Fidue A91 Sirius

INTRODUCTION

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?

ABOUT FIDUE
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

Fidelity
Inspiration
Durability
Uniqueness
Enjoyment.

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.

DISCLAIMER
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)


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.

THE REVIEW

PACKAGING AND ACCESSORIES
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 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 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 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.

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.

TECHNICAL SPECIFICATIONS
(From Fidue’s packaging / website)

Model	Fidue A91-Sirius
Approx price	$899 USD (Penon Audio)
Type	Five driver hybrid IEM
Driver - Dynamic	1 x 10mm titanium DD
Driver - BA	2 x Knowles dual BA (4 BA)
Freq Range	4Hz – 45 kHz
Impedance	20Ω
Sensitivity	113 dB
Cable	1.3m, replaceable (MMCX)
Jack	2.5mm rhodium plated balanced, straight – with adaptors
Weight	37g with default cable
Casing material	Anodised Steel

FREQUENCY GRAPH

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 matching	A91 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

BUILD

Internal side of the shell	Front (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 shell	Rear 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 cinch	2.5mm 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 adaptors	3.5mm 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 stunning	And 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

FIT / COMFORT / ISOLATION

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 good	My 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 nozzle	But 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.

SOUND QUALITY

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 + E17K	And 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 http://www.head-fi.org/a/brookos-test-tracks.

Relativities

• 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.

Strengths

• 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.

Weaknesses

• 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.

AMPLIFICATION REQUIREMENTS

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!)

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.

RESPONSE TO EQ?

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.

BALANCED VS SINGLE ENDED

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.

COMPARISON WITH OTHER IEMS

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)
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)
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)
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)
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)
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.

FIDUE A91 SIRIUS – SUMMARY

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.

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

Thanks @Tony-Hifi at www.hifiheadphones.co.uk for providing me the opportunity to submit an independent review of the Fidue Sirius A91 (I have no affiliation to either hifiheadphones.co.uk 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.    
 

 

Sound

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'.  
 
 

Conclusion

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.

 
 
              
 
 
 
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
 
Specs:
 

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

 
 
 
Packaging:
 
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.
 

 
 

 
 
 
 
Accessories:
 

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

 
 
Tonality:
 
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.
 
 
 
Bass:
 
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.
 
 
Mids:
 
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.
 
 
 
Treble:
 
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.
 
 
 
Soundstage:
 
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.
 
 
 
Conclusion:
 
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.