weight of the plugs tends to pull a bit while wearing them. So all in all the modular cable is a big plus, that comes with a slighter con.


Sound Impressions

The Sirius has a well-balanced signature with a mid-centric focus. A hint of warmth that adds an emotional touch to the music, without overdoing it. The instrument positioning is slightly close to the listener, with the vocals placed a bit further behind. Because of the proximal front line positioning spanning along the width, the stage has a bit of a ‘front row’ effect where you're close to the music. The instrument size is well proportioned within the stage; neither thick nor thin - just exactly right, which gives a nice sense of spaciousness. The stage is wide and has good height, creating an overall large screen. In my initial impressions with the Cowon Plenue S I found that the Sirius lacked some depth, but this is source dependent as the Lotoo Paw Gold provides more depth and air, at the cost of some of its width. On the other hand, the Sirius' tonality comes across as more natural with the warmer Plenue S, mainly due to a more prominent and brighter upper midrange with the Paw Gold.

The bass is fairly neutral, with a slight emphasis on mid- over sub-bass and an overall warm tone. The sub-bass is a pure delight. I spend most of my time listening to multi-BA drivers, so the gorgeous ‘thump’ of a dynamic driver is refreshing. That texture and decay - it’s with good reason people say a BA can never deliver that same type of quality. Kick drums sound magnificent, very realistic due to that decay. Not to mention bassy electronic music – possibly with the bass amped up a bit. I believe the proper audiophile terminology for this would be ‘awesome’. The mid-bass is well-controlled, although there is a tradeoff for speed compared to faster BA drivers. Overall the bass is punchy and textured with a natural decay, and I rate it highly.

The Sirius has a beautiful and sweet midrange, alongside the nicely textured bass. Slightly forward, but mostly balanced and refined - a tuning I liked from the go. The midrange is warm and smooth, with a natural timbre of vocals and instruments. In accordance with its mid-bass it has a slight lower midrange fill, giving the Sirius the right amount of note thickness without overdoing it. The midrange emphasis is on the upper midrange; guitars have good bite and vocals are clearly articulated, though not as deep or dense as a truly midforward iem as the S-EM6 or Zeus-XIV that have an emphasis on the center midrange. This gives the Sirius an excellent sense of balance, as vocals are neither particularly forward nor distant. The upper midrange peak is followed by a dip around 4-5 khz which adds some fullness to the presentation, adding to the overall smoothness rather than artificially brightening the midrange. Its midrange resolution is good within its price tier.

The treble takes a slight step back in the presentation, giving the Sirius a smooth and more mid-centric signature. A lower treble dip is followed by a peak around 7 kHz; a common tuning in many iems. It’s a necessity to add some clarity, especially in a mid-centric signature that might get too stuffy otherwise (we’ve seen this recently in the Primacy). The peak gives an iem a more ‘hi-fi’ sound, although there is a tradeoff for tonal naturalness at higher volumes. With a treble rolloff around 10 Khz, the Sirius performs according to the iem average. The treble is foremost smooth and non-fatiguing, and tends to stay on the safe side of sibilance. Overall, I’m a bigger fan of the bass and midrange; the treble is there doing its thing, but lacks that final bit of precision. This isn’t a treble that will bother anyone, but it doesn’t excite me much either.



Sirius vs Fidue A83 ($299)
The main question that might be on the mind of many of Fidue’s loyal followers: how does the A83 compare to the new number 1 in line. The Sirius has a wider and taller soundstage, creating an overall bigger screen. In addition, notes are proportionally thicker to the larger stage; the A83 has a more distant instrument positioning. Because both the stage and instrument size is bigger, the sound is fuller and overall more engaging. In addition, the Sirius has better instrument definition.

This fuller sound is due to the more forward midrange, while the Sirius also has more mid-bass emphasis compared to the A83. While the A83’s sub-bass is punchy with bass-heavy tracks, the Sirius has a higher impact overall. The Sirius has a warmer and more pronounced midrange, with more vocal depth; vocals have greater density, and the A83 can sound a bit hollow in comparison. The A83’s signature is tilted slightly more towards the treble, compared to the more mid-centric Sirius; this can make A83’s tone sound a bit metallic in comparison, with a greater tendency towards sibilance. Overall, the Sirius retains the smooth house sound of the A83, while improving in all directions.

Sirius vs. DN-2000j ($299)
The Sirius’ stage is slightly wider, but mostly taller. Both share a quality bass response with nice texture and a natural decay, although the DN-2000j’s has a colder tone compared to the relatively enhanced mid-bass of the Sirius. This gives the Sirius thicker notes and a fuller sound, although the DN-2000j’s stage is cleaner. Compared to the midcentric and more forward presentation of the Sirius, the DN-2000j’s tone is skewed towards the treble. This gives it a high sense of clarity and detail retrieval, while simultaneously making it sound thinner, with a less natural tone.
The Sirius and DN-2000j are tuned with a very different presentation, and overall have fewer similarities than differences. The DN-2000j presents music from an analytical perspective; the Sirius in turn, has a more natural, effortless and fuller presentation.
Sirius vs EarSonics S-EM6 ($950)
The S-EM6 is EarSonic’s contender in the same price range. While it also has a mid-centric signature, it is more midforward than the Sirius. The enhanced mid-bass plays a prominent role, giving a great deal of warmth and size to the midrange. The Sirius’ bass is more neutral and cleaner in comparison, while adding a natural decay from the dynamic driver. The S-EM6 has more of a center midrange peak (around 1kHz), giving vocals more depth and density than the Sirius. Vocals are forward and powerful, and truly the S-EM6’ specialty. Its signature is however tilted more towards the midrange, with less treble emphasis. This gives the S-EM6 a darker sound, taking some of the bite off instruments with a less airier sound overall.
The S-EM6’ stage has similar height and width, but is deeper. This gives the S-EM6 an advantage in its instrument positioning. However due to the thicker notes, the stage doesn’t necessarily feel more spacious compared to the cleaner and relatively more neutral Sirius. The S-EM6 is warmer, thicker and more forward in comparison, but this tends to make it more of a specialist. With its mid-bass and center midrange bumps, the S-EM6 is the equivalent of a curvy, bubblicious woman: there’s a whole lot to love, if it’s your thing - the enhanced bass and warmth won’t be for everyone. The Sirius is relatively more linear in the lower frequencies and cleaner in comparison, with a refined signature that makes it more all-round.

Sirius vs Perfect Seal AR6 ($950)
The AR6 is another great performer with a similar price, also utilising 6 BA’s compared to the hybrid Sirius. The AR6 has a more neutral mid-bass tuning, and greater emphasis on sub- rather than mid-bass. The AR6’ bass hits deep, but is overall lighter and less warm. The AR6’ bass is faster, but it can’t match the natural decay and overall impact of the Sirius. The Sirius’ has overall more bass impact with nicer texture. This contributes to Sirius’ warmer midrange with slightly thicker notes, while the AR6’ stage is cleaner and airier due to it having less mid-bass and lower midrange fill. The AR6’ treble in turn has more sparkle, while the Sirius’ is smoother.

The AR6’ unique selling point is its wide and airy stage; its stage dimensions are both wider and deeper with similar height, and an instrument positioning that is slightly more distant than the proximal placement of Sirius. The AR6 is more spacious, and has the upper hand in separation. While the two iems are very different, they both steer me towards easy listening, singer/songwriter type music. But they take a very different approach, with the AR6’ focus on clarity and sparkle resonating in acoustic instruments, besides its spacious stage. The Sirius on the other hand has that delicious bass, and enveloping warmer midrange better capable of conveying emotion.


Sirius vs EarSonics S-EM9 ($1490)
The Sirius has a slightly wider stage, while the box-shaped stage of the S-EM9 is deeper and airier which gives it an advantage in layering. Both the Sirius and S-EM9 share a bass tuning that is relatively neutral yet exciting; punchy, with good definition. While the BA driven S-EM9’s bass has the better speed, the Sirius brings texture and that beautiful natural decay to the table. The S-EM9 is pretty linear throughout the lower and center midrange, with a dip in the upper midrange giving the S-EM9 a more distant vocal positioning. The Sirius on the other hand has more lower midrange fill, while getting most of its energy in the upper midrange. This gives it better vocal articulation; vocals are more forward and pronounced than with the S-EM9. Due to its slightly mid-centric signature the Sirius also has the warmer midrange, with overall thicker notes.

The S-EM9 has a U-shaped signature with slightly enhanced treble. While the Sirius’ midrange is clearly the more lush of the two in both warmth and size, the S-EM9 displays its refinement in the tuning of its treble, midrange resolution and separation. The S-EM9’s treble extends further, and is more clearly defined. Furthermore the S-EM9 betters the Sirius in its overall speed, the attack and decay. While this gives the S-EM9 a more dynamic sound, it doesn’t say the Sirius underperforms; speed happens to be the S-EM9’s specialty, even compared to other TOTL’s. The Sirius gets points for its overall signature, the excellent bass and midrange. The S-EM9 in turn for its precision in timing and positioning.

Sirius vs Rhapsodio Galaxy ($1600)
As a somewhat ‘exotically’ priced single double dynamic driver, the Galaxy’s bass shares that delicious impact and decay of the Sirius, although the Galaxy’s bass is overall more linear compared to the slightly more enhanced mid-bass of the Sirius. In fact, the Galaxy’s signature is very linear from the bass on through the midrange, only to peak in the lower treble. In comparison, the Sirius is warmer with a more forward upper midrange. Because of this, the mid-centric Sirius sounds enveloping and smooth, while the Galaxy’s tone is skewed towards the treble.

The Galaxy has a more distant stage, with vocals positioned further back in comparison to Sirius. The Galaxy’s stage is slightly wider, but less tall, while the Sirius has a relatively more even proportioning between the width and height of the stage. The Galaxy has the better midrange resolution and cleaner separation due to the relatively more distant instrument positioning, although its stage is also not particularly airy. Taken together, the Sirius tends to pull you in the music with its enveloping midrange placed closer to the listener, with a focus on a natural and smooth tonality. The Galaxy’s presentation is more distant and flatter, although instruments are better defined with an overall higher level of detail.


Concluding thoughts

The Sirius has a slight mid-centric signature, but it’s ever so well balanced. The sound isn’t too forward or thick, while having the right amount of warmth to sound natural. The treble is inoffensive, which means it can be played for days on end. It’s a type of signature that drifts me towards band-based music, soothing guitars and beautiful vocals. Its tuning is very mature, and seems designed to please all types of listeners in the market. With the Sirius, Fidue has delivered an excellent addition in the sub $1000 segment. With its natural and smooth midrange it has its own strengths, even compared to higher end monitors. The delicious bass is just a bonus at this point.

Whether or not Fidue is publicly stating it, they are implicitly sending a message; high quality is possible for a (relatively) affordable price. They’ve shown they can do it in the affordable segment, and they’re taking it to a higher level now with their all new flagship. The modular system is a very nice extra. With the lower regions of the market covered, they’re coming for more. As a complete product, the Sirius oozes with class; the design, packaging and distinguished tuning.


Originally posted at
@Dillan and @Kerouac Thanks I appreciate that! The Sirius has a very nice signature that I think will be appealing for a lot of people.
@BartSimpson1976 You're referring to the balanced lines used in stage equipment, where the sending unit inverts the signal and the receiving unit sums the signals and eliminates the difference between them effectively reducing noise. That might have been the standard in 1976, but now balanced most commonly refers to the L/R separation of the channels by using a 4 pole termination instead of the standard 3 pole L/R/ground that shares a common ground. Completely separating the L/R channels most prominently affects stage dimensions and precision.
guess it depends on implementation. In the Onkyo it might make a difference as in balanced mode both DACs are utilized and one only in SE, while e.g. in the Opus also in balanced  both DACs are used. But generally balanced is way overrated for portable use although it might not be plain BS (unlike "burning in" or cable sound)
Well, the two channel ES9018K2M dac used in the Onkyo is usually implemented as using one for L and R separately. So I don't know how they could only use 1 of the dacs for SE or why they would even want to implement it that way. Even more so because the dac has very little to do with balanced if anything, as the output is done by the amplifier. This is for instance evident in daps with changeable modules like the Fiio X7 and Hifiman 901S. You change the amplifier for balanced, the dac stays the same.