64 Audio tia Fourté - Flagship, Hybrid, Universal IEM Review

64 Audio tia Fourté - Flagship, Hybrid, Universal IEM Review

The tia Fourté, launched almost 18 months ago, and the flagship model in 64 Audio’s IEM line-up, are a four-way, hybrid-driver, design and were the first IEM to introduce both their new “tia” (Tubeless In-ear Audio) drivers with acoustic mixing chambers and their “Apex” pressure-relief technology. The combination of these features is promised to elevate audio quality and comfort beyond the already well-regarded performance of their earlier models.

I originally auditioned the tia Fourté at launch but, despite being initially impressed, held off on pursuing them further as at their price-point I really wanted a custom-fit option; I had resigned myself to waiting for that option. As of today, such a beast still does not exist. And chatting with the 64 Audio reps at CanJam @ RMAF in October this year indicated that while it is something being considered, there’s no timeline in mind nor any guarantee it will ultimately happen. Waiting even longer for something that might never happen ceased to be appealing … so here we are …

The set of tia Fourté that I am reviewing was on kind loan from 64 Audio and was supplied as part of a “demo set” comprising all of their universal models (which I will cover individually in subsequent reviews). As I write, these are all winding (as opposed to “winging”) their way back to 64 Audio HQ - as they’re relatively local.

It is worth nothing that, somewhat uncharacteristically, there is likely a bit more relevant “meat” to what I address in the “Technology” section than normal in my reviews, particularly with regard to the effects of the “Apex” technology and direct comparisons with what it supersedes and competes against - so don’t automatically skip over it if that’s of interest.

Review Equipment & Material

Sources and amps used in this review includes the Chord DAVE, Chord Hugo 2, RME ADI-2 DAC, Sony NW-WM1Z, Questyle QP2R, AudioQuest Dragonfly Red and Apple USB-C to 3.5mm Adapter (via a 2018-model iPad Pro 11”).

Headphones used, for comparison, include the Focal Utopia and Clear and Fostex TH900 Mk2 and IEMs included the 64 Audio tia Trió, U18t and U12t, Empire Ears Zeus XR (Adel), Etymotic ER4-XR andCampfire Audio Andromeda.

The majority of the music I use in my evaluations is in “Red Book” CD format (16 bit, 44.1 kHz), most of which comes from CD rips; an initial playlist for my audition listening can be found here. Where appropriate/referenced I utilize a number of high-quality, high-resolution, albums, needle-drops, and also some native DSD content.


The tia Fourté utilizes two of 64 Audio’s custom “tia” open-faced balanced armature drivers, one each for the highs and midrange, a balanced armature for the high-mids, and a dynamic driver for the bass/lower registers. These are mated with the tia acoustic chambers for mixing/optimization and coupled with the proprietary Apex system to reduce pressure/fatigue and improve stage and openness.

Both the “tia” and “Apex” technologies are featured across the whole range of universal IEMs here, in slightly different forms and configurations.


One of the most interesting features of 64 Audio’s IEMs is their proprietary “Apex” technology. You can delve into the details directly on the Apex technology page, but in essence it’s an interactive pneumatic vent that acts to relieve pressure on the ear-drum and reducing listening fatigue. At the same time it provides a more open and dimensional soundstage, and in the case of models with removable Apex modules, allows some degree of signature and isolation adjustment.

Apex replaces the conceptually similar ADEL technology in that 64 Audio had been using previously (they have a blog-post discussing why they developed their own, in-house, solution - for those that are interested).

Apex vs. ADEL vs. Conventional IEMs:

Apex and ADEL aim to do fundamentally the same thing; however, the mechanisms by which they do this differ – with ADEL using a secondary membrane that moves as air pressure in the enclosed space changes, and with Apex employing a “pneumatically interactive vent” that allows for air/pressure exchange.

In general, both Apex and ADEL systems also result in a somewhat lower degree of isolation than conventional IEMS, which simply seal the ear canal.

IEMs have long given me issues with both physical fatigue (due to comfort/fit issues) as well as listening fatigue. It was with some interest, then, that I first tried the original ADEL-equipped U12 model. That generally addresses both types of fatigue quite nicely, although I always had a suspicion that it was the cause of some lessening in the ability to portray bass texture.

Having both Empire Ears Zeus R (non-ADEL) and Zeus XR (ADEL) on hand at the time, I was able to make a mostly-direct comparison there and, sure enough, the non-ADEL version renders bass with slightly more detail and nuance than the ADEL-equipped version. Though this does come at the cost of a change in the sense of space/stage in the reproduction and results in significantly faster onset of listening fatigue.

The results here made me particularly keen to see how 64 Audio’s new “Apex” modules, which replace the “ADEL” technology they were previously using, stack up in that regard. It did not take much listening to ascertain that bass resolution, texture, and articulation are definitely improved here vs. the “ADEL” solution - and are on par with the best IEM-bass I’ve heard so far. And, at the same time, I find that they remain completely free of listening fatigue.

In general I can’t go more than a couple of hours listening to conventional IEMs without needing a short break – including having to remove them from my ears for a bit (for comfort and to let them “breathe”). With the ADEL-equipped units that goes up to three or four hours. And then with the Apex technology, I was routinely listening for six to eight hours at a stretch with no discomfort or fatigue at all and without having to take breaks or remove the IEMs here and there. And as an added bonus, my ears weren’t getting hot or moist during the longer Apex listening sessions.

That’s a definite, very welcome, change for me.

Most of 64 Audio’s line-up uses swappable Apex modules, which vary both tuning of the sound and the degree of isolation provided by the IEM. The tia Fourté (and the tia Trió) have integrated Apex technology, equivalent to the “m20” module, and as a result do not allow you to switch them around.

For my personal listening, I find that the Apex system does a better job of reducing fatigue, improving comfort and imparts less of a penalty on bass reproduction than ADEL. Even given the slight loss of bass-texture I find with the ADEL system, I’d still take it over a conventional IEM.


The “tia” technology, the full details of which you can also read about on 64 Audio’s technology page, is a combination of proprietary open-faced balanced-armature drivers, acoustic chambers and an integration/mixing design that avoids the use of tubes in delivering the sound from the drivers to the ear - instead employing a single-bore.

Its goal is to reduce/eliminate phase issues, improve coherence, resolution and stage while ensuring a smooth response profile. At a very high level, compared to other flagship IEMs that employ a tubed-design, I would say it is successful and the difference is easy to hear, for the details we’ll have to talk about the sound …


The tia Fourté are an all-metal build that feels very solid, has a high-grade and resilient finish, a surprisingly compact shell (smaller than every other IEM I have, except the ER4-XR). There are very small holes for bass-porting and the Apex vent if you look close enough. Bore size fits the 4mm internal-diameter I tend to have most of my third-party tips in perfectly.

The backs of these IEMs are adorned by an inset, patina-rich copper plate. The appearance of these can vary significantly. Some are mostly blue/black, others have pronounced copper and red-tones in them. They’re not the most visually appealing units in my opinion, perhaps because I like all the options that are available with custom models, but they’re distinctive and the finish is certainly interesting. I find the inserts on the U18t to be more attractive, and those are biased more towards reds/oranges.


64 Audio’s IEMs are supplied in a simple box, in which you’ll find the IEMs themselves, their standard “Pro” cable, which is a two-pin termination on the IEM end and is finished with a sturdy, right-angled, 3.5mm TRS (single-ended) plug on the other.


Three sizes of two different types of tips are supplied, along with a small, hard-sized, carrying box that will hold the IEMs, each in a separate chamber so they can’t clink against each other, the cable, cleaning tool and a small tin of desiccant to remove moisture.

I almost never get on with the tips supplied with any IEM - the triple-flange units that come with the Etyomtic ER4-XR being the only notable exception. This wasn’t any different here. So I pulled out my box of various tips and spent some time swapping them around and finally settled on two different pairs that I found worked well for me.

The SpinFit CP240 (double-flange) tips were my overall preference. They yielded a consistent, solid, seal, remained comfortable for multi-hour listening sessions and didn’t affect the signature of the IEMs as much as the others I tried.

The other option that worked well for me was the Comply Comfort TSX line (comfort-shape with integrated wax-guards). These attenuated the treble a little, which may well be desirable for some listeners, but took a little definition and impact from the bass.


First Impressions and Surprises

Right from the first notes it was apparent that I was listening to something different with the tia Fourté. Different enough that my initial listening session was both interesting also rather disorienting. It was immediately clear that they are extremely resolving - they are the most resolving and detailed IEMs I’ve heard, in fact (true when I first heard them, and still true today). And they exhibit superlative layering and separation. And it is here that the first day, or certainly the first several hours or so, proved to be so … interesting.

How so?

The entire mix is laid completely bare. The combination of extreme resolution and separation means it is trivially easy to hear individual instruments, themes, sounds, and the initial effect was as if I was continuously shifting focus between each of these individual elements. The result of that was that I was not experiencing the music itself as a cohesive whole and was, instead, listening to, and focusing on, the individual elements.

Coherence has been a big issue for me with hybrid IEMs, and also multi-driver headphones, and the first IEM I’d heard that didn’t have such issues was the AAW W900, so this was a real concern even before I’d heard the new 64 Audio unit.

After several hours of listening this effect went away and I began experiencing the music as a fully coherent, yet still beautiful detailed and delineated whole. I could still focus and pick out any individual element with incredible ease, but I was no longer doing so constantly and subconsciously. And from that point on it I had no further issues with hearing the whole performance or getting inadvertently distracted by specific elements of it.

Now, it is, perhaps, tempting to attribute such changes in the listening experience to “burn in”. In this case it is easy to state that what I experienced is categorically not a case of burn-in with the IEM. I know this, as a) my initial experience was with a pair of tia Fourté that already had a fair number of hours on them AND b) because when I received a new set, I had no issues with coherence there right from the first listen.

This presents something of a potential challenge when it comes to auditions. A few minutes at a meet or show might not be enough to adjust to what is, for me, a new level of presentation. I’ve talked with other owners and reviewers and I am not the only one that had this experience. My initial reaction to the tia Fourté, while being very impressed, was difficult to reconcile musically and I am glad I had the opportunity to listen for several hours that first time, otherwise I could have come away with impressions that didn’t endure and weren’t a complete picture of what the tia Fourté experience really is.

Signature & Tonality

The tia Fourté are not a neutral transducer. At all. 64 Audio include a little bar-graph/equalizer style graphic on the product pages that shows the relative “tuning” for each of their IEMs. This is rather coarse - and while it correctly indicates that the bass and treble of the tia Fourté are elevated vs. neutral it doesn’t really accurately convey by how much.

Bass is emphasized, not quite to bass-head levels, but enough to be immediately noticeable. And there is a lot of treble energy. Enough to satisfy treble-heads. Enough that they could be considered bright - where it not for that bass. The net result of which is a tilted U-shaped signature, with the greater emphasis on the higher registers. So if it’s neutral you want, either look elsewhere in 64 Audio’s line-up (e.g. the U18t), make sure you have a good EQ option, or look at other options all together (my neutral reference IEM is currently the Empire Ears Zeus XR Adel in “R” mode).

Detail & Resolution

Across the entire spectrum, these are the most resolving and detailed IEMs I’ve ever heard. It’s like listening with the musical equivalent of a scanning/tunneling electron-microscope. No detail, no matter how small, escapes - it is all rendered in sharp relief, perfect focus and with absolute clarity. The more complex the recording or performance, the more the tia Fourté demonstrates its ability to resolve fine detail without ever getting congested or confused.

As such, 64 Audio’s flagship is at its best paired with highly-resolving sources and quality source material. While it’ll sound great from streaming sources, even straight out of an iPhone or iPad with Apple’s 3.5mm dongles, it really pays dividends to pair it up with lossless source material and a more capable player. I set them up using a Sony NW-WM1Z as a transport feeding a Chord Hugo 2 and when driving the tia Fourté this represents the highest-end, portable, in-ear listening system I can think of - and definitely the most capable combination of such components that I actually own.

In a setup like this, listening to some early Prince work, and paying proper attention, resolution is such that you can hear what seem to be individual edit “punch” points from the (tape) master.

Transducers with elevated treble levels often sound more detailed than they really are. Turning the treble levels down using a high-quality EQ solution (DMG’s Equilibrium) did not result in any less realized or apparent detail. Everything I could hear before was still present, and is not being artificially added due to treble-effects by the IEM itself.


Ever since I heard the Campfire Audio Vega and the AAW W900, I’ve found the bass performance of balanced-armatures to be a bit lacking. Certainly, some of them have lots of bass, and play suitably deep, but it’s just not as satisfying. For me, good dynamic drivers, either as the sole transducer, or in hybrid configurations like the tia Fourté, deliver a much more convincing bottom-end.

And I’d have to say the 64 Audio unit has an excellent dynamic driver - as the bass hits you like the proverbial freight train with almost visceral slam and impact. Yet it remains punchy, taut, and fast, is well textured and highly articulate with solid sub-bass rumble and growl more akin to that of a good closed-back headphone. In terms of bass quality, these are my favorite IEM so far.

The bass quantity is definitely quite elevated here - I suspect only the bassiest-of-bassheads will be left wanting. But that’s about the only thing about it I can find “fault” with on the bottom-end. Otherwise it provides a truly solid musical foundation, maintains excellent drive, and bops along happily and under excellent control no matter how complex or tuneful the lowest registers become - it’s definitely not a one-note presentation.


The midrange here, while clean, smooth, and very balanced in itself … is a bit overpowered by the bass and treble. They don’t intrude into it as such, so there’s no muddying from the upper-bass registers, nor smearing of lower-treble - it remains extremely clean but it is subdued compared to the levels of either extreme. To really see what’s possible here, you want to bring up the mid-levels a bit (or better still, lower the bass and treble levels some). And when you do, the amount of audible detail that is revealed is nothing short of amazing. You can certainly hear the excellent midrange detail when used natively, it’s just less overt.


I find the treble delivery, while rather prominent, to be very smooth. I’d stop shy of calling it “hot” (which is the term I ‘d use if it was leading to fatigue), and I found no added sibilance in my listening, even with trickier female vocals. There is just quite a bit of it. Treble energy that is. Were it not for the bass levels exhibited here, I’d have to lean towards labeling these as “bright”. As it is they do stay shy of that, but you’re still getting a treble-tilted U-shaped result.

This is accompanied by an extremely spacious and open sound, with a very natural sense of air and suitable and delicate sparkle. I’ve only heard this natural and expansive a sense of space in IEMs that are using either Apex or ADEL systems or that are actually open-backed (e.g. the Audeze “IEMs”). Almost everything else sounds almost closed-in by comparison.

Other than the elevated level, the actual treble delivery renders cymbals like cymbals with them sounding suitably brassy when brushed or hit, brass in general, and when played aggressively/discordantly, carries excellent bite without becoming artificially sharp or harsh.

Separation, Layering & Stage

As good as it gets in an IEM, and better than most full-size cans. It is easy to pick out any point in a performance, spatially, instrumentally or vocally and focus on it - with it clearly “drawn” and present. First vs. second row, complex layered vocals, heavily tracked mixes are all easy to unfold and hear deeply into.

Stage is expansive with excellent lateral positioning and an uncanny sense of depth. Binaural recordings are particularly vivid in their imagery. And the general sense of space and openness in a venue is portrayed in a manner in which you can almost “sense” it beyond just what you can actually hear. One of my favorite albums for experiencing this is the Cowboy Junkies’ “Trinity Session” (a stereo recording done using single-ambisonic microphone). IEM-wise, I’ve only heard this rivaled with other Apex and ADEL equipped IEMs … stage-wise this is the Sennheiser HD800 of the IEM world.

Dynamics & Transients

They’re fast and impactful with major shifts in musical content, perhaps the IEM-equivalent of the higher-end Focal models in this regard, and able to track and portray very subtle inflections and changes in the bowing of a violin, the wavering of breath in horns and woodwind instruments, and especially in a performer’s voice. Micro-dynamics, in particular, are state-of-the-art, rivaling Focal’s Utopia or the 8XX series Sennheisers on a high-end tube-amp. And there is an unmistakable deftness to the way they handle rapid staccato components in the music. No matter how much is going on, they remain composed and revealing.

Whether it is down to the open-nature of the unique “tia” drivers, or the tubeless design, or some other factor, transient response is also exceptional. My favorite exemplar - plucked-strings having amazing attack, as does percussion - electronic or with real instruments. There’s no overhang on notes that isn’t supposed to be there, and the leading edges of notes are clean and crisp.


The “Apex” system means that isolation is going to be lower than with a fully-sealed IEM. Measured isolation, or more accurately how much outside sounds are attenuated, is at -20 dB. That’s enough to listen at moderate volumes on a commercial aircraft without the cabin noise intruding on the music, but not enough to shut it out entirely when nothing is playing or in very quiet passages (for that, you’ll need something like the Etyomtic ER4 series, with triple-flange tips - and their accompanying issues with comfort and deep insertion requirements).

Quick Comparisons

Some specific comparisons to some of the IEMs I have on hand at the moment, both from my own personal collection and the 64 Audio demo-set.

vs. Etymotic ER4-XR

The ER4-XR, once sealed properly, give an entirely coherent delivery - as one would expect with a single-driver design. Isolation, with the triple-flange tips, is as good as it gets with universal fit IEMs. Signature is almost entirely neutral, with a modest, deliberate, raise in bass levels - as you would expect with the XR (eXtended Response) version.

The SR (Standard Response) version is closer to the original tuning of the ER4-S, which I owned and used for more than twenty years, but was something that I always wanted just a “bit” more low-end oomph from. Neither the SR or XR versions are any competition for the way the Fourté handles the bottom octave.

Comfort here is not great. To get good isolation you need the triple-flange tips, and those require deep insertion which can become irritating very quickly. And pressure builds up on the ear rapidly too - vs. the non-existent sense of pressure that comes with the tia Fourté.

Back to back these sound somewhat dull compared to the Fourté - lacking both treble-extension and any sense of air. The natural edge comes off harsher instruments and voices somewhat. Stage is significantly compressed and two-dimensional. Detail is good, but not in the same class as the Fourté nor the other options covered here.

vs. Campfire Audio Andromeda

Getting the best out of the Andromeda requires a very quiet source, as they seem unusually prone to hiss, and ideally an output impedance of about 2 ohms. A lower OI will result in a bass-wards tonal shift which gets quite prominent by the time you’re down under half an ohm. Otherwise, these are essentially tonally neutral.

Using something like iEMatch inline with the Andromeda largely addresses both the hiss and the tonal shift issues.

Resolution and detail here are excellent, if not quite on the same level as the Fourté. Dynamics also favor the Fourté, something easily noted with micro-dynamic fluctuations in vocals and bowed strings. Treble has good extension, air and sparkle. Mids are present and pure. Bass is a bigger shortfall - certainly good, and not just “good for being balanced-armature”, but not in contention with the dynamic-drivers used by 64 Audio, nor, indeed, in comparison to Campfire’s own dynamic and hybrid models.

Bang-for-the-buck here is very high - maybe as good as value gets for high-end IEMs.

Comfort, for me, is a problem though. The nozzles are just too large for my ears, and no tip-pairing I’be been able to try lets me have them both comfortable and still get a proper seal.

vs. Empire Ears Zeus XR (Adel)

The Zeus remains the most neutral IEM I’ve heard (in its “R” mode). It doesn’t quite match the detail levels attained by the tia Fourté, particularly in the upper-mids and treble, but still gives an excellent showing. The 64 Audio unit leaves the Zeus in the dust on bass performance, however - not just in terms of quantity and slam, but also for detail and texture.

You can improve the bass texture some by using the adjustable “MAMS” Adel module with the Zeus, and closing it down all the way. But this results in losing the fatigue-relieving behavior of that system, and also results in a more closed-in, and less airy, rendering.

Otherwise, the Zeus are closer to the U18t than they are the tia Fourté.

vs. tia Trió, U18t and U12t

Since I will be posting full reviews of these IEMs in the near future, including a detailed all-up comparison, I am going to limit my comments here to some obvious differences.

In short, while excellent for “balanced-armature bass”, both the U18t and U12t fall short of the articulation, texture and impact of that delivered by the tia Fourté and it’s dynamic bass driver. Though the U12t does offer an even more pronounced bottom-end, relatively speaking, than the flagship.

The U18t is clearly the “reference” tuning here … being similarly neutral to the Zeus XR (in “R” mode). It is only the bottom-end that lacks compared to the tia Fourté. Detail levels are very close, and it is a bit easier to hear that in the mids when run natively with the U18t.

Both the U18t and U12t will let you adjust the bass-levels modestly by switching between the m20 and m15 Apex modules, something not available on the Trió or Fourté due to their integrated Apex system.

The tia Trió can be thought of as a tia Fourté with a bit more apparent/relative bass-presence or, alternatively, a rather less treble energy. Actual bass-level is about the same, but in relation to the overall signature comes across are bit more prominently. This is probably a better option if you are treble sensitive or just prefer a bassier presentation. Mids are a sliver more evident here as well.

All of these models exhibit a similar sense of openness and space, with a broader stage then any fully sealed IEM I’ve heard.

Comfort is excellent across the line-up, with fatigue essentially absent even over protracted (8 hour-ish) listening sessions. Nothing to split the pack here.


The tia Fourté are an interesting IEM - essentially state-of-the-art in terms of resolution/detail, separation, layering and bass delivery, but with a very definite non-neutral (tilted U-shaped or “fun”) signature. If you like that kind of sound profile, can deal with a bit less isolation than you get with conventional IEMs and, of course, can get past the very high asking price, these are an impressive, entertaining, non-fatiguing, listen.

Even if their native signature is not your thing, if you use, or are willing to use, EQ as part of your listening it is very easy to dial them in to a neutral delivery (hint: dial down the treble and the bass, rather than dialing up the mids) - at which point their other technicalities become hard to beat.

I have a personal, latent, bias - or expectation - that flagship transducers are going to be tuned to be as perceptually neutral as possible - so I am typically rather surprised when that is not the case - which was apparent with the tia Fourté (the Empire Ears Legend X caught me off guard in a similar fashion).

If you seek innate neutrality (i.e. without EQ), then you’ll want to look elsewhere.

Similarly, if you’re treble-sensitive these are unlikely to be what you’re looking for - absent some EQ.

Personally, after several encounters with them, including this most recent, more-extended, opportunity to listen, I’ve come to find the highly dynamic, superlatively detailed delivery, impressive and powerful bass, expansive stage and very open sound, to be both very involving musically and wh

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