Symphonium Helios

General Information

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

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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.


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