It’s no secret that the 64 Audio U12t is one of my favorite IEMs. I fondly recall demoing it half a year ago and being absolutely floored with what I heard. In the span of mere minutes, I simply knew I had to own one, so I immediately jumped on the opportunity when a local friend decided to sell his. I’ve put hundreds of hours of ear time onto my U12t since; it remains a staple of my relatively small IEM collection.
And this is for good reason: While the U12t might not enjoy the hype that follows some of its flagship peers, it’s a prime example of when a company puts everything they have into a product, when said product challenges their own, antecedent products on the playing field, and when the whole is greater than the sum of its parts. Everyone has an IEM they can’t stop talking about - this is mine.
Source and Driveability
All critical listening was done off of an iBasso DX160 (volume ~10-20 on low gain) using lossless FLAC files, Spinfit CP145 eartips, and a standard, 0.78mm pin cable. Because of 64 Audio’s LID (linear-impedance) technology, you should be able to run the U12t off of any source; it’s not picky. My genres of preference include the following: K-Pop/J-Pop, Country music, EDM, and instrumental scores.
64 Audio includes the following accessories with the U12t:
- 64 Audio Personalized Protective Case
- Cleaning Tool
- Shirt Clip
- TrueFidelity Ear Tips (S,M,L)
- Silicone Ear Tips (S,M,L)
Let’s just put it this way: You’re not buying a 64 Audio IEM for the accessories or unboxing experience. Neither of them is particularly enamoring, nor befitting of a flagship IEM in this reviewer’s opinion. The included “premium” stock cable - oh man. Janky memory wire, non-recessed connectors, and with cheap, rough tactile feedback. The case doesn’t fare much better. It forces you to store the IEMs in a very specific way which, aside from being frustrating, puts stress on the supposedly “loose-by-design” connector joints. Have we also talked about the eartips? Wow, do they scream off-brand. No thanks. Do yourself a favor and plan to pick up another cable and case. Oh yeah, just so we’re clear, this is all this coming from someone who actually paid for and owns a couple of 64 Audio IEMs.
The U12t itself is pretty sweet at least. It has a teardrop-shaped housing, and it’s one of the most comfortable IEMs I’ve worn. I can wear it for 5+ hours straight which simply doesn’t happen for me with other IEMs. Of course, fit is 100% subjective and all that good stuff, but it doesn’t hurt that the 64 Audio IEMs feature the company’s proprietary Apex technology. You’ve probably noticed that your ears get fatigued listening to your IEMs for longer periods. Part of that might just have to do with the fit, but it’s also because those sound waves are putting pressure on your ear drums. The Apex technology helps release this pressure, allowing you to listen longer. Seriously - while it might seem like a gimmick, once you try Apex it’s hard to go back.
Frequency response taken off of an IEC-711 coupler. Measurements are raw and matched at 1kHz. Anything after 8kHz should not be considered accurate given coupler resonance.
Above you can see measurements of the U12t using the various Apex modules. All you really need to know sound-wise is that they affect the bass. The M15 and M20 modules will give you a pronounced sub-bass shelf (with slightly more quantity in the M20’s case) while the MX module (not included) will completely attenuate said shelf. The overall tonality of the U12t is something of a U-shape. If you want the low-down, it goes something like “slick, resolving” and to take a note out of my fellow reviewer Resolve’s book, “with a bit of flare up top”. Really, most any genre flies well with the U12t, and while it’s certainly not neutral, if that’s more your jam then you can always purchase an MX module too.
I still remember the first time newbie-me heard the U12t’s bass, and...frankly, I wasn’t too impressed. The U12t neither slams as hard, nor does it have the same, meaty transient density that some of the top-tier dynamic driver IEMs exhibit. It doesn’t help that there’s also a slight plastickiness to its transients. But as my understanding of what qualifies a good bass response has developed (or more accurately, I’ve realized I dislike most every other BA bass response I’ve heard), my appreciation for the U12t’s low-end has grown considerably.
Starting with the frequency response itself, there is a strong sub-bass emphasis that levels off oh-so-perfectly at 200hZ, never bleeding or remotely entering the midrange. This is perfect for my tastes, as I find too much mid-bass has a tendency to delve into bloat. Intangibly, bass texturing is present in moderation, as is decay, and the U12t maintains a lot of the more desirable characteristics that come with a BA setup: namely speed and nuance. I do find swapping in the M20 detracts marginally from transient attack, but it’s a trade-off I don’t mind for some extra “oomph” in my bass. And make no mistake: The U12t has some of the finest BA bass there is; it can be forgiven for falling short on some of the aforementioned intangibles.
Midrange tonality is dead-balanced in terms of note-weight, with the ear compensation peaking comfortably at around 2kHz, right in line with my preferences. This is easily one of the safest midranges I’ve heard. There’s nothing, barring preference, that I would consider an outright deal breaker. And indeed, while sibilance is a complete non-issue, I’d look elsewhere if you prefer a more in-your-face tuning, as the U12t’s midrange can sound slightly recessed by comparison. This extends to guitars and stringed instruments which don’t carry quite enough body for my tastes sans having a crisp, dainty quality to them. A small niggle it is, though, and I absolutely adore the upper-midrange dip from ~2-5kHz. This is similar to the dip that the Andromeda 2020, an IEM I’d consider to have excellent imaging, exhibits. Tuning trick or not, the dip works wonders for center image diffusal; that is, making it feel like the vocalist is actually performing there in front of you.
Okay, we definitely need to talk about the treble. 64 Audio is known for their use of the “tia” supertweeter, an unlidded BA driver mounted directly to the inside of the IEM’s nozzle. Instead of routing the high frequencies through a tube, they’re fired directly into your ear, thus bypassing ancillary frequencies. Sounds pretty cool on paper, right? But the way this translates to practice is surprising. To this end, the U12t actually has something of a mid-treble suckout from ~8-10kHz. This is what most people are citing when they say that the U12t’s treble is more laidback or inoffensive.
Personally, I’m not a fan of this type of dip, as it lends cymbals to a certain hollowness, but the U12t also peaks strongly for air at around ~16kHz. Mind you, this is a frequency at which some listeners might struggle to hear it, and as a result, the impressions I’ve read online seem to vary wildly. In my instance, what I hear is indeed a more laidback treble response, but with copious amounts of microdetail and pseudo-air up top. It’s really quite unique - albeit not particularly natural - in that upper-frequency instruments don’t necessarily hit with exceptional stick impact or sparkle, but rather have a glistening, ethereal quality to their decay.
This sort of exquisiteness to the treble also serves to advance the U12t’s imaging capability. For a sense of staging, the U12t is fairly average in the width and height department, but has excellent perceived depth with the closest to a speaker-like center image that I have heard in an IEM. This is likely a combination between the relaxed pinna compensation, upper-midrange recession, and the unique treble reverb. It's truly uncanny and, intended by 64 Audio or not, distinctive to me of what the right synergy between tuning and intangibles can pull-off. And those positional cues, oh my. This is a subset of imaging that, for me, refers to the extent with which one can discern where individual sounds are coming from on the stage. The U12t excels at this metric. In Sawano Hiroyuki’s “Cry,” I can easily pinpoint the drummer smacking away at the far back of the stage behind the vocalist appropriately, the vocal overdubs coming in from the back exactly where they should be, and the strumming of the guitar and cymbal crashes alternating from the left and right - all of this simultaneously.
Along these lines, the U12t is also quite resolving. I don’t think its resolution, specifically, is top-tier for reasons I’ll outline below, but for a sense of innate detail, layering, and the ability to capture the image, the U12t can certainly play with the best. Something else interesting about the U12t is that it largely manages to circumvent the dreaded “BA” timbre, a sort of weightlessness or metallic smearing to notes. Again, I’ll delve more into how it does so below - which isn’t without consequence - but know that the trait doesn’t present itself very strongly. It’s more akin to a light blanket over the timbre, a slightly warm one at that. While calling it natural would be a stretch, it’s almost reminiscent of the more musical, timbral coloration I enjoy in moderation. There’s just something really satisfying about how this all meshes together; some have described the U12t’s presentation as “analog,” and perhaps that’s the word I’m looking for.
But of course, I’m not done talking up my favorite IEM. And in the spirit of subverting expectations one last time, the U12t excels at the pitfall of many a BA IEM: macrodynamics. For those who may not be familiar with this term, it refers to the decibel gradations (quiet-to-loud sections and vice versa) that are present in a given recording, and an IEM’s ability to replicate them. While most BA IEMs have a tendency to sound “flat” or compressed, failing to scale these shifts appropriately, the U12t is startlingly dynamic. From the abrupt, thunderous transitions of Sawano’s “e of s” to capturing the shift in energy from the synth effect to the baseline at 1:20 in Taeyeon's "Make Me Love You," the U12t carries itself with decided ease. I can’t speak for everything that’s out there, of course, but I can say that I haven’t heard another BA IEM that matches the U12t in this respect, and I’ve heard plenty of the top-tier stuff.
Oh, boy. Critiquing the U12t is no easy task, especially given that it walks the line between being conservative and being just the right amount of engaging for my tastes. That being said, let’s talk about the double-edged sword that is the U12t’s transient smoothing.
You might be wondering, “What is transient smoothing? Heck, what are transients even? This guy might as well be speaking in another language!”. And yeah, that’s definitely a good question. Transients are composed of 1) the attack and 2) the decay function. The attack is the sharpness with which notes are articulated, and the decay is the length of time with which they are drawn out - collectively, they are what people generally refer to as a transducer’s “speed”. A quicker attack is almost always a good thing, whereas decay is more subjective, particularly when it comes to bass.
In the U12t’s case, the transients are articulated towards the middle in terms of speed and without egregious overlap; however, they take something of a “rounded” edge or softness. All the 64 Audio IEMs I’ve heard exhibit this trait to a degree, and it’s likely a product of the company’s unique BA drivers. This comes with its own set of consequences, though, which I’ll outline here:
- Resolution, the clarity with which notes are articulated, takes a hit. Against other heavy-hitters like the Empire Ears Odin, qdc Anole VX, and even Sony IER-Z1R, the U12t is fighting a losing battle in terms of this metric.
- Given said softness, some might find the U12t lacking in that magic, “X” factor. If you can’t quite hear the ~16kHz treble peak to top it off, I can definitely see why some have found the U12t too boring. And that’s fine (wait, no, it’s not), different strokes for different folks.
Another dealbreaker I can think of is if you do have particularly sensitive hearing. The ~16kHz treble peak can be fatiguing if you’re not used to that much air. You can neuter this by swapping eartips, though. Heck, I thought the U12t was a darker IEM until I swapped out the Final Type E tips (which kill the highs a good deal) I originally used!
It might come to your attention that none of these traits is an outright dealbreaker. And regarding the transient smoothing specifically, it’s a good part of the reason why the U12t is so easy on the ears and coherent. However, I recognize that not everyone will perceive these traits the same way I do, so as always I think it’s fair to point out what could be a dealbreaker.
Sony IER-Z1R ($1699)
There is exactly one IEM that I can confidently say I’ve enjoyed as much as the U12t, or that I think is a fitting equal: the venerable Sony IER-Z1R, the de-facto king of hybrids and bass.
The IER-Z1R follows a more V-shaped tuning, and its bass is hands-down the best bass response in an IEM there is. The bass transients are nothing short of incredibly dense and meaty even for a dynamic driver, and it’s responsible for my frequent distinction of “for a BA” when describing the U12t’s bass. The IER-Z1R has something of a lower-midrange suckout that’s unpleasantly gritty at times, followed by a rise to the upper-midrange that I also find contentious. Its treble is characterized by heavy amounts of lower-treble impact and terrific reverb, much more than the U12t’s. It stands that the U12t is the better-tuned, safer IEM in this reviewer’s opinion.
Intangibly, though, the IER-Z1R is something special. While it’s eclipsed by the U12t in terms of detail retrieval, the IER-Z1R’s sheer resolution is incredibly good, especially given that its transient attack seems skewed to the slower side of things. And if the U12t’s calling card is its impressive dynamic range, the IER-Z1R’s would be its staging capabilities. It’s stage distribution is unabashedly sonic-wall free with exceptional height, and the result is a larger-than-life presentation that...well, simply makes you feel like a king.
While I'm more of a U12t boi these days, there's nothing quite like the IER-Z1R. The only problem? I can’t listen to it for more than an hour at a time! The IER-Z1R’s fit is atrocious, and as such, I struggle to confidently recommend it without a solid demo session.
At its worst, the U12t is an IEM that many would be forced to admit is “objectively” good. And really, that’s the U12t’s strength: It’s the student that gets 90% in every subject, but can’t seem to get 100% in anything. And you know what? That’s exactly how I like it. Audio is characterized by a series of compromises; the U12t is just the IEM that makes the least amount of them to my ears. There’s security and confidence to be had in knowing that you have an IEM that can handle everything you can throw at it. So if you’re looking for one of the most well-rounded flagships on the market, or heck, you simply don’t know what you want out of an IEM, the U12t would be my top recommendation.