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 @ Head-Fi, 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.

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

Build and Accessories:

Symphonium Helios packaging
  • 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.

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.
ThieAudio Monarch Frequency response - Can be seen from the Frequency Response Index

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:

Symphonium Helios 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:

Symphonium Helios 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:

Symphonium Helios prediction EQ with 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.

Bewarned: 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):

Symphonium Helios prediction EQ with Bass EQ
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.

Hell, 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.

Recommendation ratings: Recommended