Symphonium Helios


100+ Head-Fier
Symphonium Helios - Mr Clean, for better or for worse.
Pros: Neutral, clean tonality;
Great treble response; and
Crisp and fast detail.
Cons: Rather hard to drive;
Awkward shells and long nozzles lead to odd fit;
Mid-bass/lower-mid dip creates some incoherency; and
Somewhat dry and unnatural tonality.


Many thanks to @Damz87 and @Sebastien Chiu for arranging the Australian tour of the Helios.
The sources used to form this review included:

  • Chord Mojo 2;
  • Shanling M6 Ultra; and
  • Luxury & Precision W4,
all fed with lossless FLAC files.

There are a number of nations that are associated with the manufacturing of certain products. There is something to be said about a German car, a Scottish whiskey and now perhaps, a Singaporean IEM. Singapore has emerged as a heavy hitter in the audio scene and more specifically, the IEM scene. Today’s review concerns the Helios by Symphonium, a fairly new entrant into the audio market that has made some waves with their trio of initial releases and their association with their compatriots, Subtonic and Nightjar. This trio of makers from Singapore have garnered some attention for their rather exciting releases into the IEM market. But is the Helios a flash in the pan or a foundational product for someone that expects to be a market-leading audio manufacturer?

The Factual Stuff​

The Helios comes in a rather spartan and compact box housing within:
  • Stock Symphonium tips;
  • AZLA Sedna Eartips;
  • An Altatune Audio Nova copper cable;
  • A nice authenticity card;
  • A cleaning brush; and
  • A handsome metal carry case with a screw down lid.

The earpieces themselves are an angular and oddly shaped piece of machined alumnium anodized in black and adorned with simple white text. Within these earpieces are four balanced armature (BA) drivers accompanied with a four-way crossover to help the BAs to work together nicely. The Helios also spruiks their Filtered Linear Attenuation Tuning (FLAT) which promises to avoid impedance mismatches and any impact that your source will have on the frequency response curve of your Helios.

You get all of this for the price of 1099 USD, placing the Helios against stiff competition in the fabled “kilobuck” region.


The Opinion Stuff​



The Helios takes a sub-bass focussed approach to the lower end of the frequency response curve, elevating the lowest of frequencies to provide a satisfying sense of presence with great extension and presence. The low-end makes itself heard in songs such as “Solar Sailer” from the Tron Legacy soundtrack and Jhene Aiko’s “B.S.” each providing a very satisfying sub-bass rumble. The Helios does not sacrifice quality however as these frequencies remain nicely detailed and textured.

The mid-bass on the other hand is rather anaemic in comparison, with this section of the frequency response curve being pulled back rather heavily, potentially in order to maintain the clarity of the mids (further outlined below). Subtle bass lines in tracks such as “Out of Time” by the Weeknd or “Above the Clouds” by Gangstarr remain discernible but removes an element of punch and impact. This definitely renders certain songs feeling thin and lacking that fun factor.

Overall, the Helios takes a rather safe approach to bass tuning to achieve, what I feel is neutrality and cleanliness throughout the entirety of the frequency response.


The shift from mid-bass to lower mids is a rather peculiar one with this region seemingly being recessed to the point of removing certain sounds in tracks that I am quite familiar with. The result is an odd presentation wherein there is a jump from sub-bass to certain vocals and instruments in the mids. I also believe that this dip is also responsible for a seemingly recessed male vocal line, as certain songs such as more Weeknd tracks and “Just the Two of Us” by Grover Washington & Bill Withers felt a little thin and lacking the emotional impact of the male vocalist’s voices.

The upper-mids seem to be tuned with greater gusto however, as female vocalists and higher pitched instruments felt much more present within the mix. K-pop is characterised by the airiness and heady voices of their female vocalists and that much is apparent when listening to the Helios. There is perhaps a little too much juice towards this end of the mid spectrum as some songs such as “4 walls” by f(x) and “Fine” by Taeyeon came off a little shouty at times.

The timbre of the mids is also a bit off by my listening as each note comes hard and fast, with seemingly little decay. The result is a little bit of perceived thinness and dryness in the vocal tonality. The benefit of this characteristic is a greater perceived sense of clarity in the region as each instrument felt very clear and crisp in its presentation.

Overall, the lower-end dip and upper-end boost seems to target a certain demographic and certain library of music. I feel that the mids are clear, crisp and nicely sparkly, but is somewhat unnatural in its presentation and potentially missing the note weight and emotional engagement that slightly warmer tuned IEMs would offer.


The Helios manages the treble region with great gusto, with piercing synths, harrowing violin solos and crashing cymbals providing a great sense of sparkle and crispness. Brushes on the hi-hats in “The Demon Dance” by Julian Winding present readily in the mix and are wonderfully visceral. Piercing synths throughout a variety of EDM songs were resolved resolutely by the Helios with each note being crisp and clear in busily produced tracks.

I do not find the treble peaky nor do I find it overly bright. the Helios manages to balance the treble rather well with the rest of the frequency response curve and the aforementioned speed of the Helios manages to replicate higher end notes with great gusto. Despite not finding it “overly bright”, I did find that it toed the line at times with grating synths in “You & Me” by Disclosure and remixed by Flume came across a little hot at higher volumes. With that being said, the Helios did not seem to cause me any fatigue over long listening sessions.

Overall, I found the treble crisp, fast and extremely well detailed. There is a very slight toeing of the line here but the hair-raising sparkle that certain songs provided on the Helios was very rewarding and I can definitely state that this is perhaps the most well executed portion of the tuning of the Helios and potentially amongst its competition. I cannot find fault in this region even if I tried and for someone with particularly "ded" ears in that treble doesn't immediately jump out to me on first listen, the treble was sorely missed when switching to other IEMs.


I’ve touched on it somewhat in my discussion regarding the tuning but the Helios appears to be a wonderful technical IEM. The crispness and speed of the 4BA setup combined with the tuning creates a wonderful sense of a highly detailed and greatly resolving IEM.

The aforementioned dryness of the notes may lead to certain notes being overly fast and slightly thin but speed at which the Helios runs through generously produced tracks is something to behold.

It remains layered, coherent (save for that mid-dip) and certain sounds and instruments are easy to pick out from the mix. This is a particularly strong point of the Helios, perhaps by virtue of that mid-dip, notes seem to appear out of nowhere and strike with authority and speed. This style of speed and detail lends itself to a more spacious staging experience as it feels slightly diffuse in presentation.

Soundstaging is rather unique in that the Helios feels quite wide as certain notes seem to extend out quite wide in the headstage. The depth is also decent but I feel that this is helped along by the aforementioned tuning choice leading to recessed lower mids creating a faux-sense of depth.


The tuning of the Helios is, in my mind, a mixed bag. The sub-bass is wonderfully executed, the mid-bass leading into the lower mids is a black hole essentially, upper mids are crisp and elevated and the treble is simply wonderful.

This ends up creating a rather disjointed reproduction of music (in the case of my library at least) as I felt throughout listening to the Helios that I was missing out on something and there was less toe-tapping and singing along with my tracks and more just pointing out technical details of certain parts of the song.

On that point however, the Helios is, technically, a great IEM. Resolution and detail is provided in spades but this is perhaps at the cost of some note-weight, tastefully executed decay and a warmer, more emotionally engaging tonality. But this is simply a preference of mine and you may feel that I talking crazy here.



One thought coming to my mind here namely lessons learnt after multiple DAPs, DACs and Amps plus headphones and IEMs is synergy! Hoping for the one and only holy grail Setup is maybe just a nice wish unless buying according synergy transducers and I don't believe even the best sources are an exception here. There's a reason why people are having multiple devices in parallel or reducing inventory and keeping only the ones with right synergy.

Chord Mojo 2​

I would characterise the Mojo 2 as a very, very slightly warm neutral tonality with a more natural reproduction of instruments and voices with no DSP enabled.

This presentation of music does not impart any coloured tonality on the Helios and provides simply more of the same in that the Helios is able to present itself as it was likely intended. The result of this is a technically proficient and somewhat sterile listening experience wherein the end-user is feeling the music come at them fast with loads of detail within.

The Helios with the Mojo 2 didn’t really elicit any specific emotions out of me apart from just an appreciation of how well it resolved. As such I do not feel that the two synergised with each other well in stock settings but after a bit of tinkering with the DSP to correct some of the perceived misgivings above, I felt the Helios improved due to a greater alignment to my preferences. I altered the mid-bass to give a little more oomph to the bottom end and add in to what I call the "fun factor" of the Helios.


Shanling M6 Ultra​

I would characterise the M6 Ultra (M6U) as a smooth, slightly warm source with an increased sense of presence in the mids and a strong note weight.

This presentation seems to work well with the Helios as it seemed to elevate that previously mentioned mid-dip and add in a greater sense of warmth and weight to the mids that was previously somewhat thin and dry. The elevation in mid-bass and the euphonic quality it imbued on the mids generated greater enjoyment of the Helios for me and I thoroughly enjoyed my time with the Helios on this source.

I feel that the two synergise quite well with one another but considering that the M6U seemingly counteracts the conscious choices of Symphonium to tune the Helios in a certain manner, leads me to believe I am missing the point of the Helios.

Luxury & Precision W4

I would characterise the W4 as a fast, well resolving and somewhat dry source. With a penchant for sub-bass and upper mids on the stock settings, the W4 is seemingly similar to the tuning choices of the Helios.

These elements lead to a rather poor synergistic choice in my mind as it seemingly highlighted some of the issues that I had with the Helios as mid-bass remained rather limp, the mid-dip was left alone and the upper mids/treble started to venture into slightly too hot territory.

DSP settings such as the NOS digital filter and some other tweaks alleviated this but overall, I do not feel this represents the best choice for the Helios.


vs Campfire Andromeda (2019)​

A perennial contender in the kilobuck category, the Andromeda is characterised as a warm-neutral IEM with a rather generous amount of mid-bass and a euphonic, emotional presentation of music helped along with its unique staging capabilities.

Tonally speaking, the Andromeda and the Helios are chalk and cheese as far as I am concerned. A-B’ing the two is a rather grating experience as the Andromeda is seemingly muddy and incoherent at first listen but over time my ears seem to settle in and begin to note the lusher and more relaxed vocal presentation. Sub-bass is a definite win for the Helios whilst mid-bass on the Andromeda edges out a win purely based on my own biases as one could say the mid-bass on the Andromedas are muddy. For the mids, the Andromeda gets the nod from me as I prefer a warmer and more emotionally engaging presentation of vocals despite the loss of the speed and crispness in instruments. This is more of a nod from my own coloured tonality preferences and looking it from an “objectivist” point of view, the mids on the Helios are more detailed and resolving than the comparatively ‘muddy’ Andromedas. The treble on the Andromeda ventures into overly safe and I feel that I am missing out on the detail and extension of the Helios.

Technicality wise, the tuning would have you believe the Helios is the definite winner but on closer examination I do not believe one is a readily apparent winner over the other. The Andromeda’s warmth does detract from the sense of perceived detail in that notes do not jump out at you but overall it appears they resolve as well as the other upon a critical listen.

These two are heavily contrasting and I feel that I cannot give a definitive nod to one or the other from as objective as a perspective that I can give.

vs Sony IER-M9​

Perhaps the old-guard of the kilobuck region, the IER-M9 presents a slightly warm leaning neutral tonality and great technical ability but at the cost of coming off as a little too safe.

Comparing the IER-M9 and the Helios demonstrates some definitive differences. The IER-M9’s bass is, in my opinion, better balanced than the Helios with the exception for the detail within the sub-bass. The IER-M9’s bass chops as a whole cannot be denied and feels wonderfully meaty and present in every song that I listen too whereas the Helios flexes its muscles whenever there is a sub-bass focussed track on the queue.

Male vocals are better executed on the IER-M9 and instruments such as an acoustic guitar comes across as more natural and more engaging on the IER-M9 than on the Helios. The upper mids leading to the treble on the IER-M9 are slightly reigned in from the Helios but the result is a perceived loss of some sparkle and detail in the upper end. The extended treble of the Helios wins out in this regard compared to the IER-M9 as I felt it was much more well executed and had a greater sense of air and presence.

Technicality wise, the IER-M9 performs quite well on the detail and resolution front but I feel that staging is a little more confined and intimate on the IER-M9 which some people may like but others may not.

I feel that the IER-M9 takes a safer approach to tuning and provides similar technical capabilities. The warmth of the IER-M9 may have some detractors but I feel that it provides a more palatable tonality and does not lean too hard into the detail at all cost camp that the Helios seemingly occupies.

Overall, the Andromeda takes the most coloured tonality and is likely to be the most divisive tonally. The IER-M9 takes the safest route in my opinion and is a rather safe albeit boring choice in the kilobuck region. The Helios occupies the other end of the spectrum in that its tuning seemingly favours a more clinical approach to music reproduction.

Quality of Life Concerns​

The Helios are weird looking. There is no dancing around it, the angular housings combined with the long nozzles create a bit of a kerfuffle with fit. I for one, have had difficulties in finding an IEM which didn’t fit my cavernous earholes but the Helios took some adjusting and fiddling around with to get to fit well. The included cable did not feature earhooks and for good reason, these may protrude slightly and the cables may stick out and above your ear.

The Helios are also rather difficult to drive, requiring a rather healthy amount of juice to be taken to robust volumes. In my testing the W4 had to be cranked up to 70/100 on high gain through the balanced output to get it to border on slightly too loud which is rather a significant amount of power in my experience with IEMs.

The accessory package is half decent but the case is a screw down one that makes a godawful racket and the case is rather cramped if you’re not using the stock cable. I would have preferred a slightly larger case that wasn't made out of metal but I cannot deny it looks very, very nice.


The kilobuck IEM is an often-fabled price bracket with numerous competitors vying for dominance. There is something to be said for IEMs in this region as there is a great level of technical capability and a wealth of options for tonality. At the price that Symphonium is asking for, I honestly believe that the Helios is a fair purchase when viewing it from an empathetic mindset. The only question in my mind is the tuning. Some may value this detail-orientated and crisp IEM but I for one would rather either the IER-M9 and the Andromeda (noting that I am inherently biased as I paid for these two).

These two kilobuck IEMs offer up a more warm tuning approach and the three could sit on a spectrum with the Andromeda occupying the most coloured tonality in terms of warmth whereas the Helios sits at the other end in the cold, slightly clinical approach. The IER-M9 is warm indeed but sits in the middle of the two being the most balanced in my mind. So it really boils down to what tonality you enjoy but all three offer up their own benefits. Are you a treble head? Helios. Are you a bass-head? IER-M9? Are you just looking for something with off-kilter tonality and a warm and euphonic production? Andromeda.


“Objectively” infallible, the Helios tries to present a very clean and resolving tonality and achieves it with gusto. Instruments and vocals are clearly separated and the 4BA set up resolves extremely well, providing a crisp and “neutral” tonality.

“Subjectively”, the Helios presents a tonality that is too clean for me and dry in its presentation. Verging on the very edge of being unnatural for me, the Helios’ mid-bass/lower-mid dip as well as the sub-bass boost presents an oddly sterile tonality with certain instruments being thrown into the abyss in order to cleanly separate mids and bass.

I understand the appeal of the Helios for those looking for detail by any means necessary as the tuning seems to emphasise the idea of resolving notes in integral portions of the frequency response curve at the cost of everything else. The result to me at least, is a tonality that I feel fails to engage me emotionally and invites critical listening for random details you feel that you might have missed with lesser IEMs instead of simply relaxing to enjoy your library.

It is a fine IEM, but it is not a kilobuck revelation nor is it something I would welcome into my rotation based on subjective preferences. On my worst days I described the Helios as clinical and sterile. On my best days, I described it as wonderfully resolving, fast and crisp in its precision. The Helios, for better or for worse, is the Mr. Clean of the kilobuck realm and if that is what you’re looking for, then look no further.

This review and the rating I give it is inherently coloured by my own personal preferences but I've made it a point to try and highlight the strengths of the Helios which may have a greater weighting in your personal listening experience. Should you place greater weight on treble response and the crispness of note reproduction, then you may be more forgiving to the Helios.

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One of the best reviews I have read in a long time. Keep up the good work!


Headphoneus Supremus
Symphonium Helios - Classical Beauty
Pros: + Beautifully neutral tonality
+ Extended treble
+ Deep and tactile bass response
+ Laser sharp note definition and imaging
Cons: - Challenging fit
- Midbass dip
- Doesn't quite match the resolution and soundstage of top performers of its era
- Modern $500-ish IEMs are catching up
If you read this review, chances are you are passionate (and geeky) about IEM and personal audio in general. As a passionate enthusiast, at one time or another, it’s likely that you have the dream of making a great IEM that embodies your ideal sound so that the world can hear it. Whilst that dream remains a dream for many (including me), some of the geekiest and the most passionate members actually crossed the chasm and made their ideal sound a reality. Previously, we looked at tgx78’s Serratus and RikudouGoku’s Grand Alter Saber 2. Today, we look at Helios, the result of a collaboration between two boutique powerhouses from Singapore: Symphonium and Subtonic.


You can also watch my review on YouTube here:


  • What I look for in an IEM is immersion. I want to feel the orchestra around me, track individual instruments, and hear all of their textures and details. I’m not picky about tonality, as long as it does not get in the way of immersion.
  • I rate IEMs within with a consistent scale from 1 (poor) to 3 (Adequate) to 5 (outstanding). Ratings are assigned by A/B tests against benchmark IEMs, regardless of the retail price.
  • Ranking list and measurement database are on my IEM review blog.
  • Terms used in my reviews are consistent with the glossary by Headphonesty
  • This review is possible thanks to the Australian tour arranged by @Sebastien Chiu and @Damz87 (Thank you!). I have no affiliation with or financial interest in Symphonium. The unit retails for $1100 at the time this review was published.
Sources for listening tests:

  • iBasso DX300 (for all A/B tests)
  • FiiO K7
  • Hidizs XO
Local FLAC files ripped from CDs or bought from Qobuz were used for most casual listening and A/B tests. My playlist for A/B tests can be found on Apple Music here.

All of my listening was done with the stock Azla Sedna Earfit Standard tips. I listen at a medium volume. I usually turn up the volume until the midrange is fully audible and detailed, unless a treble peak or overwhelming bass prevents me from doing so.


  • Driver: 4BA drivers, 4-way crossover
  • Connector Type: 2-pin
  • Impedance: 8.5Ohms@1kHz
  • Sensitivity: 104dB/Vrms@1kHz (83.3dB/mW@1kHz)

Build and Accessories​


My first impression of Helios was the size of the box: it’s simple and tiny. Upon opening the box, I was surprised once more: the metal carrying case of Helios is also tiny next to leather round cases that usually come with IEMs from 64 Audio, Fir Audio. The tiny box and carrying case stood in stark contrast against the huge earpieces.


Before moving on to the earpiece, let’s talk about the rest of the accessories. Helios came with a cable that deliberately does not have any ear hook to help you wear the IEM more easily. At the bottom of the box, you will find a drawer that contains two types of ear tips and a “thank you” note with signatures from folks at Symphonium. I find this card to be a nice touch.

With accessories out of the way, let’s talk about the elephant in the room: the earpieces.


I’ll not sugarcoat it: Helios is a difficult-to-wear IEM. It’s not the sheer size of the earpieces that are troublesome, because the earpieces usually “float” outside rather than resting on the conchas of my ears.

No, most of the challenge of Helios comes from the thick and long nozzles. So long that I can wear the IEM at not one, not two, but three different insertion depths, which result in three distinct presentations.

How to wear​

The manufacturer-approved way or wearing Helios is deep-fitting. By deep, I mean Etymotic-like deep, with the nozzles going pass the first bend and the shells sit against the conchas of your ears. This configuration showcases the oft-cited treble extension and clarity of Helios in all of their glory. Great treble extension means tack-sharp imaging, strong sense of layering of instruments from closer to further away, and excellent sense of space due to how clear the reverberation of the recording venue comes across. This configuration also gives an extreme level of noise isolation, similarly to wearing an Etymotic IEM. There are but two drawbacks: soundstage feels narrow (less left-to-right extension), and this fit can be very uncomfortable.

At the other end of the spectrum, you can opt for a shallow fit by using larger tips. In this configuration, the eartips create a seal with the opening of my ear canals, meaning the nozzles of Helios barely enter my ear canals. This configuration gives me the widest soundstage and the most comfort. However, it introduces peaks and harshness to the treble region, which seem to impede my perception of upper treble. I find the sonic quality to have a noticeable downgrade.

My chosen way or wearing Helios is medium-deep fit. It means I used a medium ear tips and twist the IEM into place, similarly to Symphonium’s instruction. However, I stop when the nozzles reach the first bend. This configuration gives me the median between the two extremes mentioned above in terms of sonic quality, the width of the soundstage, comfort, and noise isolation. The rest of this review is based on this fit.


Frequency response of Helios against Variations and the Harman in-ear target. Measurements were done with an IEC-711-compliant coupler and might only be compared with other measurements from this same coupler. Visit my graph database for more comparisons.


It is helpful to think of an IEM as a filter that highlights or subdues different parts of the incoming audio signal. This effect can be measured objectively by the squiggly lines above, called Frequency Response (FR) graphs, which measure how loud an IEM is at different frequencies from 20Hz (bass) to 20kHz (upper treble). Subjectivity is how your ears and brain interpret the effect of that filter on your music and decide whether it is “enjoyable.” There are some “rules of thumb” when it comes to tonality, but most interesting IEMs usually bend the rules masterfully.

One of my favourite ways of looking at an IEM is to compare the vision of its creators with the end result to see if their lofty ideas can be translated to the reality. Symphonium envisioned the Helios to have “an exceptionally clean sub-bass punch that hits hard, without coloring the clarity of vocal presentations,” and “a smooth and detailed midrange” with “class-leading treble extension.” You can also find out more about the idea behind Helios from an interview with Toranku and Ken from Subtonic and the details about Toranku’s frequency response target.

So, how does Helios sound?

I would say it matches the vision precisely. The tonality of Helios can be summarised as “U-shaped”. It means:

The midrange is neutral or “flat.” In other words, Helios aims to disappear from the music instead of imposing an opinion on how the music should sound. It means that Helios presents instruments and vocals as-is rather than injecting additional warmth to make them more mellow and enjoyable. At the same time, Helios does not boost the upper midrange to the degree of other “neutral” IEMs like Moondrop Blessing 2 or Etymotic ER2SE. As a result, female vocals are not overly forward or “shouty”.

Is neutral tuning always good? Logically, an IEM that presents music without any colouring is ideal (a.k.a., “as artist intended”). Subjectively, the value of a neutral tuning depends a great deal on your preference and even your mood. I personally prefer IEMs to have very little colouring to maximise their compatibility with different music libraries and source chains.


The treble of Helios is carefully boosted. Much of the treble energy of Helios are focused in the upper treble region which plays a significant role in creating the so-called “technical performance” that I always look for when trying an IEM. Emphasis in upper treble allows Helios to create ambience embedded within recordings. For example, when I listen to “Bach’s Violin Sonata No.1 in G Minor: Presto” by Kavakos, I can easily hear the reverb of the violin within the recording venue, which improves the sense of space and the illusion of “being there.”

The mid-treble (body of cymbals and hats) is present but not overly emphasised. It means I can discern cymbals, hats, and chimes without much effort, but these instruments do not become too loud or piercing. Helios also does a good job at reproducing textures and nuances of these instruments.


The lower-treble or “presence” region is slightly subdued to control the harshness and avoid masking the upper treble. This tuning approach generally works. I did not find any harshness or sibilance despite the brighter tuning of Helios.

It should be emphasised that all of the treble niceties described above require a medium-deep fit. The treble would be harsh and not very detailed if you wear Helios with a shallow fit.

Let’s switch our attention to the bass region of Helios next.

Bass and Dynamic​

A good pair of IEMs/earbuds/headphones should be able to convey, even emphasise, the sense of rhythm and the ebbs and flows of music. In general, this energy requires IEMs to be able to convey rapid volume swings on the downbeat of an orchestra or the leading edge of bass note. It also requires tactile physical sensation of the bass, and the sense of rumble and texture accompanying the bass drops. An IEM can have loud bass, but still fail to convey energy should it lack other features above.
The bass of Helios is interesting in many ways.

The bass tuning of Helios can be described as “sub-bass emphasis.” It means that Helios can produce a sense of physicality and tactility. You can feel the pressure of kickdrums and electronic bass. This physical sensation makes listening to Helios fun.

However, Symphonium and Subtonic decided to cut the mid-bass region of Helios in order to avoid the bass from colouring the midrange. It means that you can feel the bass but sometimes, you cannot quite hear the bass. This tuning creates an inconsistency in terms of how Helios reproduces bass. If a track is mixed with a lot of sub-bass, you would find that Helios is a bassy IEM. However, if a track focuses on mid-bass, you would find Helios thin, light, and somewhat hollow in the bass.


On the plus side, Helios is very adept at reproducing transients: the rapid swings in loudness in music, generally at the beginning of bass notes or downbeat or an orchestra. For example, when I listen to “Let the Battles Begin!” by Square Enix Music & Nobuo Uematsu, I felt a clear sense of marching rhythm thanks to how “snappy” the Helios is. It should be emphasised that having large bass does not necessarily translate to great transient response. It’s quite common to find big but woolly bass even from IEMs with a sub-bass emphasis tuning.

Soundstage Imaging​


Stereo imaging or “soundstage” is a psychoacoustic illusion that different recording elements appear at various locations inside and around your head. Your brain creates based on the cues in the recording, which are enhanced or diminushed by your IEMs, your DAC, and your amplifier. Some IEMs present a wide but flat soundstage. Some present a “3D” soundstage with layering, depth, and height. In rare cases, with some specific songs, some IEMs can trick you into thinking that the sound comes from the environment (a.k.a., “holographic”)

When you use a shallow or medium-deep fit, you would find Helios to have an unusually wide soundstage. It means that the louder instruments and voices that are placed at the center of the stage would be pulled away, slightly outside your ears and your head. If you opt for a deep fit, then this advantage would disappear and Helios would have a stage width of a normal IEM.

The depth of the soundstage of Helios is good, but not as unusual as the width of the stage. I can hear a clear contrast between closer and further away elements of a mix when they play at the same time. There is also a strong separation between the highlighted elements at the center of the stage and the background, such as audience cheers or reverbs. However, Helios does not produce a strong illusion that the sound coming from the front of the head.


The precision of the instrument placement of Helios is excellent. A good way to think about the imaging of Helios is to think of a camera that focuses properly. Every element of a mix is placed at a precise and stable position with clear boundary, making it easy to track it. Things were more challenging when instruments and vocals are placed at the same position on the stage. Helios can produce a decent sense of layering, preventing them from mushing against each other, to a certain degree.

Soundstage imaging with games (CS GO Gameplay by Throneful) The pinpoint accuracy of Helios translates to gaming. It is easy to pin point both the direction and distance of the sound. If you have the skill, you would be able to take advantage of this ability.



Resolution is a fascinating subject due to the difficulty of pinning down what it really is. To me, “resolution” can be broken down into three components: (1) Sharpness, incisiveness, or “definition” of note attacks (see the figure above). (2) The separation of instruments and vocals, especially when they overlap on the soundstage. (3) The texture and details in the decay side of the notes. The first two give music clarity and make it easy to track individual elements of a mix. The last provides music details and nuances. Smooth and well extended treble response plays a crucial role.

Thanks to the snappy transient response and pin point imaging, Helios has excellent clarity and definition. Every instruments and vocals have clear boundaries. Percussive notes start cleanly with crisp attack. So on and so forth. The only time when Helios stumbles is when instruments and vocals overlap each other. This problem indicates some limitations on the “true” resolution of Helios and where Symphonium can improve.


Another area where Helios is simply good, not great, is micro detail. The best way to discern and highlight the difference between micro details of IEM is by listening to sparse but detail-rich recordings like “Bach’s Violin Sonata No.1 in G Minor: Presto” by Kavakos and the texture and nuances around the violin notes. IEMs with stronger midrange resolution can preproduce more information down to sound of the bow gripping the strings. Helios has a dry, even rough, texture in the way it presents the midrange, so it does not feel overly smoothened, but it does not resolve down to the level of some stronger performers.

Does it matter?

It depends. Those little bits nuances and details would appear everywhere across a complex recording, making the music richer and more vibrant in detail. It is particularly interesting when you do nothing but listening to a recording closely. But for certain genres and listening situation, I would say Helios is “enough.”

Source Pairing​


Helios is difficult to drive.

Similarly to Final Audio E5000, Helios has an annoying combination of low sensitivity and low impedance, meaning portable amp likely run into current issues. In fact, I managed to shrink the soundstage and reduce the dynamic of Helios, even in the shallow fit position, using a tiny DAP and the BTR5. I recommend using balanced output from the most competent dongle in your collection. If you have a desktop amplifier or a battery power amplifier like Topping NX7/G5, use them to get the most out of Helios.


Moondrop Blessing 2:

  • The tonality of Blessing 2 feels more “V-shaped” comparing to Helios
  • The violin sound of Blessing 2 feels more smoothened. It has less crunch and texture than Helios
  • The reverb trail of Blessing 2 is less defined.
  • The separation between the violin and the reverb at the background is not very strong. Everything feels more meshed together.
  • Helios has stronger definition and separation of voices. For instance, the female voice on the right side of the stage in Jolene (feat. dolly Parton)” by Pentatonix is crystal clear and easy to follow without effort with Helios, but harder with Blessing 2
  • Each voice also has more nuances and micro details with Helios comparing to B2
CFA Andromeda 2020:

  • Andromeda has much more lower midrange, so at a glance, Helios seems more separated. However, close inspection found that all voices are equally well defined and easily followed with both IEM.
  • The violin sounds richer and denser on Andromeda, but with equal level or slightly less textured and nuanced.
  • The reverb trail of Andromeda is similarly defined and easy to discern.
  • The reverb of Andromeda forms an arc or dome around the head. Helios feels more like listening to a two channel system.

64 Audio U12T:

  • The tonality feels more “U” with U12T: thicker lower string, and very high notes are more highlighted.
  • The kick drum is noticeably louder on U12T
  • The cymbals are noticeable louder on U12T
  • U12T presentation feels warmer and denser, like more “things” happening in the space between instruments and instruments have more body.
  • The violin sounds richer and denser with U12T, and at the same time equally or to slightly more textured and nuanced.
  • The reverb trail is the most defined.
  • The reverb forms an arc or dome around the head with the violin sitting in front, in the middle of the stage. Helios presents like a two channel system.
  • Helios has similar separation with U12t, even though the thinner midrange of Helios might make it seems like there is more space between instruments.
Symphonium Meteor:

  • Kick is noticeably louder on meteor
  • The overall presentation and tonality is thicker and warmer, like instruments and vocals have more weight
  • The depth of the stage is on Meteor side
  • The width of the stage is on Helios side
  • The definition of instruments and vocals are crisper and cleaner on Helios side. The cheers of the audience, for example, is more clearly defined with Helios.

My TakePermalink

Symphonium Helios reminds me of the contrast between “Classical” and “Romantic” beauty described in one of my favourite books, Zen and Art of Motorcycle Maintenance by Robert Pirsig. The romantic beauty is about the surface aesthetic, about the feeling, about looking at a “thing” as a whole. The classical beauty is about the underlying form, the balance, how parts fit together to form the whole. Most audio gears are, of course, romantically beautiful. With Helios, however, I see the classical beauty in how it was optimised, from the choice of tuning to the constraint in terms of the number of drivers being utilised.


Is this IEM for everyone?

No. The fit is difficult, and the dip in the lower midrange and midbass might alienate listeners who wants some extra warmth and thickness to their vocals and instruments. But if you know that you are after a reference and clean sound and you don’t have much problem with fitting IEMs, Helios is worth consideration.

Absolute Sonic Quality Rating: 4/5 (Great)

Bias Score: 4.5/5 (I like this IEM)


  • Beautifully neutral tonality
  • Extended treble
  • Deep and tactile bass response
  • Laser sharp note definition and imaging

  • Challenging fit
  • Midbass dip
  • Doesn’t quite match the resolution and soundstage of top performers of its era
  • Modern $500-ish IEMs are catching up

Updated: August 27, 2023
Smirk 24
Smirk 24
Yes and the OG has a more special treble than the SE IMO though both are fantastic.

The fit on the HSE is much improved and it’s a bit warmer/less clinical in the mids, though I felt this came at the cost of a slightly more congested soundstage.
There is only one problem with the SE: the newly released Crimson :dt880smile:
The crimson is worse sounding than the SE


100+ Head-Fier
Best Kilobuck IEM?
Pros: 1. Magnificent treble response
2. Superb bass for an all BA set (best I have heard!)
3. Solid technical performance and detail retrieval for the price (better than what you pay for!)
4. Outstanding staging and imaging at its price range
Cons: 1. Shells are on the larger side but fits well enough
Founded in 2015, Symphonium is a relatively new IEM brand from Singapore. Currently they are offering only 5 models on their website, Helios being the flagship costing $1099. Since its release, Helios has been receiving lots of praise and accolades everywhere which is well deserved in my opinion. Alongside its strengths, it does have a few drawbacks that I will discuss as well. Let's dive in.

Disclaimer: I am posting this review as a co-reviewer at Amplify Audio Reviews, a passion project by my friend Mr. @Sajid Amit . You can check out his videos at Check out the video review of Helios - . Also follow our Head Fi thread for latest discussions - There are no external incentives and all thoughts and opinions are of my own. Thank you!

Specs, Build quality and Accessories, Comfort:​

Helios is a pure four driver multi BA IEM, designed in collaboration with Subtonic (the guys behind $5300 Subtonic Storm which took the ToTL IEM scene by storm a few months back, no pun intended). It has a four-way crossover and uses high quality components from Panasonic and Vishay.

Helios comes packaged in a fairly plain looking black cardboard box but I am impressed with the bundled accessory package. Symphonium provides two cases, a hockey puck styled metal case with brand logo CNC’d on top and a small leather pouch. The pouch is only big enough for storing tips and cable though. Although weighty and extremely well built, I wish the metal case had a wee bit more space inside. The 4.4mm 26 AWG copper cable is well made and feels high quality when wielded. Fairly lightweight and doesn’t tangle at all. Alongside regular silicone tips, Azla Sednaearfit tips are provided as well which I find quite generous.


Comfort is fine. Helios sports two heavy and large metal earpieces (T6 Aluminium shells) and the nozzle is on the larger side. I have large ears and rarely encounter comfort issues with IEMs (even IER Z1Rs are very comfortable to me) so Helios gave me zero headaches in terms of fit and comfort but I think they might pose potential comfort issues for people with small ears. I would suggest doing your own research before buying in case you are someone who generally has fit issues with large earpieces. Demo them from a friend first if possible.


Build Quality - 5/5
Comfort - 4/5 (for medium large/large ears)
Accessories - 5/5

Sound (Basics):​

Symphonium Helios is something that I would describe as sub bass boosted neutral. The people behind Symphonium are good friends with fellow Singaporean boutiques Subtonic and Nightjar acoustics and they share R&D. Helios actually has a lot in common with 5x expensive Subtonic storm. In supercar terms, if Storm is the Porsche 911 GT3RS then Helios is Carrera T if that makes any sense.

I want to draw attention to the bass response first because I think bass, especially sub bass, is actually one of the strongest points of Helios which is often overlooked/ not given enough attention in most reviews. Helios exhibits almost non-existent BA behaviour when it comes to bass response and most people will have a hard time distinguishing the bass from single DD sets unless they get very clinical or have generally discerning ears.

Rating: 9/10

Midrange is clean and detailed as opposed to being lush and meaty. People coming from thick and overly smooth midrange might perceive the midrange as slightly thin initially. The razor sharp notes give a sense of incisiveness and transparency to both male and female vocals. I find the Helios to be favouring female vocals over male vocals though. Male vocals are not bad or anything per se, they are still very good but I think the relatively leaner lower mids takes some grunt off them. I have observed no significant upper midrange shout but female vocals can get a bit gritty/shimmery in rare instances. Overall though, I am quite satisfied with the midrange of Helios.

Rating: 8.5/10

Treble is where Helios absolutely nails it and trades blows with IEMs costing several times more. It is smooth and linear with brilliant extension all the way up to the air frequencies. Every instrument in the treble region sounds sparkly and razor sharp without ever becoming hot or splashy. There is some peak around the low mid treble frequencies but that rarely becomes bothersome. If you are someone who likes classical music and listens to a lot of string/air instruments or a rock/metal fan particularly nitpicky about cymbals and high hats then you are going to absolutely love the Helios.

Rating: 10/10


Sound (Technicals):​

Symphonium Helios is a technical powerhouse. If you are into raw details then Helios will not disappoint. However, almost all kilobucks in this range have very good detail retrieval anyway so I will not gush over it too much. Imaging is extremely precise and warrants at least a 9/10 rating. Timbre is great although there are IEMs in a similar price range that have better timbre such as IE900 and M9 for example but Helios is not too far off.

Separation and transparency is where Helios stands out the most in my opinion as far as technical performance is concerned but that comes at the expense of losing some note weight; can’t have ‘em all I guess. Soundstage is above average in its price range. In fact, I think only the UM MEST MK2 and IER Z1R have larger soundstage than Helios in the sub $2000 range and both of them cost significantly more. If you are planning to watch movies or play competitive shooters, Helios is going to be absolutely overkill, especially for gaming.

Rating: 9/10 (Detail Retrieval), 8.5 (Dynamics and speed), 8/10 (Timbre), 9/10 (imaging), 9/10 (Soundstage), 9/10 (Separation and transparency)

Source Pairing:​

Helios is harder to drive than usual. Listening experience will vary greatly depending on the source you are going to pair it with. It sounded the best with Sony WM1ZM2 among all the sources I have tried. But 1ZM2 is a $3600 DAP and I do not think many will run a $1100 IEM from a $3600 ToTL DAP. I would suggest doing trial and error runs with different sources and find out which one works best for you.



Helios is a prime example of how to make a good neutral IEM with solid tuning and technical prowess. If you are someone with a ~$1000 budget looking for utmost clarity and detail with above average soundstage and imaging, then Helios is easily one of the most compelling options out there, if not the best.
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d m41n man
d m41n man
Uhm.. wouldn't want to be the one to notice but in your photos, you have the IEMs connected in reverse polarity.
Sharp eyes! Yes. I corrected them later though while cable rolling.


100+ Head-Fier
Perfect treble at a major cost
Pros: Treble presentation
Above average staging
Top notch detail retrieval
Beautiful Bass Texture
Cons: Fit fit fit fit fit fit fit
Mids can be super dry and uninviting
Lower mids, mid bass and bass can be a bit too lean
Can be very hard to drive (Pro or a con)
I’m not sure why, but I have been putting off this review for a really long time. I have had the Helios now for about 4 months. I would say without much hesitation that this is a feat of audio engineering. With that said, this is 100% not a 5 star IEM. It has faults that make it an IEM I avoid for a few reasons.

graph (75).png

First thing first, I want to go on a fun side journey. For an IEM, Helios is pretty tough to drive. It sounds fine off most of the dongles I used but I had way more fun running it off of my tube amp or high gain on my RS6. I would call this scalability. The staging, the texture and the overall tone of the IEM changed with the sources I was able to use. The magic of using it on my RS6 or my tube amp really makes this feel like a desktop experience. Helios gets bonus points, because it’s not something I look for in IEMs, but was super fun to try.

I tested it with my Q5k, Hiby RS6, Questyle M15, Apple Dongle and Inspire IHA1 tube amp. The RS6 presents a very warm and tubey tonality, similar to my tube amp, while the M15 is more v shaped and punchy. I was able to pick up varying tonality with source switching. If this is appealing to you, Subtonic Storm and Symphonium Helios have to be the 2 IEMs on your list. It is something very unique and fun. Most importantly, Symphonium FLAT tech assures that other sources will not heavily alter the frequency response. I measured this and found it to be pretty much on point. 64audio also has LID, which is similar, but I had to alter the preamp to make sure I didn’t blow my ears out. Helios is legitimately hard to drive.

Fit and Ergonomics- This is well documented, but the fit sucks. I bought the IE900 for the fit knowing full well the tuning wasn’t for me; Helios was the opposite. I was so intrigued by the presentation and technical prowess that I had to get my hands on it. The shell is big, the nozzles are super long and the treble presentation gets better with a deeper fit. Getting a deep fit here is not particularly enjoyable. I can listen for about 1-3 hours before having to take a break. It also happens to be heavy with the cable sticking up in an interesting position. I think this creates the biggest flaw. The shell weight is towards the outer half of the IEM, while the nozzle holding it in place is fitting deep. This means that the weight is like a see saw only being supported by the canal. This is just a terrible fitting IEM. To note, Symphonium worked really hard on this and the Meteor is a fantastic fit IEM. 3/10


Bass- I found the bass on this IEM a little disappointing. If you have read my other reviews, you would know that my favorite bass is more in the warmth regions which is 200-400hz. Sub bass is nice as it can add to kick drums, but the sub bass meta of IEMs just doesn’t do much for me.
With this said, BA bass be damned. This IEM is both textured and slammy. On songs like How You Like That, the sub bass rattles the head a little and can actually be boosted for more slam. The texture in the sub region is also excellent. Usually, I struggle with sub bass, but this is just too good. The dip starts too early though and leaves the bass to mid bass regions very limp if not dead. It almost makes the IEM feel disjointed. There’s sub bass and then mids, but it feels like something is missing in the middle. This can be fixed very easily with EQ, however, most people don’t wanna deal with that. Due to the quality of the bass present, I will go 7/10. A bit of EQ can bring it a long way, but ultimately isn’t enough bass for a bass head and doesn’t reach far enough for someone who likes lower frequency strings like cellos and bass guitars.

Mids- I don’t really know how else to describe it, but the mids feel very... dry? They seem lifeless and without any sort of lusciousness. This is a clinic on imaging and presentation, but seems to have lost something in the middle. Jerry’s vocals on Cumberland Blues feel sad in a way; Dave Matthews vocals also have the same presentation. For what I listen to, the mids on the Helios are not really a strength. Comparing that to something like my A12t, which feels vibrant and textured, I don’t think the Helios really can compare in that regard. 4/10

Treble- Now this is where things get interesting. Since I have been in this hobby, treble has been a failing point of IEMs. Treble is a double edged sword. It requires finesse to help reveal the air and details in high percussion, flutes and violins. Most IEMs just get too hot *cough IE900 and IE600*, while others forget that treble exists. It seems like most IEMs have given up on treble, but Symphonium nailed something here. The treble extends well along a knife’s edge to the very last octave. High percussion and rides on Marcus Miller’s “Trip Trap” are presented like a perfect accompaniment to his fat bass riffs. Carter Beaford’s opening riffs on #41 are crisp. 99% of the time I find it unlistenable (whoever mixed that album was a treble masochist), but this treble is effortless. It reminds me of my Genelec 8030cs. A perfect balance of detail without pain and air without soaring too high. This is a 10/10 treble IEM and it leads to the next section of what makes it a special piece I have held onto.

Imaging- The IEM world has stepped up its game in imaging over the past few years. My go to IEM for detail and imaging was the JVC FDX1 for so many years. While also having major fit issues, it was also a bit spicy. It was well balanced and brought out details that are often never heard. After a while, I upgraded to the UERR and finally the A12t. These all have stellar imaging, but I would personally put Helios at the top. On orchestral pieces, you can hear pages turning, breathing, things dropping or even the audience coughing. In jazz recordings, you can hear the mannerisms of the player. Keith Jarrett’s moaning on live records or Miles Davis leading on Live - Evil. This is on par with A12t, Gaea, U12t and many of the other high detailed IEMs that are TOTL right now. The big difference is price. Helios’ used price is roughly $800 and new only $1200 placing it right in line with the big boys or even cheaper. If you want detail, like ALL OF THE DETAIL, the Helios is the IEM you want. 10/10

Staging- I would call it above average in stage width and height, but not the most mind blowing thing I have ever heard. It has a very clear right and left image with a well balanced center that projects outwards only slightly more than Meteor. If I had to compare, the Meteor is like a campfire with your best friends, while Helios is more like a larger concert hall and the Mest Mkii is like an Arena. Through most of my listening the widest and largest stage goes to the Mest Mkii or the A12t and I think that still holds true. 8/10

TLDR- This IEM is detailed, it’s neutral, it’s a bit on the dry and clinical side with a touch of sub bass and most of all it’s doing something no one else is really doing. It’s walking that fine line of air and sibilance with knife point accuracy. If, staging, imaging and detail are the only thing that matter to you, Helios is bar none the IEM to buy sub $1500.

For some comparisons

If you like staging more than anything, A12t and Mest Mkii are probably better values
If you like bass, texture and a more natural timbre, Meteor, IE900 (EQed) and A12t are better
If you like a super neutral detail monster with perfect treble, Helios is the answer
If you have tons of sources and like to try them Helios is the answer
If I could only pick one it would be Symphonium Meteor
So not only it wants to fit as deep as Etymotic, it’s girthy as well. Sounds like a nightmare. Do you have to sacrifice a lot of resolution going with Meteor instead of Helios?
@o0genesis0o Honestly, I think it's Helios has a ton more resolution. The Meteor is an amazing IEM, especially for lounging, but in terms of detail retrieval it doesn't come as close to the TOTL end as I'd like. I find the sacrifice for fit and tuning make it a better and more enjoyable experience, but if for sheer resolution, Helios is miles better.
Thanks! Very helpful. I can safely cross the Meteor off my wishlist now.


New Head-Fier
Detailed, Bright, Magical
Pros: Fantastic tuning and tonality
Great detail retrieval, imaging and separation
Scales very well with sources and volume
Coherency across the spectrum
Premium accessories (stock cable and case)
Cons: Fit due to the nozzle size and length
Might be a bit lean sounding for some listeners at first listen

A little background on myself and my audio preferences. I listen to IEMs throughout my workday so I generally get to put a lot of hours into listening to IEMs. I have been very fortunate to have had the opportunity to listen to a number of IEMs. Generally speaking, I enjoy a well balanced sound overall and I appreciate bass quality over quantity with slight forward-mids and a touch of brightness (less warm). Like the seasons, I cycle through a number of genres though my current library is a bit more mid/vocal-centric including but not limited to electronic, pop, rock, acoustic, etc. The following are my impressions which I hope can convey my feelings and thoughts when listening to a set of IEMs. I leave the reviewing to professionals who are much better at doing reviews :)

I was able to get about 80-100 hours on Helios with the mixed listening on the HiBy RS6 and the Qudelix 5k using the stock medium red/black silicone tips.

Helios, named after the Greek god of the sun and sight, immerses you in the music with a breath of fresh air that caresses your skin on a beautiful sunny day while you’re enjoying a leisurely stroll through the rolling green hills.



The bass is very well executed with an elevated sub bass shelf that does not bleed into the mids. While the bass isn’t the most impactful/punchy, it is far from lacking and can slam when called upon. The bass instead focuses on immersing you with detail and texture which is quite addicting with satisfactory impact. I love how the bass is layered with rich texture and details. I prefer bass quality over bass quantity and this minimizes any fatigue with my long listening sessions. I am very impressed that all of this bass is handled by a single balanced armature.

The mids are also quite polished with both female and male vocals coming in clean and crisp. There is a touch of brightness that works incredibly well for female vocals for both Western and Eastern genres. Helios is perhaps one of my favourite sets for listening to Lauren Mayberry from CHVRCHES with the other set being the Shuoer EJ07M. The touch of brightness doesn’t detract from male vocals too much and allows complex male vocals like Andrea Bocelli to shine through. On the other hand, I can see the mids being a touch lean, in particular, male vocals for some listeners though I find that to be a personal preference for most.

I was a little worried about the treble region at first since Helios’ treble is best enjoyed with deep insertion. Unfortunately, I couldn’t get a deep insertion but I was able to find a solid seal with a shallower fit using the stock tips. The treble region complements the bass and mids in a harmonic fashion. The treble region is presented with a sense of realism that comes across organic and feels like you’re in the room with the musicians. It sounds natural without any sense of being artificially boosted and that’s a winner in that region for me.


Engagement, Tonality, Source Pairing, Fit

The overall tonality is quite delightful and the balanced sound allows Helios to scale incredibly with various sources as well as cranking up the volume (for short durations). The symphonic tonality on Helios hits my preferences very well and can be enjoyed for long listening periods without fatigue. In some aspects, it reminds me of the MiM Dark Magician (OG) taken to the next level. The resolution in terms of detail retrieval, imaging, and separation are excellent and are among some of the best that I’ve heard to date.

In terms of source pairing with what I have on hand, Helios sounds great on both the Qudelix 5K (more neutral) and the HiBy RS6, which gives Helios a touch of warmth/colouration and is my favourite pairing between the two. Helios requires a bit more power and volume compared to other IEMs that I have tried in the past on both the Qudelix 5K and the RS6 though it can be easily driven on both.

Helios’ fit is the weakest point for me since I have smaller ear canals as the long and wide-ish nozzles prevent me from getting a deep insertion. It reminds me of my struggles with getting a good fit with the Sony IER-Z1R. This isn’t a problem for me though I can see some users preferring a warmer signature than Helios and I think Triton, the latest Symphonium IEM may be a better match for them.


Closing Thoughts

I went into listening to Helios without much background information or expectations since I tend to find it more fun and enjoyable that way. Had someone told me this was a tribrid, I would probably have believed them. Had someone told me only had 4 balanced armatures, I would have been quite skeptical having listened to the Dunu SA6, SoftEars RSV, and ThieAudio V16 among others; this isn’t a knock against any of those, it just shows how much thought and care went into the for tuning Helios. Helios sits among the top 3 of my neutral with a healthy sub bass boost IEMs and it would probably be my recommendation at the 1K+/- mark for those looking for this type of sound signature, the other being the Monarch MKII for it’s smooth and rich mids. If the fit was better for me, Helios would be an instant buy though it might have a chance of being added to my arsenal in the future. That being said, I enjoyed Helios thoroughly and I am looking forward to what Subtonic brings with their upcoming flagship IEM, Storm. I’m also excited to see what Subtonic and Symphonium will bring to us in the future. Helios is a prime example which illustrates what incredible tuning can do and embodies the phrase, quality over quantity.

Lastly, I want to give a shoutout to Leneo from Subtonic, and Felix from Symphonium for including me in the tour for Helios.


Headphoneus Supremus
Master of detail and clarity!
Pros: Highest 20kHz frequency response ever measured.
Very low overall harmonic distortion.
Close to flat impedance curve.
Spring-loaded 0.78mm 2-Pin socket.
Cons: Relatively large shell size and nozzle diameter (5.74mm) may not be suitable for those with a smaller ear canal.
01 P1430566a.jpg

02 P1430465.jpg 03 P1430643a.jpg 04 P1430657b.jpg

Conceptualized in early 2015, Symphonium has started to enter the high-end IEM market with their flagship IEM, the Helios. A 4-Way multi-driver balanced armature IEM.
MSRP: $1,099

Symphonium provided this IEM to me as a review sample in exchange for an honest and unbiased review. The company is not involved in any measurement process and editorial content of this review.

Notes: On the last 2 pictures above, the Left and Right connectors were reversed. I was taking pictures of the IEM drivers without cable then wrongly connected the Left and Right connectors to the drivers when taking the above pictures.

Durability, impedance linearity, and extended frequency response seem to be some of the important features of Helios. The shell is made of artificially tempered AL6061 Aluminium alloy to improve strength and hardness. And it is among few IEM models that utilize spring-loaded 0.78mm 2-Pin socket for maximum durability and consistent electrical contact even with frequent cable replacement. This is good news for cable aficionados because they can do cable replacement as often as they like on Helios without causing the 2-Pin socket to get loose. I swapped the cable many times between the stock 2.5mm cable and my 3.5mm cable and the grip of the 2-Pin socket is still consistent till now.

A common problem with multi-driver IEM is impedance linearity. It is often that the non-linear impedance curve of a multi-driver IEM causes tonality shift when connected to headphone output with relatively high output impedance. Helios is designed with a close to flat impedance curve for consistent tonality across multiple devices. This is a rare feature for a 4-way multi-driver IEM.

I measured Helios several times to check the consistency of my measurement and keep seeing that 20kHz frequency response sticks out like no other IEMs I’ve ever measured before. And the clean extended sub-bass response is quite impressive from a fully balanced armature IEM. Helios is a kilo-buck IEM and it seems to deliver what is expected from a kilo-buck IEM.


Highest 20kHz frequency response ever measured.
Very low overall harmonic distortion.
Close to flat impedance curve.
Spring-loaded 0.78mm 2-Pin socket.


Relatively large shell size and nozzle diameter (5.74mm) may not be suitable for those with a smaller ear canal.


To improve shell shape and size for better fit and comfort. The shell is a bit too large and protruding out from the ear. And to slightly reduce the nozzle diameter for better fitting.

The following is my guideline for the sound & engineering quality rating criteria that will be used in this review:
M00 Earfonia Rating Criteria.png

Sound Quality​

Frequency response is compared to Earfonia IEM Target Curve (EITC-2021):
M00 EITC-2021 v2 - 1920px.png

*More info about EITC-2021 here.

Symphonium Helios measured frequency response normalized at 94 dB SPL @ 500Hz:
M01 EITC-2021 - Symphonium Helios normalized at 94 dBSPL at 500Hz.png

Symphonium Helios measured frequency response normalized at the midrange dip:
M02 EITC-2021 - Symphonium Helios normalized at Midrange Dip.png

Symphonium Helios measured frequency response in comparison to Harman Target IE 2019:
M03 Harman Target 2019 - Symphonium Helios.png

The following is frequency analysis based on the 4 observation points on EITC-2021:
M04 Slide1.PNG

Overall Sound Signature:​

Mild V-shape tonality with clarity-oriented tuning. Excellent sub-bass and upper treble extensions.

From the frequency response graph, we can observe the followings:
  • Helios frequency response is within ±3 dB from my EITC-2021 observations points.
  • Helios frequency response around the bass and midrange area is within ±3 dB from the Harman Target IE 2019.
  • The midrange peak (Mp) and 1st treble peak (T1p) are pretty close to my preferred target.
  • The mid-bass to low-mid area is a bit recessed.
  • Besides the T1p at around 4.26kHz, there is another treble peak close to it at around 5.57kHz. Since T2p is the expected resonance peak, I call this 5.57kHz peak the 3rd treble peak or T3p. I’ve seen this T3p on other IEM like the Fiio FH7. From what I’ve observed, the effect of T3p seems to enhance the perceived clarity.
  • So far, I’ve never seen a 20kHz measured response as high as the Helios. A very interesting phenomenon. I measured several times to check consistency and the results are consistent. Helios is the only IEM that I’ve ever measured with this kind of ‘real' 20kHz upper treble extension. Remarkable! It also shows that my measurement setup can measure up to 20kHz.

Squeaky clean or shiny clean is the first thing that came into my mind when listening to Symphonium Audio Helios. It's slightly bright tuning with properly boosted sub-bass creates a unique mild V-shape tuning that is borderline analytical. Tonality is still quite balanced, and I won’t call it a bright-analytical sounding IEM, but there is an analytical nature in the sound signature. Records sound clean and detailed, while still maintaining a relatively balanced tonality.

The lower midrange sounds a tad recessed and the midrange body sounds a bit lean on vocal. I prefer a slightly fuller and warmer midrange. I guess Helios is not meant for those who are looking for warm and lush-sounding mids, instead, detail and clarity are the main themes here. The midrange probably can be described as 'neutralish' clean-sounding midrange with a high level of perceived detail and clarity. When listening to female vocals sometimes I hear some emphasis on the breathing sound a bit more than what I used to hear from my other favorite IEMs. Helios sounds ok with vocals but may not be my first choice of IEM for vocals as I prefer a fuller-sounding vocal. Instead, I think it is among the best IEM for instrumental and orchestral works.

Bass is tuned to emphasize more on the sub-bass, likely to avoid bass bloat that often spoils the mids. There is no bloated or boomy bass here, bass sounds super tight and deep. And the bass can be quite thunderous when the music calls for it. The mid-bass punch is good, but I prefer a tad more mid-bass body to improve the overall balance between sub-bass and mid-bass.

Treble is the pinnacle of Helios tonality, as the overall tonality is slightly emphasized in the treble area. The treble sounds very smooth with probably the best upper treble extension that I've ever heard. Helios treble tuning is executed brilliantly. I have no problem with sibilance even when listening to a rather bright vocal recording. There is no sharp or peaky shrill treble but flaws in the bad recording will be revealed without mercy. The treble tuning makes the Helios shines.

Perceived detail and clarity are the most prominent aspects of the sound signature. Helios is a master of perceived detail and clarity. Another quality that impressed me is the instrument separation and positioning that are presented with surgical precision. I’m a fan of David Garrett but I often don’t get the level of instrument separation that I would like to hear from his recordings. Helios solves this issue, and it has been my first choice of IEM for listening to David Garrett's albums and other similar orchestral works. Transient and attack are lightning-fast while the boosted sub-bass adds power and liveliness to the dynamic. Helios is a lively sounding IEM, not by boosting the bass as many IEMs do, but by presenting music with lifelike detail and clarity.

Comparisons to FitEar To Go! 334 & Fiio FH7​

05 P1430615a.jpg

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M05 Symphonium Helios - FitEar To Go 334.png

FitEar made its debut around a decade ago and I was a fan of the ‘To Go! 334’ smooth warm and pleasing sound signature. In the last few years, I have done quite a lot of audio recording and mixing work, and that changed my personal preference for sound quality. My requirement for perceived detail and clarity increases because those qualities help me to hear more detail during recording and mixing. Now I feel FitEar To Go! 334 sounds a bit too warm. Helios sound more neutral and has higher perceived detail and clarity with better instrument separation than the To Go! 334. I would choose Helios over To Go! 334 any time of the day.

M06 Symphonium Helios - Fiio FH7 w Green Filter.png

Fiio FH7 has 3 tuning filters: Green, Black, and Red. The Green filter is just a mesh without any filter, while the Black and Red filters dampen the treble in different degrees. Most of the time I use the Green filter as it sounds the most transparent to me. The FH7 with the Green filter sounds a bit more balance and less V-shape than Helios. The midrange sounds fuller and nicer on vocals. From the tonality perspective, I would say FH7 tuning is the better all-rounder than Helios by a small margin, while Helios still has the edge for perceived detail, clarity, and instrument separation. Helios also sounds a bit dryer compared to FH7. Both are nice IEMs and although they have a different sound signature, in my book sound quality wise they are in the same league. I would take the FH7 for vocal and Helios for instrumental and orchestral works. But on other technical aspects like Left-Right mismatch, distortion, and impedance linearity, Helios wins.

Equalization to Match EITC-2021​

One of the objectives of my EITC-2021 target curve is that it is a ‘realistically achievable target curve’ by my measurement equipment. It is based on real measurements and not just an estimated target curve. To test and experience an IEM with matching frequency response to EITC-2021 sounds like, I created an equalizer profile for Symphonium Helios to match EITC-2021.

Symphonium Helios frequency response (Red curve) after equalization to match EITC-2021 target curve (Blue curve):
M07 Symphonium Helios - equalized to match EITC-2021.png

To me, EITC-2021 equalization improves Helios' tonal balance. The midrange sounds more natural. I use REW to create the equalizer profile based on the difference between Helios' average response and EITC-2021. Then exported the equalizer profile as a text file to be loaded to Equalizer APO.

Below is the download link for the equalizer profile for Symphonium Helios to match the EITC-2021, so anyone who would like to try EITC-2021 on their Symphonium Helios can load it to Equalizer APO to test it. Please apply a -3dB gain to avoid clipping.
Symphonium Helios to EITC-2021 EQ APO v1.3

Engineering Quality​

M09 Engineering Quaity.PNG

Disclaimer: The measurement results of the engineering quality measurement in this review represent only the pair of IEM that was measured for this review. It doesn’t represent the overall quality control of the factory.

Left-Right Match​

Observation range: 20Hz – 7kHz
The review sample of Helios shows excellent left and right channel tracking. My unit has an overall 0.5dB matching from 20Hz-5kHz, with only 1.2dB maximum at around 5.4kHz.

M10 Symphonium Helios - Left-Right Channel Mismatch.png

Harmonic Distortion​

Observation range: 55Hz – 7.1kHz
Overall THD level of the Symphonium Helios is quite low even at the peak. Left and Right channels show similar THD profiles. There is no abnormal distortion peak across the measurement range. Please take note that distortion measurement is not part of sound quality evaluation. It is only used to observe the engineering quality of the IEM.

Distortion measurement at 94 dB SPL at 500Hz:
M11 Symphonium Helios - Left - THD at 94dB.png

M12 Symphonium Helios - Right - THD at 94dB.png

Distortion measurement at 104 dB SPL at 500Hz:
M13 Symphonium Helios - Left - THD at 104dB.png

M14 Symphonium Helios - Right - THD at 104dB.png

An interesting observation of the harmonic distortion profile, in general, the odd harmonics are higher than the even harmonics. Probably that’s what gives the analytical nature to the sound signature of Helios. But since the overall distortion level is quite low, I don’t consider it a concern.
M15 Symphonium Helios - Right - 104dB Distortion - 2nd-5th Harmonics.png

Electrical Impedance​

Observation range: 20Hz – 20kHz
The impedance curve is almost ruler flat, with only a gentle roll-off after 13kHz. I’ve never measured a multi-driver BA IEM with impedance as linear as Helios before. This is an engineering quality that deserves acknowledgment. The following is the impedance curve of the Left and Right channels of Helios, Fiio FH7, and FitEar To Go! 334 for comparison.
M16 Impedance Symphonium Helios - Fiio FH7 - FitEar To Go 334 v2.png


At 92.9 dBA SPL at 100mV @ 1kHz Helios’ sensitivity is quite low, lower than the Etymotic ER2XR which is already quite low. But my old mobile phone, Samsung Galaxy S9+, still can drive Helios to a sufficient loudness level. So, in most setups, it is not a concern. Most portable devices would be able to drive Helios sufficiently, but a good quality DAC+Amp will improve the perceived dynamic, liveliness, and overall sound quality. I suspect the low sensitivity could be due to a resistor network inside the IEM that is used to flatten the impedance curve.

Fit, Comfort, & Build Quality​

Besides the regular Silicone ear tips, Helios comes with ‘Azla SednaEarfit’ ear tips which feel more rubbery than regular Silicone ear tips. To me, the ‘Azla SednaEarfit’ gives slightly better comfort and grip.

The shell nozzle is lipless, but I don’t have a problem with ear tips sliding off the nozzle. Probably the large nozzle diameter and the matte finish of the surface help to grip the ear tips quite well. With around 5.74mm nozzle diameter, I would advise those with smaller ear canals to consider testing the fitting before buying Helios. I always use medium-size ear tips with other IEMs, but with Helios and ‘Azla SednaEarfit’ ear tips I use the small size ear tip for better fitting. Fitting could be an issue for those who usually use small size ear tips.

Helios' shell size is rather large. In my opinion, the shell thickness is rather too thick that it tends to protrude out of the ear. And I would suggest the part shown in the 2nd picture below be curved in for a better fitting. I asked Symphonium Audio why the shell size is that large, and they said it is due to the high-quality components that they use requiring more space inside the shell.

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I have used Helios for long listening sessions as well as mixing my recordings. I consider the fit and comfort are ok but not great. Subjectively I would rate the comfort level as 7/10. Aesthetically I’m not a fan of large and thick shells, and I hope Symphonium could come up with a better shell design for their future IEMs.

Left and Right indicators are on the cable connectors. To connect the driver with the correct polarity, the groove of the connector is to face the outer side of the shell.

Build quality of Helios is generally very good. The shell feels very solid and durable. I’ve used them for about 2 months without extra care, and I don’t see any scratches on the shell surface. It seems that it is built to last.

Metal Shell to Ground Pin Connection: Not connected​


Suitable for critical listening and Pro Audio applications, and any other applications where a high level of perceived detail and clarity, wide frequency extension, and linear impedance curve are important.

Kudos to Symphonium Audio, the Helios achieved ALL GREEN on all my quality ratings!

More information about my IEM Measurement Setup & Methodology:
Earfonia IEM Measurement Setup & Methodology

Advertised Technical Specifications:​

Driver Crossover: Custom Tuned True 4-Way Crossover with FLAT Technology
Frequency Response: 12Hz - 24kHz, ± 2 dB
Sensitivity: 104dB/Vrms @ 1 kHz
Impedance: 8.5 Ohms @ 1 kHz
Socket: Spring Loaded 0.78mm 2-Pin
Cable: 26 AWG Pure OCC Copper
Cable Impedance: 0.20 Ohms (2.5mm), 0.25 Ohms (3.5mm), 0.28 Ohms (4.4mm) @ 1kHz
Warranty: Limited 1 - Year Warranty
Amazing review! Did you happen to check distortion after EQ? Wondering how much bass EQ those BA's can take and still perform.
Tx! I didn't measure the distortion after EQ. Because to measure the FR with EQ I have to switch the audio driver from ASIO to Java driver. And with Java driver the distortion is always higher. So not apple to apple comparison. But to my ears the EQ doesn't seem to introduce any audible distortion at all.
Thank you for indicating the nozzle width :thumbsup:


1000+ Head-Fier
Voodoo Magic
Pros: Great bass for a BA. Wonderful tuning all round. Neat soundstage and imaging.
Cons: Fitment dues to huge shells.

I have always been a fan of hybrids vs all BA IEMs for the longest time now. I heard lots of love towards a new all BA IEM called the Helios and I wanted to see what all the hype was about. Symphonium is a new name to me and the Helios which is their flagship IEM, is the first product I’ve had a chance to check out from them. This is also a product that was a collaboration with another company called Subtonic. I was lucky enough to last minute jump on a demo tour for the Helios. The Helios is using a 4 balanced armature setup in a fully sealed housing.

Quick shoutout to Symphonium for sending the Helios to test and review. While I always appreciate the chance to test and review products sent in from manufacturers, it never affects the rating of my reviews.

The Helios can be picked up from Symphonium’s website below.

Onto the review of the Symphonium Helios! My personal preference is a hybrid/tribrid IEM where I get good hitting bass and have a detailed treble with decent mids. When it comes to an over ear headphone I prefer a spacious sound with a deep low end, the mids to be more forward and the highs to be a little bright with some sparkle. I listen to a lot of genres but I hover in the classic rock, blues and edm music with some rap here and there.

Gear Used​

IPhone 12 pro with headphone adapter, iFi Go Blu, Weiss DAC and SMSL SU-9 feeding the SP400 amp.

Looks and fit​

This has to be the most boring looking IEM I’ve seen in a while. It’s a nice metal shell that has a nice black texture to it. It feels like a really good quality item but it just looks simple. The shell is absolutely huge compared to anything I have at the moment. It almost looks excessive but I was told it was to fit all the extra components and to help with tuning. Which I definitely believe after listening to them.


Since this is an all BA design, Isolation is fantastic. Passive isolation is wonderful and others can’t easily hear what I’m listening to. This would be a fantastic IEM to take on flights, noisy environments, ect..

Packaging and accessories​

We get a nice average sized box with the case and IEMs sitting on top. On the front side of the box is a little shelf which holds the ear tips and metal card which holds the serial number. I think the included accessories are perfectly fine, though I don’t like the case as much since the threads can squeak when undoing the case. Not the end of the world but something to note. I totally woke up my fiancé with the case noise at least a few times at night.


These final impressions were done off a mix of the iFi GO blu and the SMSL SU-9 connected to the SMSL SP400. These are what the Helios sounded like to my ears. This was also using the stock wide bore eartips. Things like ear tip selection and DAC/amp selection will produce different results and impressions vs what my ears hear on my specific gear.

My title for this says voodoo magic and that’s exactly what this tuning is. The bass is fantastic for a BA setup. On first listen I was confused and checked the website to make sure this wasn’t a hybrid. It does well in terms of extension and manages to still rumble with wonderful impact. This is something I don’t think I’ve experienced before with any BA IEM. The mids are super clear and I rather enjoyed the instruments and vocals I got from the Helios. Nothing was ever harsh but I still got really good details from the vocals and mids overall. The treble was fairly good as well. A little bright at times with the tips I used but it pulled fairly good details up top. Not quite the best I’ve heard but it's really good for the price the Helios comes in at. Everything has a nice sparkle with just the right amount of splash. I was overly excited almost every time I listened to Helios. This is a wonderful tuning.


The Helios doesn’t have a super wide tuning but it does have a really weird depth. I’m used to a deep depth but the Helios has a weird depth that isn't super deep yet it managed to have a little backwards depth. It’s hard to explain but it almost gives a 3D effect. It’s not super crazy but there were a few times I experienced it and was fairly surprised/impressed. I’ve yet to experience that other than a few full sized headphones. Imaging is really good here and it was easy for me to pick out things on the stage when listening. Once again there is some voodoo magic going on with the Helios.

Stock cable​

I didn’t cable roll this time since the Helios is so big. I did try a few cables but the ear guides they all had made the fitment weird or uncomfortable. The stock cable doesn’t have a traditional ear guide since it sticks out so far. Luckily I liked the stock cable and its a really nice quality braid and the hardware accents are all really nice quality. I wouldn’t change the setup at all unless you want to play around with different cable material. Just keep note that these would do better with non ear guide cables.

Tip rolling​

I did try trip rolling a little to see what tips I liked the most. The Spinfit tips are usually my go to for 90% of my IEMs but they all added just a bit too much sibilance to the helios for my tastes. The stock small bore tips were good but they felt like the stage wasn't as wide and the treble felt a little too tame at times for my taste. The stock wide bore tips are what I ended up really liking and it did calm the harder sub bass hits I got with the small bore tips, but the treble opened up more and had an airiness that I really liked. Tips rolling will always be subjective but it can make a big difference so I would definitely say tip roll to see what you might like with the Helios.

IEM comparisons​

Moondrop S8​

The S8 is also an all BA design coming in a few hundred less than the Helios. The big difference between the two is definitely the effort put into the tuning. The S8 has a more lean sound compared to the Helios. The lows were pretty good to me for a BA IEM when I first heard the S8 but it was always lacking any real impact. This isn’t the case with the Helios. The mids and treble have a more intense presentation on the S8 but I get a better balance and more detail out of the Helios. The Helios is definitely a step up in my eyes over the S8. You can tell the team that did the tuning of the Helios really put some listening time on them as the S8 sounds a little lacking with its sometimes(to me) hollow sound.

Kinera Nanna Pro​

The Nanna is still fresh to me but I really like the clarity and details I get out of the mids and throughout the treble. The lows are much better on the Helios but the Helios is really good at being an “all rounder” to my ears. The Nanna is very detailed when it comes to vocals and the lower-mid treble. This set is really nice with certain genres but not so much for a daily IEM that works well with everything I listen too. I can’t really say which is better. I think the detail retrieval goes to the Nanna but the Helios does the lows better and the staging is much wider and deeper on the Helios vs the Nanna. Go with the Nanna if you listen to mostly rock, anything with vocals and music with a big focus on instruments. Or if you have the money to have multiple expensive(to me) IEMs. I you want one thing only then the Helios might be the better option for an "all rounder".

THIEAUDIO Clairvoyance​

THIEAUDIO’s Clairvoyance is my favorite IEM still. I find that the Helios is a step above the Clairs in terms of detail retrieval. The mids and treble do sound a little better on the Helios as well. That being said, the Clairs are a smaller shell and I find them more comfortable. The Helios is huge and I find myself adjusting the fit a little more if I’m moving around. The Clairs still have a special magic about them and even though I really like the Helios, I find myself still reaching for my Clairs. This could be a simple bias due to these having some of my favorite tuning in recent times. The Helios also has a better stock cable and where I instantly replaced the stock Clair cable, I would absolutely keep the Helios stock cable.

Amping Combinations​

iFi GO Blu​

The GO blu is my current favorite portable and it does the Helios justice. The little DAC/amp is able to bring enough power to give the helios a nice detailed bass and subbass, keep the mids warm with decent detail retrieval and the top end frequencies sound fairly clear with good details coming in. Staging isn’t quite as wide as some of the desktop gear I tested with but I still really liked this pairing and It’s usually what I use the Helios with around the house or at night before sleeping.

SMSL SU-9/SP400​

Scaling seems to be a thing with the Helios and I was able to squeeze a little more of everything moving from the portable stuff like the iFi GO blu/hip dac to a desktop stack. The SMSL stack was able to bring out a little deeper and impactful lows. The mids stayed warmer yet clear and the treble seemed to brighten just a little bit more. Detail retrieval off the desktop stack was definitely better than the portable gear but I don’t think the Helios needs to be tethered to a desk and can be enjoyed just fine off portable gear if used on the go. I did notice the Helios does seem to like power and this is probably the most power hungry IEM I've used on my SP400.

Weiss DAC​

The Weiss DAC is wonderful in terms of detail clarity and retrieval. It has brought out some faults in other IEMs that I thought weren't bad until plugging them into the Weiss DAC. The Helios sounded on a whole different level when I listened to it on the Weiss DAC. The lows felt super detailed and each sub bass hit felt more vivid. The mids ended up staying around the same but vocals really popped and felt more realistic. Treble really came alive and it felt like everything had just a bit more energy and clarity that made a huge difference to my listening experience. The staging was wider and deeper both front to back, resulting in a feeling of being in the center of a song versus in front of the band. All in all, the Helios can definitely scale higher than my go to SMSL desktop stack.

Overall thoughts​

The Helios is absolutely fantastic and I had an absolute blast with the set. I rarely get excited for stuff around the $1000 and above mark but there is just something about the Helios that just keeps bringing me back to them. I think these are a great IEM to have in anyone's inventory and I highly recommend them! They do some really interesting things with their tuning and whatever voodoo magic they did with the Helios, I’m hoping to see in future product releases. Good job to both the Symphonium and the Subtonic team and look forward to seeing what comes out next. Thanks for reading!
Ace Bee
Ace Bee
Nanna 2.0 pro uses a DD for lows. Does the Helios have an even more natural low end than DD lows?
The DD driver in the Nanna 2.0 isn't very prominent to my ears. It comes off lean to me when compared to the Helios. I just didn't find the DD in the Nana all that good. The Helios just doesn't sound like any BA I've heard to date. It sounds like a DD in terms of impact though which is strange.
John Massaria
John Massaria
the Nanna needs a proper high powered portable amp <---- true story.... they are power hungry and sound best with something like a Cayin C9 or the Dethenray Honey H1


100+ Head-Fier
Kilobuck Treble contender
Pros: One of the best treble responses I have ever heard
Clean bass line
Amazing details and resolution
Great timbre
Cons: The bass might be too clean, which shares both pro and cons of the ThieAudio Monarch
A bit boxy for vocal, that or it will be a bit recessed for female vocal
Average staging performance
Size is a bit too big, might be uncomfy for some ears

If don't know about Symphonium Audio or Subtonic by the time of this writing, then I don't blame you - until I got the tour unit I don't either. Though by chance if you know @toranku, then you might know a bit about Subtonic, though that's as far as I can say.

The Symphonium Helios is a collaboration IEM between Subtonic and Symphonium. If anything, this work also marks the first appearance of Subtonic in the market. Incidentally, with its pricing of ~1000$, both brands are showing their confidence in this collaboration by challenging the renowned top dog of the IEM chamber as well.

Will this be a triumph of the underdog or just a show-off like someone who all barks with no bites, let's find out.

This review is a copy from my blog, with some edit to fit the Head-fi review format
My listening preference and gear can be found here.


The Symphonium Helios unit was kindly provided by Symphonium in exchange for my honest review.

Build and Accessories:​


  • 3 pairs of AZLA SednaEarfit ear tips (S/M/L)
  • 3 pairs of silicone ear tips (S/M/L)
  • Balanced 2.5mm 2-pin 0.78mm cable
  • Brushes
  • The IEM itself
For an IEM that's over 1000$, the Helios packaging is quite simple.

Nothing much to say about the accessories except that the metal case is quite durable. It's solid, which might help if I want to get someone to the hospital if I try hard enough. My only complaint is that the lettering on the case does start to wear off during my usage. They surprisingly are just a bunch of stickers and not etched into the case.

Not that it ruins the quality of the case itself anyway, but on to a cosmetic point...
The Symphonium Helios fit itself is... odd. I am not that irritated by its shape as much as how there seems to be a pocket of air inside of my canal every time I wear it. Some other aspects of the nozzle design need to be considered as well, such as a long and wide nozzle. For people who are aware of the Blessing 2 design, imagine the Helios fit in a similar fashion. Admittedly it's not as wide, but you might want a deep fit on this set for sound quality reasons (which I will mention in the analysis).

Other than that, I cannot think of any other potential problem for the wearers. Maybe its triangular design can be irritating (It's a bit similar to the Tanchjim Oxygen or the Hana if you know about it), but that's about it. The black shell design of the Helios sure is charming on some fronts while being solid and durable too.

The included Sedna tips is nice to have, though for my ear it wasn't the most optimal (there was no SS size). For the sake of information, I have tested the Helios with:
- AZLA SednaEarfit - SS size (Yes, I bought this)
- Acoustune AET07 - S size
- Sony Hybrid - SS size
- Final E - SS size

The review will mainly based on the AZLA SednaEarfit and the Acoustune AET07


Standalone analysis:​

One look at the graph might consider the Helios to be Mild-V. While my impression partly agrees with this notion, the Helios, in my opinion, follows a Neutral with Sub-bass boost sound signature, though some might regard the Helios as neutral bright even.


The Symphonium Helios Frequency response can be seen from the Frequency Response Index

Yes, ~10dB of bass gain is a lot here, though if you pay attention to the bass shelf starting at 200Hz as well as look at how lean the bassline is, you will realize that the boost is relatively clean, too clean even.

That leads me to the first problem with the Helios, which is:

The Helios has the ThieAudio Monarch symdrome (somewhat).
In my ThieAudio Monarch review that was written a year ago, I had one remark about its bass performance:

Speaking of sub-bass, it's excellent and it is one of the reasons why I would recommend this IEM for sub-bass lovers due to how satisfying it is. That being said, while the 150Hz boost keeps the bassline clean from bleeding into the mid-range, I sometimes find myself wanting a bit more punch for some of my electronic tracks.

Let me remind you that as far as description goes, this is just a relative comparison. But the impression of the hefty mid-bass impact when listening to the Helios is what reminds me of this notion of the Monarch.

And again, this is not by any means a bad thing, and I would prefer a clean bassline to an overly bloated bass performance any day. But putting myself inside the shoes of a bass head?

Then you might as well look for other IEMs unless quality is what you are longing for more than quantity.
That said, the similarities with the Monarch end there. While the Monarch remains forward with some of the high-vocalists that I listened to (Nanahira, Natsume Itsuki...), the Helios does the opposite as these types of vocals tend to range from "neutral" to "recessed." Female vocalists who utilize lower ranges of frequencies like Nakae Mitsuki on the other hand, work well despite being a little bit boxy. It's due to the former trait of the Helios that I tend to crank the Helios volume up a bit for vocal songs that don't employ an overwhelming number of instruments, though that alone doesn't fix its problem when presenting bowed string instruments like cello or violin.

Its staging performance also isn't the best either. The Helios tends to lack some width and its imaging presentation resembles a "blob effect" sensation where you can only point out the difference between left, center, and right.

Or for anyone who knows the "flowery" term, the Helios isn't as diffuse in its stage performance as I would prefer.
Mind you, this effect is not as apparent as a lot of IEM out there, but that alone isn't enough for me to consider it above average anyway.

Out of those potentially problematic issues that I got with the Helios personally though, the Helios is simply terrific in some front that I would prefer it over some TOTLs, some of which include.

The Helios treble performance is among one of the best that I have experienced
This is the aspect that I love the most about this IEM; the Helios simply just sparkles without any sense of unevenness or weird "zing" that I experienced with other IEMs, like the 64 Audio U18s. It achieves all of this while remaining fast and sharp. And damn it is an understatement if I don't say that the Helios treble performance carries a lot here considering the number of IEMs that I enjoy purely because of their treble performance, like the Sony IER-Z1R, ThieAudio Monarch...

That said, knowing how I usually wear these IEMs, I have to bring out my disclaimer about how you should deep fit these IEMs as it tends to vary a lot between a person and tip choices. Otherwise, don't come back to me and complain how spikey the treble on the Helios is.

But overall, the Helios treble received no complaints; it works so well with some of my favorite Japanese/Chinese Oriental tracks, from instrumental to just plain Electronic EDM.

Next up,

The Helios detail retrieval is suprisingly terrific
Now, this isn't saying that the Helios has the best detail retrieval ability out there, but it's among one of the brightest contenders on my list. This with the clean tuning and treble performance makes the Helios the perfect detail and clarity machine as these qualities (imho) just amplify each other once executed perfectly. Some might consider the Helios being technical for this reason and I agree. But due to its tonal performance, it stays out of the "dry" criticism that I usually mention with IEMs like the Etymotic ER4S/SR/XR.

And this is not to mention it's coherency and timbre
Which is mostly an afterthought at this point considering what I have said above about the Helios. But it's worth mentioning anyway. Note that I consider coherency and timbre as two different things despite having small relations to each other. But for the Helios, it doesn't matter anyway as it keeps the whole sound spectrum streamlined without any serious common timbral quirks that I found in BA/Multi-BA sets.

Select Comparisons:​

vs Unique Melody MEST MKII:

Comparison graph was generated from the Graph Comparison Tool

In hindsight, the MEST MKI might be more forward and exciting, but I want to make the comparison with the MEST MKII as the contrast between these two sets is clearer.

First and foremost though, one can consider from this graph alone that the Helios is more forward and has more bass punch, and for some of the parts, you are not wrong. Though to correlate this with my actual listening experience, I would say that the MKII is the slightly bassier one mainly due to my listening habit of cranking the volume if I found the ear-gain is lacking. This means with my desirable listening level for each IEM respectively, I perceived more bass with the MEST MKII.

That said, even if I normalize both of these IEM to the same level, or crank the volume up, it doesn't change how I see both Symphonium Helios and Unique Melody MEST MKII as two IEMs that can be regarded as the same rank in performance but for different reasons.

Or in short, the Helios is the more exciting one while the MEST MKII is tamer one
Of course, I would pick the Helios over the MEST MKII, cranking volume can do so much. The Helios treble is just something I absolutely enjoy despite some might have problems with it. Take the MEST MKII if you want a warmer, relaxed tone.

vs Sony IER-Z1R:

Comparison graph was generated from the Graph Comparison Tool

t's not that often that I bring the IER-Z1R into the conversation. But then, it is one of my favorite IEMs to the point I personally own a unit because of that.

I have mentioned that the Symphonium Helios and the Sony IER-Z1R are among my favorites in terms of treble performance, but how exactly, and which would I exactly choose?

To be frank, it's difficult to answer. At most, I would consider treble in the same caliber despite showing different traits. What they do share though is an amazing transient performance that gives both IEMs sparkles without going overboard. While the Helios "zingy" trait in its treble presentation might be more addicting to some, the Z1R makes up for it with its sheer, upfront treble presentation, which keeps the song energetic.

Ultimately, I would still pick the IER-Z1R over the Helios. This is even with my bold claim that the Helios is more resolving than the IER-Z1R; it just kicks the bucket when Staging and Imaging performance is mentioned. The IER-Z1R has a grand, diffuse presentation in its stage while keeping the instrument deadly precise. And details? It is still one of the top dogs in the market, despite might falling short of some similarly priced IEMs.

Of course, it is not an IER-Z1R comparison without mentioning its bass performance, but is that a fair comparison at this point? Maybe some of you can argue the Z1R bass is a bit bloated, but I have personally never seen it like that.

Anyhow, while I do have preferences on what is worth the price, both are amazing IEMs respectively. Of course, the Helios might have an advantage here when it comes to price, but what do you say? These are two kilobuck IEMs after all.

vs Moondrop S8:

Symphonium Helios vs Moondrop S8- Comparison graph was generated from the Graph Comparison Tool

While both IEM are using a multi-BA setup, the Symphonium Helios just blows the Moondrop S8 out of the water for me thanks to its treble performance and its resolution.

Considering how I have been praising it, this doesn't need to explain much isn't it.
I would still consider the Moondrop S8 to be a relatively safe IEM (We don't talk about the Blessing 2 here), despite that the Harman-neutral signature of the S8 comes out as a little bit shouty when I am listening to vocal tracks. But the Helios weirdly is the more engaging IEM for me. Maybe it's because of the treble response that created all of this energy into the song, or the Helios has slightly more bass as well. Thanks to this, the Moondrop S8 just seems the tamer one, despite the forward upper-mid.

Staging/Imaging performance wise, I would consider both to be of the same caliber. As the S8 might have more accurate positioning, its stage doesn't have the depth and height as the Helios does. Though I reckon no one will care unless they are picky about positional cues.


Because I cannot miss an opportunity to mess with an IEM that has a treble response this good.
based on the Banbeucmas Preference Target:


Filter: Peaking; Frequency: 250Hz; Gain: +0.6dB; Q : 1.4
Filter: Peaking; Frequency: 700Hz; Gain: -3.3dB; Q : 0.9
Filter: Peaking; Frequency: 6500Hz; Gain: -2.4dB; Q : 1.3

Preamp gain: 0dB
The most obvious equalization that I will do and surprisingly it's quite easy to do also. Most of all in this equalization I don't need to employ any Preamp gain. My preference target has always been trying to be neutral while keeping the sound engaging, and Helios' treble response is perfect for that. The only thing that doesn't line up here is the sub-bass; it's there to keep the integrity of the Helios along with its sparkly treble.
What I am happy is with how minimal the EQ effort is needed for this to shine. This also allows me to keep my volume knob at a constant value without readjusting depending on the tracks as discussed in the analysis section.

Be warned: This does actually made the Helios sounds a bit thinner due to my taste but might irks some users since the Helios is already "thin".
I actually would prefer keeping the EQ up rather than the stock sound this time around. Quite a rare occasion considering every IEM that I use daily are with its stock sound (Except the Moondrop SSR).

Other equalization suggestion(s):


Filter: Peaking; Frequency: 100Hz; Gain: 4dB; Q : 0.3

Preamp gain: -4dB
This one is a bit simpler, with the whole intention of trying to make the Helios bassier. This does make vocal sounds more recessed for my ears, though the goal is achieved to some extent.


For an IEM that's at kilobuck price, the Helios sure doesn't disappoint. While it has its own flaws, it managed to nail a lot in my book while keeping itself as a decent contender in the market.
With EQ this is one of my favorite set that I use interchangbly with the IER-Z1R during my testing week.
But whether I am judging the Symphonium Helios with EQ or not (which I am not btw), it's an IEM that is priced right considering how the market goes.
Now, to the parents of this love child, I am looking forward to what you guys have in store, either separately or as a team.
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1000+ Head-Fier
Interferences at 1000
Pros: Excellent treble.
- Technical and analytical sound.
- Remarkable tuning.
- Bass is quite good for a BA driver.
- Good tuning.
- It's a nice touch that they have included the impedance of the cable.
- Robust construction.
Cons: Big problems when pairing them with most of my sources: noise, interference, clicks, etc.
- Very heavy metal case, which limits its use as a carry case.
- Fairly sized leather case.
- Limited accessories, despite the inclusion of Azla SednaEarfit tips.
- Simple design.
- The cable connection to the capsule is not well integrated.

According to its website: "Symphonium was conceptualised in early 2015" in Singapore. Its founding members did not agree with the current offer and decided to create their own IEMS. They currently have 3 models: the cheapest is called Mirage ($169), in the mid-range is the Aurora ($248) and the most expensive by far is the model I am currently reviewing, called Helios, priced at $1099. This is a pure four-driver multi BA, designed in collaboration with Subtonic. Built to last, it is constructed from the T6 variant of AL6061 aluminium alloy. It has a 4-way crossover, uses high-quality components from Panasonic and Vishay and is accessorised with Azla SednaEarfit tips. We'll see below if all this helps the Helios to sound as its price and features would suggest.

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I want to thank Symphonium Audio for giving me the possibility to test their product. But, specially, I want to thank SenyorC from Acho Reviews channel, who very kindly proposed Vertex ( and me to participate in this little tour.
Below I link his reviews and videos, in recognition of his work.

Acho Reviews

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  • Driver Type: 4 BA drivers.
  • Frequency Response: 12Hz - 24kHz, ± 2 dB
  • Sensitivity: 104dB/Vrms @ 1 kHz
  • Impedance: 8.5 Ω @ 1 kHz
  • Cable Impedance: 0.20 Ω (2.5mm), 0.25 Ω (3.5mm), 0.28 Ω (4.4mm) @ 1kHz
  • Cable: 26 AWG Pure OCC Copper
  • Connector Jack: 2.5mm, 3.5mm, 4.4mm
  • Capsule Connection Type: 2Pin 0.78

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Sources and Handling

Normally, I have never included a section on the use of sources and their pairing with the IEMS to be reviewed. But, on this occasion, I feel I must share my experience of using the Helios with many of my sources. Mostly because it has not been pleasant. One of my favourite balanced sources is the Tempotec Sonata E44. Connected, as I usually do, to my PC, all I could hear was noise, interference, even crashing the Foobar2000, which I use as a player. I switched to the Hidizs S9 Pro with a similar result, then to the Earmen Sparrow with no improvement in performance. Then I opted to use the Hidizs DH80s connected to the Tempotec V1-A. Nothing improved.
Then I decided to listen to my colleagues who had reviewed this product before. With an impedance of 8.5Ω, it is clear that you have to use sources with very low output impedance and all the ones I have used have been. But I have not found this to be the problem. I might think that the USB ports on my PC are very noisy, but I use several types of USB ports, including additional PCI-Express cards. In the end and recommended by my colleague Vertex, I used the Qudelix-5K and both via Bluetooth and PC, the sound was very good. Using other sources with transistors, such as the Burson Audio Playmate also proved to be adequate. But, in the end, I will stick with the combination of the S.M.S.L Sanskrit 10th MKII + iFi ZEN CAN. Other sources I used were the Earmen TR-Amp, the DAP xDuoo X3II, both with acceptable results, and the E1DA #9038D, with ambiguous performance. Sometimes as good as the Qudelix, sometimes as bad as the other conflicting sources. And it is worth remembering that the #9038D is very powerful and has an ultra-low output impedance.
Continuing my search for other compatible sources, I have also used my smartphone connected to many of the above dongles. I have to admit that the performance was superior to the previous tests (my PC and the Tempotec V1-A), but I could not get a pure or interference-free sound at all times.

My thinking is that this flies in the face of what is written on their website and I quote literally:

Infinite Linearity
Featuring Filtered Linear Attenuation Tuning (FLAT) Technology, a propriety circuit developed in-house with Subtonic, Helios will not be affected by impedence mismatch due to difference in source used. You will be able to listen to the same unimpeded sound regardless of the device you are using.

I don't know how it will have worked out with other users, but with me, the above paragraph does not match what I have encountered in my tests.

On the other hand, with the impedance and that sensitivity, you may need to use a source that provides a good voltage as well as a large current supply, it is not easy to drive these Helios, if you like moderately loud sound.

Finally, with the intention of avoiding mistakes, I have also tested the Helios with one of the best cables I have, the ISN C16, without finding any difference, nor any improvement.

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The package received consists of two items, a black cardboard box and a black leather-like zippered case. The case has a soft, grey interior with flaps on the sides, like a pouch. In it is the cable with 2.5mm connector. The case is relatively small and the cable and IEMS assembly fits somewhat snugly. The other element, the black box, measures 173x111x47mm. It has the brand name written in the centre, in medium-sized letters, and the model name on the base, in smaller letters. The ink used is white. On the left side there is again the name of the brand and the model. On the right side there are three explanatory icons. On the back side, on the base and in small letters, it says "Made in Singapore, Lah". All of this is written on a cardboard cover that slides up or down, leaving a completely black box uncovered. After removing the lid, a rectangular metal plate with the brand name and model can be seen on the bottom half. On the upper half is a cylindrical, flat, heavy, all-metal box with a screw-on lid, on the surface of which is written the brand name in light relief. Both elements are protected by a foam mould, covered with a velvety surface. As I said, the box is quite heavy, with an inner foam base, as is the top of the lid. After unscrewing it, you have access to the two capsules, a cleaning tool with fork and brush, as well as a copper cable with a 4.4mm plug.
Finally, in a somewhat hidden section of the case, there are the silicone tips. In the narrow base of the box there is a loop, if you pull it open a small drawer containing a metal plate with the serial number engraved on it and the silicone tips. There is a set of three pairs of Azla SednaEarfit and another 3 of Symphonium itself. In summary, the complete contents are:

  • Both capsules with Azla SednaEarfit tips.
  • One 26 AWG Pure OCC Copper cable with 2Pin 0.78 connectors and 2.5mm plug.
  • One 26 AWG Pure OCC Copper cable with 2Pin 0.78 connectors and 4.4mm pin.
  • 3 pairs of Azla SednaEarfit tips, sizes SxMxL.
  • 3 pairs of Symphonium tips, size SxMxL.
  • 1 cleaning tool.
  • 1 metal serial number card.
  • 1 metal screw box.
  • 1 zipped case.

As I said, the zippered case looks like an additional accessory, because it is not in the box. It is just the right size to hold the cable and capsules securely. The metal box is a bit bigger, but as a carrying case it is heavy and bulky.
6 pairs of tips seem too few to me, even though one set is from Azla.
The cables are OK, but I would have preferred one 3.5mm and one balanced. Although I think one is another additional accessory.
All in all, a sober packaging that is appreciated, but with minimal accessories for so much money. It has to be said that, for my taste, the metal plates are superfluous, I don't see any use for them. They could have replaced them with more tips or other things.

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Construction and Design

The capsules are made of a variant of the stronger AL6061 aluminium alloy, called T6. They are complete black and their shape has a tendency to an equilateral triangle, but with some rounded sides and corners. The surface has a slightly sandblasted texture. The outer face is flat and on the side of the base is written 'Symphonium' on the right capsule and 'Helios' on the left. The letters are capital letters in white ink. At the top corner is the 2Pin 0.78mm connection, mounted on a transparent plate and embedded in the body of the capsule. The rim mixes flat faces with rounded corners. The inner face has a flat side that slopes down towards the nozzle. The mouthpiece is relatively long, with a length of 6.5mm and a diameter of 5.75mm. The length of the nozzles is still somewhat longer because they are mounted on an inclined cylindrical base. They are protected by a pair of thick, metallic grids. Despite being made of metal, the capsules are not very heavy.
The cable has 4 stranded strands of 26 AWG Pure OCC Copper, covered with a transparent plastic shield. The sleeves of the 2Pin connectors are black cylinders with a red or blue ring, depending on the side. The connections are straight and uncovered. There are no ear guides. The integration of this cable with the capsule is not very adequate, as it is very long, with the base of the 2Pin exposed, giving a rather poor integration sensation, aesthetically speaking. The pin is a black metal doughnut. The splitter piece is a cylinder bevelled at the ends and depressed in the middle, but with a rounded shape. Very similar in shape is the jack connector sleeve, but the bevel is only on the end of the cable and the part near the connector is horizontal. The cable is not very thick, has a good feel and little tendency to coil. It is a detail that they specify the impedance of the cable.
Internally, they mount 4 BA drivers (although I have not been able to find it on their website, all the reviews say this). I think they have been designed by Symphonium themselves. They use the FLAT (Filtered Linear Attenuation Tuning) system, a proprietary circuit developed by Subtonic. They integrate a 4-way frequency crossover made with high quality components from Panasonic and Vishay.
The construction is good, the design is somewhat simple. Aesthetically they don't look like they cost what they are worth. The nozzles are a bit long. The set is good but I wouldn't single it out from other constructions, nor from other designs. I find them sober, flat, simple, but functional.

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Adjustment and Ergonomics

Such a long nozzle with an inclination that is not the most ideal, results in an insertion that can neither be deep nor medium, at least in my case. With a shallow insertion, together with these long nozzles, the capsules are somewhat separated from my ears. On the one hand, no part of the inner side touches my ears, only the tips. In that sense it seems good and comfortable, especially because the tips I use fit my anatomy very well and the capsules don't move. But the floating feeling of the tips is not what I like the most. I would have preferred more integration with my ears.
On the other hand, the passive isolation I get with my foam-filled tips is very high.

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In my opinion, the Helios have a lower-case u-profile, with emphasis on the sub-bass, high mids and first half of the treble, with a good punch of air. The descent from the sub-bass is fast, cleanly transitional and the high mids are sustained in a fairly linear fashion well into the treble. Although the treble feels well extended, it is not an eminently bright profile because there is a great deal of control in that response. There is an emancipated clarity, with a clear, relatively bright timbre, but tuned to be pleasant yet sparkling. I can't make the profile feel sharp, because it has a good balance, albeit with eminently cool features.

Symphonium Audio Helios.pngSymphonium Audio Helios vs Yanyin Aladdin.png


The easy test to tell whether the bass is coming from a BA or a DD is to play pure tones from 20 to 50 Hz. The result is eloquently unambiguous. And, in this case, it is no different. But the better these notes are reproduced, the better the quality of the BA driver. Here you can see that the resulting typical reproduction is clearly perceptible up to 40 Hz. This sound is more like a vibration than a low-frequency oscillation and is audible than sensory. But from this frequency onwards the sound becomes more natural, it loses that high degree of colouring and becomes a more natural sound, but without sounding like a good DD. In my opinion, there is that classic BA timbre in the bass, but I can't deny that, when playing real music and not those pure tones, the result is more normal and natural. Apart from this test, which is really critical and perhaps even unusual, the low end response is very good. But I expected no less from a $1000+ IEMS. Actually, I would have preferred a hybrid configuration with a DD driver for the bass, but this is a personal matter and now it's time for the classic low end review.
Again, the low end has a moderate colouration that fades away as the frequencies increase. The punch in that lower part is emphasised, which makes this effect more audible, although it shouldn't be. Even so, the response is smooth, with a rough texture, the result of vibration. In this sense, this characteristic is more beneficial than harmful, as it gives it a descriptive touch that I like. It is very positive that the Helios hold up very well in sub-bass saturated, poorly etched and dirty LFO playback, which denotes great quality. Not only do they hold up well, but they also have a remarkable level of energy, something bass-lovers will appreciate, if they are kind to their timbre.
In terms of technical capabilities, the bass is very fast and the decay is also fast, which makes each hit very concise, very defined and without aftertaste. It is clear that there is no bleed from the lows to the mids, which is the reason for this speed and the tuning focused on the lower end. These characteristics, on the other hand, slightly limit the width and depth of the scene, as they are not very expansive in this area. The recreation of planes is not very remarkable either, despite the precision of the notes and their level of accuracy.

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I find that the mid-range possesses an analytical capacity that makes them very neutral, clean, precise, concise and dry. They can even sound too sparse at times, which makes them lose their three-dimensionality.
The first half of the mid-range is lighter and provides a thinner, less dense sound, which gives less body to the male voices and instruments better represented there. This is something that still enhances the sense of precision and finesse of the notes, increasing the clinical, high-resolution feel. These thin, sharp notes are spaced well apart, but together they do not add up to establish a corporeal substratum that expands the sound and gives it cohesion. It is a concrete and precise representation, which can even be enhanced with cooler sources, or moderated slightly with warmer sources, but without ever appeasing this character.
The second half has an emphasis that rises evenly, but carefully, to reach a level where clarity becomes canon, the treble shining with splendour, fullness and extension. It is clear that the union of this profile with the analytical character, causes a very pronounced sensation of cleanliness, with a high level of transparency, which squeezes the notes even more. There is not a hint of darkness, nor is there warmth, the execution is explicit and effective, without embellishment, beyond the accuracy and straightness of the notes. I must comment that I like the analytical sound, but I would have liked to have had a fuller and wider sound, not so rinsed and polished.

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The treble is the area I like best, it has the necessary point of excitement and is cut off at the critical moment, where sibilance is kept at bay. Yes, there is no doubt that brightness is felt and that all notes have flashes, but the speed is such that such bursts are very fleeting, offering a sense of almost absolute control. Add to this the linearity of its extension, and the high end never feels omitted, but is an important protagonist within a sound that seems destined for its own showcasing. The extra-resolute character of the Helios finds its best asset in this range and that enhances the final result. There is no aftertaste and the characteristic dryness is now a virtue, generating a quick, fleeting and ephemeral beauty that disappears before it gets annoying. The sensation of air feels a little more limited, but it is capable of lending a volatile character to the elements in this range, though not enough for the rest.

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Soundstage, Separation

As already mentioned, the sensation of such a well-defined sound and its expansive limitations offer a relatively wide scene, with good depth and better headroom. But the amount of vapour and the ethereal feel is perceived as restricted. Despite the high level of resolution and note definition, the lack of substrate does not generate enough physical sensation to personalise instruments or voices within the soundstage. Thus, their placement is accurate, but their representation lacks weight, body and three-dimensionality. There is a remarkable level of separation and a great sense of transparency, the sound is very clean and diaphanous, but its development is observed in only one direction, forward, as if it were slightly channelled, focused.

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As they say, there are some delicacies that are not meant for a pig's snout. Perhaps this is one of them. I am not used to trying products in this price range, but when I have been able to, I have seen why they are so expensive. I haven't had that feeling with Helios. Lately, I have been reviewing IEMS that cost 4 times less, whose performance is excellent compared to the price/performance ratio of the Helios. Apart from the treble, analytical ability and tuning, I can't find anything so excellent that I would recommend them with my eyes closed. Are the Helios good? Yes, undoubtedly. But why use a BA for bass when there are outstanding DDs for this range, which clearly surpass what this product offers? Another thing I wanted to find is a more realistic sound. In my opinion, an analytical sound that crosses the barrier of superior quality is found when it merges with naturalness. This is not the case here either. Although the level of detail is quite high, I don't find it differentially superior to others in my humble collection, not even to the memory of other IEMS in the same league, which I was able to test in the past. Perhaps my memory is weak, but there are other conflicting drawbacks to this model, such as the difficulty of pairing with my usual sources, the presence of parasitics and noise that I have encountered. It is possible that to move this model, a source to match it is necessary. But this is contrary to the FLAT technology used in this model. I can't forget about the packaging either, the leather box looks like an additional accessory, which on top of that is small. The metal box is very heavy and the accessories are few, if you compare them, for example, with the Dunu Falcon Pro. Who can tell which is the expensive one and which is the cheap one? Yes, because the external design is not spectacular either, but I don't really care if the sound is up to the mark.
I don't intend to be critical of this model out of cliché, snobbery or to differentiate myself from the others. I just think what would have happened if I had bought this model for 1099$, instead of testing it on a tour. I'm sure that after having tested it in every possible way, my disenchantment would have been greater and I would still be trying to look for the positive side. Fortunately, I don't have to do that here.

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Sources Used During the Analysis

  • Xiaomi Redmi Note 8 Pro
  • Tempotec Variations V1-A
  • Tempotec Sonata E44.
  • Earmen Sparrow.
  • Earmen TR-Amp.
  • Hidizs DH80S.
  • Hidizs S9 Pro.
  • E1DA #9038D.
  • Qudelix-5K.
  • Burson Audio Playmate.
  • S.M.S.L Sanskrit 10th MKII + iFi ZEN CAN.


  • Construction and Design: 80
  • Adjustment/Ergonomics: 75
  • Accessories: 70
  • Bass: 82
  • Mids: 84
  • Treble: 94
  • Separation: 89
  • Soundstage: 80
  • Quality/Price: 60

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You can read the full review in Spanish here:
Last edited:


500+ Head-Fier
Icarian Flight
Pros: great bass performance from BAs, great technical performance overall, treble extension, midrange tuning, imaging
Cons: very industrial form factor, 2-pin connector design fraught with peril, may be too bassy for some


The Symphonium Audio Helios is an all-balanced armature (BA) in-ear monitor (IEM) using four BAs per housing. The Helios retails for $1099. I received the Helios through a review tour organized by Symphonium Audio. I had the Helios for around two weeks before writing my review. I am responsible for shipping costs to the next reviewer on the tour, and I am not being otherwise compensated for writing this review.
I do count Toranku, one of the Subtonic collaborators responsible for the tuning of the Helios, as a formative influence on my reviewing style, and I have had a uniformly positive experience in my personal interactions with him. I strive to be as objective and unbiased in my reviews as possible, but this is worth stating upfront regardless.


I have used the Symphonium Audio Helios with the following sources:
  • Qudelix 5K
  • E1DA 9038S
  • Hidizs S9
  • Reiyin DA-PLUS


I have tested these headphones with local FLAC and Spotify Premium. Visit my page to get an idea of what I listen to:
XenosBroodLord’s Library |



The Symphonium Audio Helios comes in plain black cardboard packaging with minimal branding.

The package includes a weighty polished metal circular carry tin embossed with the Symphonium Audio logo. The top and bottom of the case are lined with black felt. This case is too small in my opinion. Trying to fit the IEM in the case with the cable attached is a surefire way to bend the extruded 2-pin connectors. In addition, the threading for the screw-on lid is occasionally frustrating to properly orient and is very noisy.

The Helios review unit I received included two balanced cables (2.5mm and 4.4mm) and a leather clip to secure the cable not currently in use.
The Helios includes three pairs of generic silicone eartips (S, M, L) and three pairs of Azla Sedna Earfit eartips (S, M, L). The omission of at least one pair of foam eartips is regrettable at this price point.

The Helios also includes a credit card-sized metal plaque etched with the unit serial number, a cleaning tool, and two logo stickers.



The Symphonium Audio Helios has bulky aluminum housings with triangular faceplates. There is a faint seam between the faceplate and the housing body. “Helios” is printed on the left faceplate and “Symphonium” is printed on the right faceplate in the same bold white font seen on the packaging. There is a single pinhole vent on each shell adjacent to the 2-pin connector. The nozzles do not have a lip to secure eartips but are thick enough that I did not encounter any issues with eartips getting stuck in my ears when removing the IEMs.
The 2-pin connector housings extrude slightly from the body of the housing, but the actual plastic surface of the 2-pin host connector is nearly flush with the surrounding metal enclosure. This is confusing given that the included 2-pin cables seem to be designed for use with a much more recessed 2-pin host connector. This contributes to the likelihood of the 2-pin connectors being bent in use or in storage as referenced earlier. The 2–pin cable juts away from the ears at a pronounced angle rather than falling closer to the skull as is seen on most IEMs, an issue exacerbated by the extended 2-pin connectors. Perhaps because of this, there are no earguides on the included cables.



The cables themselves are very attractive, with high-quality copper wire and matching polished black metal hardware for the jack housings, Y-split, chin-adjustment slider, and 2-pin housings. There is minimal strain relief above the jack, but none at the Y-split.


The Symphonium Audio Helios is intended to be worn cable-up. The insertion depth is on the deeper side. The Helios is far from the most comfortable high-end IEM I have used but is tolerable for extended periods. Secureness of fit and isolation are above average.


My measurements of the Symphonium Audio Helios can be found on my expanding database:
Symphonium Audio Helios — Squiglink by Bedrock Reviews
My measurements are conducted with a Dayton iMM-6 microphone using a vinyl tubing coupler and a calibrated USB sound interface. The measurements use a compensation file derived from relating my raw measurements to published measurements from Crinacle and Antdroid. These measurements should not be directly compared to IEC-compliant measurements, particularly above 6 kHz.


The Symphonium Audio Helios somewhat expectedly closely hews to the Toranku target, which adjusts the Harman target to track more closely with audiophile preferences. It can be roughly characterized as neutral with a sub-bass boost.
While the sub-bass elevation is substantial, it is not as boosted as that of the Moondrop Variations, which was bass-boosted to the point of limiting its versatility. The bass delivers an impressive sense of note weight, slam, and impact for an all-BA set. Sub-bass extension is superb. Bass texture is also very good, especially considering the driver configuration. Complex, dense instrumentation is rendered with speed and precision. The bass is cleanly delineated from the midrange, with no mid-bass bleed.
The Helios’s midrange tuning differs substantially from the Harman target, and for the better. The pinna elevation is more restrained, and the presence region tapers off more gently. The pinna elevation is also centered around 2.5 kHz rather than the 3 kHz commonly used with Harman-ish tunings.
The biggest advantage of this tuning is greater coherency between vocal delivery and midrange instrumentation. On a lot of IEMs with Harman-ish tunings, midrange instrumentation, particularly rhythm guitars, can disappear under the vocal presentation. This is not the case here. Vocal intelligibility for both male and female vocals is still excellent, but both are better integrated into the overall image than is common for a Harman-ish tuning. The presence region is clear but comfortable. Electric guitars growl without sounding strained or over-distorted. The Helios is not sibilant to my ears.
The Helios’s treble region aims to be engaging more than it tries to be smooth. This is in line with my tastes, but the lower treble emphasis may be too much for some listeners. The overall balance is weighted towards the lower treble, but the upper treble extension is excellent nonetheless. There is ample sparkle and air. Resolution and detail retrieval are excellent. The soundstage is expansive, and layering is likely the best I have ever heard. Instrument separation is very good. Transient delivery is well-defined, and micro-dynamics are perceptible.


The biggest difference between the Symphonium Audio Helios and the Moondrop S8 is in the bass technicalities. The Helios offers moderately superior bass performance to the S8 in most respects. The Helios has superior sub-bass extension, notes have more substantial weight and there is a greater sense of impact. The Helios’s bass response is more textured and dynamic. The S8 offers crisper, more defined note articulation, and better internal note resolution. The S8 suffers to some extent from the issues common to vocal presentation with Harman-ish IEMs, while the Helios does not. The Helios also has a more natural, less plasticky midrange timbre. The Helios has slightly better upper treble extension than the S8, but the S8 has comparable if not slightly superior detail retrieval. The S8 has a larger soundstage and greater instrument separation. Overall, the S8 sounds thinner but more tonally coherent than the Helios. The Helios is much harder to drive than the already demanding S8.


The Symphonium Audio Helios is a power-hungry IEM and requires a balanced source device or a very powerful single-ended source device. I did not detect hiss with any of my sources.



The Helios is an astonishing first effort for Symphonium Audio and Subtonic and deserves to be considered a worthy contender in its price range.
The Symphonium Audio Helios can be purchased below:
Helios — Symphonium Audio
If you enjoyed this review, please consider checking out my blog at
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Reviewer at
The Brightest Kilobuck Star
Pros: - high clarity signature with class leading treble extension
- above average BA bass and dynamic contrast
- excellent imaging
Cons: - fit will present an issue for those with smaller ears
- a leaner sound signature which could use with more mid-bass

This review was originally published here on


Imagine the following scenario. A flagship IEM is released to lots of hype. Said flagship IEM turns out to actually be pretty mediocre, and the hype subsequently dies. Rinse and repeat, plus stack on a couple hundred bucks more for the next big thing. Well, welcome to the flagship IEM world! Having experienced numerous cycles of this myself, it's becoming increasingly rare that I get excited about an IEM; however, there is one IEM I've been eager to hear for some time now: the Symphonium Audio Helios. Symphonium is a small Singaporean brand, and the Helios is their 4BA flagship IEM. You heard me right. Amidst the omnipresent drivers war and the staggering, ever-increasing cost of flagship IEMs, Symphonium has opted to take a more graceful approach with the Helios that clocks in at a reasonable $1100.

The Helios was also developed with consultation from Subtonic. Subtonic is an upcoming Singaporean audio brand; a partnership between several audio enthusiasts including Toranku of Head-Fi fame and Leneo of Audio Discourse. In the interest of transparency, I regularly converse with these individuals and, as jaded veterans of the Singaporean audiophile scene who have heard hundreds of IEMs, they are some of the most critical listeners I know. That in mind, I don't think it was ever a question of whether the Helios would be good, but rather how good?

Spoiler alert: I bought my own Helios within roughly 24 hours of hearing the tour unit.

IMG_1267 2.JPG

Source & Drivability​

All critical listening was done using my iBasso DX300 and iPhone X with lossless files. The stock cable and stock tips (Azla SednaEarfit and Syphonium silicone tips) were used. Personally, I found the Helios to take a good amount of power to drive, sitting at around 45% volume on my iPhone X to reach my comfortable listening volumes (~70dB).

The Tangibles​

The Symphonium Audio Helios arrives in a discreet, black cardboard packaging. Upon removing the outer sleeve and cover, you'll be presented with the Helios' aluminum case nested in the center and a small assortment of accessories in a panel that slides out from the bottom. Here's what's included in total:
  • 3x Azla SednaEarfit tips
  • 3x Symphonium Audio silicone tips
  • Aluminum hockey-puck style case
  • Metal placard with SN
  • 0.78mm 2-pin cable
Symphonium Audio Helios Review |

I do wish some more care was put into the hockey-puck case. I like the general build of it and the large O-ring is a unique touch for waterproofing, but the threading could use some work. It's a tad screechy and it has a tendency to cross-thread when I'm initially screwing it on. Just something that I watch out for as someone who's played with a lot of high-quality knives, flashlights, and gear of that nature. The included cable is a standard 2-pin 0.78mm one, but it does not have pre-formed ear hooks for reasons I'll explain shortly. It is supple and non-microphonic.

Symphonium Audio Helios Carrying Case |

Moving onto the IEM itself, the Helios is big, and I believe that the sheer size will present the biggest limitation for prospective buyers. It sticks out of my ears slightly, and most ear guides with other cables wrap themselves over the middle of my ear instead of neatly nestling into the crevice between where the ear meets the head. I imagine this is why there is no pre-formed ear guide on the stock cable. When I asked about the size of the IEM, I was told that Symphonium Audio had to use larger tubing to achieve the desired treble extension and that large, high-quality capacitors were used too. Luckily, I don't have any major issues with comfort once I get a seal. Do note that this IEM forms a very tight seal; it definitely has above average isolation once you achieve a deep fit with it.

Symphonium Audio Helios In-ear monitor headphones Review |

Sound Analysis​

The measurement below was taken off of an IEC-711 coupler. There is a resonance peak at 8kHz; as such, measurements after that point should not be considered entirely accurate. You can visit the site below for comparison to other IEMs that I have measured.

Symphonium Helios Review |

The overall tonality of the Helios can be considered neutral with sub-bass boost. From the bass up until the lower-midrange, the Helios tracks the Harman 2019 IEM target very closely. But while BAs are generally maligned for their limp bass dynamics, a notion that becomes increasingly apparent as one begins exploring the upper-echelons of the IEM world is that not all BAs are created equal. Indeed, the Helios is a standout in the BA bass department. This is partly due to its tuning which is concentrated almost solely in the sub-bass regions, therefore emphasizing a high degree of cleanliness and never infringing upon the lower-midrange. But the Helios is no less a slouch in the intangible department either. It actually slams, so much so that I wouldn't mind putting it up there with my beloved 64 Audio U12t. While I don't find it quite as "organic" - the Helios' bass texture leans more dry than the U12t, perhaps due to a lack of mid-bass - the Helios sets the standard at a kilobuck for BA bass.

The midrange of the Helios continues to follow the Harman target closely throughout the lower-midrange. That in mind, despite the more gentle approach taken to the pinna compensation and the upper-midrange, the Helios' note weight definitely skews slightly thin to my ears. Is this necessarily bad? Not at all, but this is where tonal preference will divide some listeners on the Helios' tuning. Personally, I think it would benefit with some more warmth. I also want to say that the Helios is almost too resolving for its own good here. While I don't hear any exaggerated instances of sibilance on my usual test tracks like Girls Generation's "Flyers" at 0:46, transients seem to have a slight edge to them that makes even very small instances of sibilance, such as on Loona's "Voice" from 0:25 to 0:30, pop more than I'm accustomed to. This is especially apparent when listening with the Azla Sedna tips.

Likewise, the Helios' treble is something of a double-edged sword. I cannot deny that it is wonderfully extended and mostly smooth without any egregious dips or valleys in sine sweeps. But here's the not-so-favorable side of that sword: the treble of the Helios teeters on abrasive to my ears. I have to imagine that this abrasiveness is partly baked into excess air, as swapping off the Azla Sednas for the Symphonium ear tips largely mitigates this issue and brings it within "this might be the best treble response I've heard of a kilobuck IEM" parameters. Incidentally, when I dropped the tour unit off with Super*Review, he had very similar impressions between the two ear tips. But either way, the timbre of the Helios's treble still seems somewhat distinct from the bass response which is surprising given that this is an all-BA IEM. This sentiment applies to the midrange to a lesser extent; at times, I could even mistake the Helios for sounding more like a hybrid than it does a BA IEM!

Symphonium Helios Review |

You might see where I'm going: the Helios doesn't sound as coherent as I'd like. As with IEMs like the Thieaudio Monarch and the Moondrop Variations, this feeling is ostensibly baked into the tuning to some degree. From the Helios' razor-sharp bass shelf, its slight dip at 200Hz, and to its excellent treble extension, it all culminates in a more segmented if not clean presentation. Furthemore, I get the impression that Symphonium and Subtonic have indexed too heavily for individual aspects of the Helios' sound and that their IEM has missed the forest for the trees so to speak. Along these lines, the midrange brings out unwanted micro-detail, the treble has too much air resulting in slight harshness, and the subsequent timbral inconsistency is partially because the bass is so good for a BA. For what it's worth, these are definitely some of the better problems to have. Your average listener probably wouldn't pick up on the coherency issues, and the excess treble air would likely be a boon for most listeners.

Technical Performance​

It doesn't hurt that the Helios has a strong technical foundation with almost zero weaknesses in the departments I usually index for. Let's begin with detail. Detail is not stunning, but it is pretty darn good. As one might imagine, the Helios' excellent treble extension aids perception of reverb trails and sonic minutia that would otherwise be lost on lesser transducers. Take for example that faint ring to the backdrop of Taeyeon's "I Found You" which usually only presents itself to me on my two-channel speakers. Transients are also sharp without noticeable blunting thanks to the clean, segmented tuning.

As for more latent intangibles, the Helios doesn't let up. Imaging is slightly out-of-head and the Helios sports sharper positional incisiveness than the Andromeda 2020 in A/B. This is especially apparent when it comes to left-right channel distinction. Vocals and instruments panned directly to the sides of Sawano Hiroyuki's "N0VA," for example, have a quality with which they float and wrap around the head oh-so-satisfyingly. Yup, the Helios actually has some backwards imaging! It follows that the Helios' layering chops are excellent, maintaining nuance between various instruments even on dense, epic-orchestral tracks like Thomas Bergersen's "Dear Mr. Alien".
Now, I normally don't mention dynamics - gradations in loudness - because 90% of IEMs aren't worth talking about for this metric, or only worth criticizing for their lack of it. But while the Helios does skew toward some unwanted loudness, it's also surprisingly dynamic for an IEM. For both macro and micro-contrast, the Helios takes top marks at the kilobuck level from this reviewer. Even in A/B with the Elysian Annihilator, one of the few IEMs I'd consider to have good dynamics, I was surprised to hear that while the Annihilator sported better macro-contrast and quicker transients, the Helios traded blows in the micro-contrast department. In general, transients on the Helios are quick with ample zest, and I find myself glued to the hard-hitting, intensive ride that is BoA's Deluxe album.

I know. It sounds out of character for such an unrelenting critic like myself, but I'm genuinely hard-pressed to ask for more in terms of technicalities. In fact, technicalities were my biggest point of contention before hearing the Helios, as I already had a rough idea of how the Helios would sound based on the FR graph. Suffice it to say that the Helios didn't disappoint. You (or at least certainly I) wouldn't know this IEM toted a mere 4BAs if it weren't for the product literature!

Symphonium Audio Helios in-ear headphones Review |

Assessment of Value​

Here's a shortlist of some IEMs that come to mind when we're talking about "the best kilobuck IEMs":
  • Campfire Audio Andromeda 2020 ($1100)
  • Hidition Viento-B ($1000)
  • Moondrop S8 ($700)
  • Sony IER-M9 ($1000)
  • Thieaudio Monarch ($730)
  • Unique Melody MEST/MEST MK2 ($1000/$1500)
Clearly, the Helios is playing in very competitive territory. There are many established IEMs circling the Helios that would be more than happy to take a bite out of it should it falter. Comparisons below were done via direct A/B where possible.

Campfire Audio Andromeda 2020: The Andromeda 2020 has a warmer, darker sound that makes its mark with its holographic imaging. In tandem with its lackluster BA bass and dynamics, the Andromeda 2020 is an IEM suitable for listeners who want an IEM to kick back with, to relax, and to soak in its unique presentation. The Helios has a leaner sound and demands attention, sporting aggressive dynamics, sharper resolution, and BA bass that actually slams. While I can definitely still see a case being made for the Andromeda 2020, I sold my Andromeda 2020 in favor of the Helios.

Hidition Viento-B: The Viento-B has some strong similarities to the tuning of the Helios, but in most respects, you can consider the Helios a Viento-B on steroids with more bass. The Helios has better BA bass, a more balanced midrange, and a more linear, extended treble response. Personally, while the Helios' treble toes the line, I found the Viento-B's treble to be outright abrasive. From memory, I find the Helios to be a solid step-up in the technical department too. It has better imaging (sharper positioning and soundstage size) and a more natural timbre with less intangible grit.

Moondrop S8: The S8 tracks to the Harman Target more closely in the upper-midrange, and then eschews the target for good amounts of air like the Helios. Head-to-head, I do find the Helios to have even more sparkle and air than the S8, as the S8 has something of a minor recession in the mid-treble. Detail between the two, however, is comparable and they trade blows for their layering chops in A/B. I'd say the S8 even has a slight edge in terms of coherency. Where the Helios clearly pulls ahead, though, is in its impactful dynamics and standout BA bass. The Helios also sounds more open owing to less mid-bass and perhaps the larger nature of its shells. For me, the Helios is a step ahead in the technical department, as it should be for $400 more.

Sony IER-M9: The IEM that many readers will recall that I've dubbed the kilobuck benchmark in the past, so it was only fitting that I A/B these two IEMs to confirm my thoughts on the Helios. As I alluded to earlier, I prefer the bass tuning of the Helios. That said, I was more pressed to decide between the two for bass intangibles; the IER-M9's bass still maintains a more DD-like tactility to my ears. But where the IER-M9 really draws the short end of the stick is in its dynamics and treble response. It is a very flat sounding transducer and it's treble response, while delightfully sparkly, lacks appropriate initial impact to percussive hits. The Helios runs circles around the IER-M9 in the dynamics department and has a smoother, more airy treble response. Generally, the Helios also sounds considerably more open and has sharper resolution because of how warm IER-M9 is. I'm not sure if the Helios is actually more precise with instrument positioning, but these factors sure lend to that perception.
All that being said, when you throw the IER-M9's whole package into the mix - accessories, build, fit and a $100 price differential - I think you could still make a good argument for the IER-M9 remaining top dog. But on the basis of sound quality, I would attest that the Helios is better and noticeably so in A/B.

Thieaudio Monarch: It's not really a contest between these two IEMs, at least for me. They have a very similar tuning profile; the Helios just has more treble extension and presence in those final octaves. Where these IEMs part ways considerably is in the technical department. The Monarch has great macro-detail, no doubt, but its overall sense of detail, imaging, and dynamics are mostly just average for $700. It's certainly behind the Helios for me on those fronts. That's also ignoring the Monarch's coherency which is another step behind, despite the Helios not even being a stronger performer for that metric as I expanded upon in my sound analysis above.

Unique Melody MEST/MK2: The OG MEST and MEST MK2 are both very solid IEMs that have been met with lots of acclaim this past year. That said, I think they have some tough competition against the Helios. The OG MEST, with its uncanny sense of separation, might have a small edge over the Helios for imaging. But the OG MEST also has some compression issues to its midrange (which sounds quite digital) and its treble which has a tinny characteristic. The MEST MK2 fixes these issues to some extent, but trades some of the OG MEST's resolution and imaging chops. The Helios doesn't make compromises. It sports comparable resolution to the OG MEST and outclasses both IEMs in the dynamics department. That's not to mention the Helios' treble which is simply a step ahead of the ESTs being used in the MEST IEMs.

The Verdict​

There's no question in my mind that Symphonium has released a highly competitive IEM for its respective price bracket, one that is worthy of kilobuck benchmark status. Is it top-tier material, though? To be blunt, no. Not quite. It lacks that last leg of refinement which would place it amongst greats like the 64A U12t, the Empire Ears Odin, and the Elysian Annihilator. It's also not far and away better than everything else in the kilobuck space, or it wouldn't cost what it does. But is it...better? Yes, I think it is. There is a strong possibility it is the best sounding kilobuck IEM on the market today. In that vein, I have zero qualms giving the Helios my stamp of approval on the basis of sound quality. I think it's safe to say that Symphonium and Subtonic have a bright - a very bright - future ahead if the Helios is any indication of what they are capable of.


Reference Tracks​

  • Aimer - Hakuchuumu
  • David Nail - Let It Rain
  • Everglow - DUN DUN
  • Girls’ Generation - Galaxy Supernova
  • Illenium - Broken Ones
  • Joe Nichols - Sunny and 75
  • Keith Urban - Defying Gravity (2009)
  • Keiichi Okabe - Weight of the World (NieR:Automata Original Soundtrack)
  • Sabai - Million Days
  • Sawano Hiroyuki - Best of Vocal Works Remastered (2020)
  • Taeyeon - My Voice (2017)Tiffany - I Just Wanna Dance
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Ace Bee
Ace Bee
Is it possible to provide a comparison between this and 64Audio U6T?


Headphoneus Supremus
Pros: Excellent tuning and technical performance
Great dynamics
Good soundstage and imaging
Premium accessories
Cons: Low-Mids are a tad leaner and drier than I would prefer
Shell is large and nozzle angle creates challenging fit for some

The Helios is a new in-ear monitor product from a relatively new brand out of Singapore called Symphonium. The brand started out in 2017 and have three current products in their line-up. The Helios is their flagship product and comes in at about $1099 USD.

The Helios features four balanced armature drivers in a configuration that was developed in collaboration with some familiar faces for those of you who have followed Audio Discourse on YouTube -- mainly Leneo, Toranku, and Valoncia, who have started their own brand, Subtonic, and working on exciting new products together.

So that's a heavy disclaimer here, as I have worked on Audio Discourse's YouTube channel along side some of the folks involved in the creation of this product. This tour unit was loaned out to me from Symphonium directly, and this unit, along with a few others across the world, are being sent to various people in the community for feedback and impressions. All that said, as usual, I try to minimize as much bias as possible and have come into this with excitement, but also will provide my critical takes as well.

The Helios tour unit was sent with two copper-colored balanced cables in 2.5mm and 4.4mm varieties. These two cables are very soft and supple, and I find them both attractive and easy to use. They terminate in 2-pin connectors, and unlike most cables available, these cables do not have pre-shaped hooks.

The package also comes with a hefty round screw-on metal case that is polished metal and has a nice attractive and luxurious look to it. I am typically not a big fan of these screw-on round cases, but this one is pretty nice and I'd probably use it for storage at home.

The Helios shell design is a rounded triangular shape that isn't too dissimilar from others like 64 Audio and Tachijim's general shape and design. It is however quite large, and has a deep cavity and a longer than average nozzle that is also about 5.75mm in diameter. It is a bit on the large side, and is meant to for a deep insertion into your ear canal.

This can present some challenges to small-ear hole folks like myself. My left ear was able to get a deeper insertion than my right, as my left ear canal is just slightly larger and has a less sharp bend to it. My right ear is narrow and has an early and sharper bend, and so the nozzle length and diameter hits up against my ear canal a bit prematurely, and so no matter how deep I try to push it in, its maxed out due to the interference.

This causes the IEM to stick out a little further and at a kind of strange angle out of my ear. All that said however, with the right sized tips (in my case, SpinFit CP100 Small), I was able to get a tight seal and no real issues with pain or discomfort. It just didn't look or feel as secure as I hoped it would. I did not have the same types of pain I felt with the Moondrop Blessing 2 or the Campfire Solaris despite them also having similar fitment issues due to nozzle length, width, and angle.

Sound Impressions​

The Helios is a very well-tuned IEM that expresses a nice deep sub-bass presentation with clean lower-mids, and a smooth mid-range and treble response that falls in-line with my preferences. It can be perhaps a smidge bright but nothing really to concern about if I had to nitpick its tonal balance. I could also ask for just a little more mid-bass for extra warmth and smoothness, but man, this is a nicely balanced IEM that should be a great all-arounder for most genres.

If I had not known the quantity of the driver count, I may have thought there were more. The 4-BA configuration gets a lot of performance on this IEM, especially when I compare it to my beloved 4-BA Viento B Custom IEM. Yes, that one is several years old now, but it still stands strong in my opinion due to its fantastic tonal balance and coherence.

The Helios takes a similar tonal balance, but adds more sub-bass performance and adds a lot more dynamics to the overall quality. Bass has better texture and punch, and there's a nice amount of sub rumble that can be felt in my ears. It can slam when it wants to, though not as much as some other IEMs I have tried of course. The Monarch and Odin slams just a bit more for similar sounding gear.

Symphonium's mid-range is a perhaps a tad lean in the lower end, but has a nice balance in the upper mids where I don't find it too lean nor too hazy. Some people may find this to be a tad lean overall given the entire mid-range response as whole, but for me personally, I really enjoy this presentation, which is slightly dry, but very clean and clear, and strikes a good equal balance to the spectrum.

Treble, despite being perhaps just slightly more elevated than I like, is very smooth. There is a refined and buttery slickness to it that reminds me of the best EST IEMs (i.e. Odin), or even the all-BA ultra-warm and laidback Vision Ears sets like VE8 and Erlkonig.

One of the most noticeable sonic impressions I found with the Helios, for good or for bad, is that it sounds like some notes or some frequency range sounds a bit more forward and closer to my ear than others. The midrange just seems a little bit louder than the rest, which is good for those who enjoy hearing the mids, and for some reason, I do feel like I am turning this IEM a little higher up on the dial than others. Still, I do find that I prefer a slightly more relaxed tuning, and at times I do think that the Helios' mids are a bit aggressive.

The dynamics are very well done. Despite what I say in the last paragraph, there are nice varying levels of sound range here, and quiet moments come off quiet while loud moments are intense. It's not the best IEM in terms of macrodynamics I've heard, but it's definitely above average.

I spent a lot of time with the Helios in all sorts of genres and musical selections -- anything from old classic rock, to jazz, to electropop and folk, to country and to classical. It does well with all genres. I did find it best for some music specifically though.

For example, the subbass gain, tacked on with the nicely tuned upper-midrange is a great combination for the newest Chvrches album, "Screen Violence." The Helios does well with the electropop band's mix of deep subbass synths, and Lauren Mayberry's vocals. Even the dark, emotive track "How Not to Drown" featuring The Cure's Robert Smith sounds fantastic on this IEM.

I also spent a bit of time listening to Massive Attack and Morcheeba, trip hop legends from the past with the Helios, and again felt it works well with this electronic brand of music. Helios provides the much needed deep subbass this genre asks for, while also the electronic synthesized keyboard play on full display.

I will say that my most listened to music of late, trio-based jazz music, is probably the least favorite stuff I have heard on the Helios. Perhaps it's due to the lack of low-end warmth and just not having the real grunt of the double bass stand out, or the slightly forward piano notes being a distraction. This wasn't my favorite combination for the music I played with on the Helios, but again, it is still very enjoyable and well-resolving for this music.

The Kilo-buck Market Competition​

The Helios enters competition against a lot of other $1000-ish in-ear monitors that are very popular and very good. Here are just some of the ones I can think of off the top of my head:

  • Campfire Andromeda (2020)
  • Sony IER-M9
  • Hidition Viento
  • Thieaudio Monarch
  • Unique Melody MEST

There are definitely others to consider, but these are some of my top ranked IEMs and are tough, tough competition for a new company with a new kilobuck entry. How does it stack up?

The Helios' defining difference between most of these IEMs is their sub-bass elevation and focus with the exception of the Thieaudio Monarch, which have very, very similar tonality. The Helios is more coherent, with better clarity and resolution from my memory versus the Monarch, and the treble is smoother. It's also a little more costly at $350 more.

The Andromeda is quite a bit different sounding, while also sharing an all-BA setup. Both have good dynamics and resolution, while the tuning is where they go off on different tangents. The Andromeda is warmer with a significant amount more lower mids and midbass compared to the Helios.

The IER-M9 is also an all-BA setup, and just has a much different sound. It's ultra smooth and warmly tuned and darker. Its a more relaxing listen and does not have a sub-bass focus. It's been a while since I really listened to the M9, but I never felt the technical performance as compelling on first glance as I did with the Helios. It's not saying that much, but perhaps it the smoother, warmer nature of the M9 not showcasing its full talents.

Finally, the two IEMs I do own: The MEST and the Viento...

The Viento is also a 4-BA setup, but I feel its tonally better than the Helios with similar upper mids and treble, but less subbass and more mid-bass warmth. It gives a more even sound throughout, while the Helios has probably a bit better clarity, texture, and excitement.

The MEST is quadbrid, that also has a subbass focus, but not nearly as energetic as the Helios. It also differs in the uppermids, where the MEST is quite a bit more relax and darker, given the comparison between the two very different flavors.

Podcast Impressions​

This was a live stream video of first impressions of the Helios from myself (Antdroid) and Rush on our Youtube channel:


The Symphonium Helios is a really nice entry to the market. I am quite impressed by its technical ability and it has a tonal balance that I think will make it a favorite amongst many, especially those who enjoy electronic and other sub-bass focused music. It has a lot of the tangibles in place to really set itself as the top "neutral with sub-bass" top dog in a crowded marketplace. While I still prefer my Viento-B, another "neutral with sub-bass" IEM just a little bit more for its tonal balance and warmth, I can see the Helios being a close runner-up, but with better technicalities.

The biggest gripe I really have with the Helios is the shell design. It's large, requires deep insertion, and I'd prefer a lighter acrylic shell over the metal housing it comes in, but for many, this might not be a big deal.

The Helios is good and a solid-buy. I look forward to the next Symphonium and Subtonic collaboration as I hear there's something(s) even bigger down the road in the high-end market that gets me very excited. This is a teaser, and a really good one at that.

Audio Discourse Interview with the Creators​

Finally, to wrap everything up, here's an interview with Subtonic hosted from Rush of Audio Discourse's YouTube channel.


100+ Head-Fier
The best IEMs I have heard
Pros: - Tuning
- Detail
- Sounstage
- Imaging
- Subbass
- Treble
Cons: - Aesthetics (personal opinion obviously)
- Mid Bass not quite perfect for my tastes

The Symphonium Helios have been sent to me on loan from the company Symphonium Audio without a request for anything at all. I am very grateful for the loan of these IEMs as I would not have had a chance to try them out and they are certainly a set that have changed my view on IEMs as a whole, but more on that in a moment.

You can find the Helios on the Symphonium site here:

As always, my review and opinions will be as sincere and honest as possible but you do need to factor in two things, first that it hasn’t cost me anything to try out these IEMs and second, I may have already had some preconceived impressions of these IEMs before I even received them. Yo can also find this review in Spanish on and on Youtube.

I will explain more on why I may have some preconceived impressions in a second but as I am someone who believes in honest and unbiased reviews, along with sharing as much information as possible, I have arranged with Symphonium to allow me to send these on to two other Spanish reviewers who know nothing about them. The Helios will be going to both Vertex, who posts his reviews on the YouTube channel “Auricular ORG” (in Spanish), and to Cqtek, who posts his reviews in English and Spanish on, so please check out their reviews as well (I have no idea what they will think of them but I do know that they will share their unbiased opinions!).

Anyway, with that cleared up, let's get on with the Helios!



The Helios is a very recent release from a company called Symphonium Audio that has very few models and I only know about them due to the Helios and the talk of these IEMs in a Discord server that I am part of, along with people who worked on the design of the Helios and some reviewers whose opinions I have a lot of trust in.

This is the reason for the possible preconceived impressions that I mentioned, as I have heard nothing but praise for these IEMs since they started getting heard by those reviewers and by some other non-reviewers who have also had the chance to try them. It was actually quite an experience to see people try them and as soon as they passed them along, place their order for them. This obviously made me expect something great from the Helios, as there is no better positive publicity than people hearing them and then spending 1000€ to own them.

And that is another part of my impressions, I have never experienced a 1000€ set of IEMs before. In fact, it wasn’t too long ago that I said that 100€ was my limit for a set of IEMs and although I have broken that limit a couple of times, I am still a long way from having spent such an amount on a set of IEMs. The main reason is that I always prefer headphones, however, I have started to realize that I do use IEMs more than headphones, mainly due to the heat here for the majority of the year, so I have been more open to higher priced IEMs lately (although I still haven’t made the commitment).

All this is basically nothing to do with the Helios but I thought I would include this information as it gives you an understanding of where I am coming from with my impressions of the Helios, which I can already say is the best set of IEMs I have ever heard.



I am not 100% sure if what I have received is actually the same as what is received in a retail set of these IEMs, as I said, these are a demo unit, but I think that things like cables can be chosen when purchasing from Symphonium.

This set arrived in a black box, which I understand is the retail box, along with another case containing a second cable, wrapped separately.

The extra case is a very nice travel case which is (imitation) leather on the outside, sporting the Symphonium logo, with a nice furry interior. As I said, I am not sure that this case is included with the retail version but I have seen that it is available on the Symphonium webstore for $10 and it really is nice to have the lined interior. Inside this travel case they included a 2.5mm balanced cable.

Inside the main box we get a rather special aluminum storage case, which is round and has a screw off lid. I say this is a storage case as I don’t think I would personally use it for transporting the IEMs due to the size and weight of it, but again, it is very nice and does make it seem like you are receiving something special. The round case is located at the top of the box and has a metal plaque underneath that reads Symphonium Audio Helios. This presentation is rather simple but elegant, again, making it seem like something special.

Inside the storage case are the IEMs, a 4.4mm balanced cable, a small cleaning brush and tool, along with a few Symphonium Audio stickers.

The bottom end of the box has a small drawer that slides out to reveal another metal plaque with the serial number engraved, under which we find 6 extra sets of silicone tips, 3 sizes of large bore and 3 sizes of small bore. As this is a demo unit and I already have hundreds of tips in different sizes and styles, I haven’t actually used the included tips.

As far as the presentation, that about sums it up. Again, it is rather simple but elegant and includes enough accessories, although an unbalanced cable would have been nice but that will depend on the source that each person is planning on using.


Build and aesthetics…

Starting off with the IEMs themselves, they are very simple rounded triangles, all black, with Helios on one side and Symphonium on the other. To be honest, they are nothing much to look at, they are a simple shape and finish that does not jump out as being anything special, they certainly aren’t something that screams “expensive” to someone who doesn’t know IEMs, which can be a good thing depending on your use case.

They are also quite large and have a fair weight to them, with quite a long nozzle that is also on the larger side (although not to the extent of some nozzled like those of the iSine or Blessing). I found that a lot of tips didn’t slide all the way to the end of the nozzle, making the Helios stick out from my ears a little too much, although they still weren’t uncomfortable in this way. However, they are meant to be used with a deep insertion, meaning that I needed to select tips that are a little longer and also of a smaller size (as the seal happens further inside my ear). To be honest, I am not a great fan of deep insertion but they still weren’t too uncomfortable even when pushed deep.

The rest of the contents are of good quality, the accessories are great, as I mentioned, and the cables are nice. I guess my only complaint, which is not really a complaint, is that the cables do not have preformed memory wire or ear hooks, but that is not my complaint (I actually praise them not being preformed), it is the fact that the 2 pin sockets on the IEMs do not have a guide for the connectors and as the cables are not preformed, it makes connecting them out of phase very easy. This is easily overcome by looking at the channels on the connectors themselves, making sure they are the correct way round, but I can see people making mistakes and ending up with left and right out of phase by accident.



So, I already said these are the best IEMs I have heard. That is obviously enough to know that my impressions of sound are very positive, but that still doesn’t mean that they are perfect for everyone, or that they are even perfect for me.

I am going to go through my usual steps as far as sound but I want to point out beforehand that any negatives are minor and they are relative to what I want from a 1000€ IEM, not because the IEMs have any faults themselves.

As I have said with reviews of headphones, once we reach a certain sound quality, the rest is more about preference. That doesn’t mean that all headphones or IEMs above a certain price point are great, there are some that don’t hit the “certain quality” mark, but that is definitely not the case with the Helios, they surpass the that “certain quality” with ease, so it puts them in a zone where personal preference becomes the main deciding factor.

Starting off with the subbass, it is excellent.

Ok, I guess I better be a little more specific :) The extension of the subbass is great, reaching far lower than my hearing range, providing plenty of rumble but keeping it very clean and articulate, never seeming to lose control over even the lowest frequencies.

Now, I already knew what the measurements of these IEMs looked like way before I got them, and also heard praise for the subbass, but even so, I was very surprised. As I have mentioned many times, I am not a bass head and the graph of the subbass would place these well over my preferences, but the sound doesn’t. The cleanliness and presentation of the subbass means that the power to rumble is there, but it doesn’t just add it to everything, it just presents what the track needs at each time.

I don’t think I have mentioned yet that the Helios is a 4x BA set up, which is something that doesn’t really attract me on paper. I am a lover of dynamic driver bass, probably due to the fact that I have spent all my life listening to bass from dynamic drivers so it is what I find natural. In the case of headphones, I said that the HE1000se (and now possibly the Arya Stealth Magnet version) were the first headphones to make me feel that I didn’t need a dynamic driver for bass tonality and it seems that the Helios can take that same claim for subbass in IEMs. The rumble, articulation, coherency are all just mixed together perfectly for my tastes in subbass.

I can’t finish the subbass section without mentioning “Chameleon”, which is usually a good stress test for an IEM subbass, however, in this case, it is more of a massage for the eardrum, giving a sensation of power that I have not experienced in an IEM before without it becoming overpowering and uncontrolled.

Moving up to the mid bass ranges, the articulation and speed are again there, making any tracks, no matter how busy in the bass areas, sound clean and never seeming to lack any dynamics in the bass area. However, and this is my first negative (which I repeat, is relevant to what I am looking for, not because it is bad), I feel that the midbass is lacking a little bit of warmth and presence to be totally natural on the majority of music that I listen to.

I listen to a lot of acoustic guitars and basses in my music preferences, some samples of which can be found on my test list, such as “Tears in Heaven” by Eric Clapton, “Free Fallin’” by John Mayer or “Seven Nation Army” by Zella Day, just to name a few. With this kind of music I find that the acoustic guitar (and upright bass in something like “Back it Up” by Caro Emerald), lacks a little bit of body to meet my preferences for these instruments.

I know by looking at the graph that the mid bass is slightly below my preferences as far as presence but even with a little bit of EQ in this area, I still don’t find it to be as natural as I would like, which I think could be due to these frequencies being handled by a BA and not a DD. Again, I must stress that this is some very minor nitpicking on my behalf, it is not that the instruments sound totally off, far from it, they just don’t seem to have the body that I love about the midbass of an acoustic guitar or bass.

When listening to similar styles of music that uses electric guitars rather than acoustic, such as “Give Me One Reason” by Tracy Chapman or “Sugar” by Francesco Yates, I do not get this same feeling. I feel that is more relative to the fact that I have been listening to acoustic guitars in a live setting (unamplified) since, well, forever, and it makes it difficult for them to sound the same.

With tracks that move more towards rock, such as “Whole Lotta Love” by Led Zeppelin, then I find the midbass to be great, with great clarity and coherency that makes it possible to even appreciate effects used in dirty tones such as “Bombtrack” by Rage Against The Machine.

Moving out of the bass and into the mids, there is no need to mention the transition as there is absolutely no hint of anything that resembles bleed or bloat. This is obviously helped by that small lack of presence in midbass (in comparison to other sets) but also the fact that these IEMs are so clean and fast that it is not even something to consider.

The mids themselves are very well presented, keeping up with that clarity and speed found throughout the whole of the frequency ranges. Voices are clear and upfront but without becoming harsh or pushing their way too far forwards. From vocals such as Dominque Fils-Aimé on “Strange Fruit”, through to Beth on “Don’t You Worry Child” (who can easily become harsh), I have no complaints about them at all. There is great balance between the male and female vocals on tracks such as “Billie Jean” by the Civil Wars, without either overshadowing the other.

Songs with multiple voices, such as “Hallelujah” by Pentaonix or “These Bones” by The Fairfield Four, are separated perfectly and allow all the layers to be easily identified. I also need to point out that the very deep voice on “These Bones”, which could possibly be affected by the midbass that I mentioned earlier, does not seem to be lacking in warmth at all, which goes to prove even more my point about it being relative to my expectancy of the acoustic guitar rather than the IEMs.

Moving up into the higher regions, I must say that this is by far the best treble I have heard on a set of IEMs. Everything is smooth, articulate, airy, all those words that actually mean nothing but serve to try and explain the sound. There is no issue with sibilance, although it doesn’t tame it either, so if the track is recorded with sibilance, the Helios is not going to hide it. I can see that maybe the treble would be slightly too much (but only slightly) for some people but personally I really can’t pick faults with the treble of the Helios, it is great and, again, by far the best I have heard in an IEM.

The soundstage is also way above the average I have come to expect from IEMs. I mean, it is not an Arya v2 (nothing is really an Arya v2) but it does place itself in the category of being open and spacious, something that is not common on IEMs that I have tried.

Something that helps add to the spaciousness is the detail and placement of images inside the soundstage. This means that it makes the most of the space that is available, placing images in a way that makes it easy to appreciate small changes in placement and making the whole picture seem larger than it actually is. This is by far the most detailed IEM that I have heard also.



I think that I have made it clear that I am very impressed with the sound of the Symphonium Helios, as I have already said a couple of times, it is easily the best sounding IEM I have heard. The details, spaciousness, sound signature, there really isn’t anything that can be called an issue, it is just an amazing set of IEMs.

Now, I guess that thousand euro question is… would I actually spend a thousand euros on the Helios?

Let me say that I am very tempted and just the fact that I am even contemplating spending this kind of money on a set of IEMs is proof that I am really impressed with them.

So, what is stopping me?

Well, apart from the fact that I still feel that 1k is a lot of money for a set of IEMs (it was only a year ago that I thought it was crazy), if I was to spend it, I would want something that is perfect. By this I don’t mean a perfect set of IEMs, I mean something that is perfect for me, and there are really only two things that I don’t find perfect about the Helios for my personal taste.

The first is comfort. While these are not uncomfortable IEMs, they are also not the most comfortable IEMs I have worn. I always notice them in my ears. As I said, I am not a fan of deep insertion and these do go a little deeper than my preference. I can also get a good seal by using tips that sit further away from the shell and they still sound great, but not quite as amazing as when inserted properly. I also find that the back part of the triangle shape rests on my ear and the top sticks out at an angle, causing the cable to be at a weird angle also, which is not terribly uncomfortable but it is something that I notice constantly.

The second thing that has me hesitating is the mid bass / lower mids timbre that I mentioned. With almost all music except for that based on acoustic guitars and basses, this is not even an issue, however, a very large part of my listening is based on music that revolves around these two instruments. Again, this is not bad by any means, far from it, but it is just not the perfection that I would hope to achieve by spending this much on a set of IEMs.

Now, both of those reasons are completely personal. Comfort is a very personal thing and my impression of an acoustic guitar's natural timbre may not coincide with yours. You may not even listen to any music that involves acoustic instruments at all, in which case I would not be able to point out a fault at all as far as sound. I have listened to all kinds of music throughout the week and there really isn’t any genre that I haven’t enjoyed on the Helios. Even music that is based on acoustic guitars has been thoroughly enjoyable, I really am nitpicking when I talk about that “body” of the instrument.

You might even be someone with plenty of disposable income and think that 1000€ is a very reasonable price, which I guess it is in comparison to other IEMs that are twice as expensive, or even 3, 4 or 5 times more expensive. I obviously haven’t heard any of those more expensive models but based on commentary from people that I trust, I don’t think the Helios has anything to worry about as far as sound quality in comparison.

So, I am still on the fence about the purchase but what I am not on the fence about is the fact that they are an amazing set of IEMs that I am very grateful to Symphonium for sending out to me, giving me the opportunity to get to hear them.

As I mentioned at the beginning, I am sending these on to Vertex and Cqtek for them to share their unbiased opinions of these IEMs as, again, I might have already had a preconceived opinion before starting this review, so I would suggest checking out their reviews once they have had chance to publish them.
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