64 Audio U12t Universal IEM Review and Comparison

64 Audio U12t Universal IEM Review and Comparison

Review written by Anthony Nguyen (@Antdroid)


64 Audio is a custom in-ear monitor boutique company located in nearby (to me) Vancouver, WA. They’ve built their brand around custom monitors for professionals, but also dabble in the audiophile market with various models throughout the years. This review will cover the $1999 U12t universal monitor, which is part of their audiophile line.

This IEM was sent to me on loan by Taron of Headphones.com. They are an authorized retailer of 64 Audio and you can find this IEM and other great headphone gear on their website! I’d like to also thank the Headphones Community forum and the Headphones Community Preview program for allowing loaner units sent out to community members!


The U12t is a 12-balanced armature monitor that is part of their Tia line. It has 1 Tia high, 1 high-mid, 6 mids, and 4 low BA drivers per side. The tubeless Tia design also features the 64 Audio Apex and LID technologies. The Apex tech allows pressure relief through swappable modules that reduces air pressure during usage, with some slight changes in tuning depending on the module. The LID is 64’s linear impedance design, which allows the IEM to sound similarly regardless of the source impedance.

To test this LID technology out, I used my IEC-711-style coupler to measure the frequency response of the U12t with a near zero ohm output impedance source and then placed a 75 ohm impedance adapter between the source and the IEM cable and re-measured the FR. As expected, the measured response barely changed at all, so the LID technology works! I re-ran the same test with a couple other multi-BA IEMs in my staple (qdc Anole VX and Hidition Viento-R), and they all had significantly varying frequency response measurements at the two impedance values.

 Accessories & Comfort

The U12t comes in a rather large box for how small the IEMs are. Within the packaging are the two sides of the IEM, a black 2-pin cable, various tips, 2 Apex Modules (M15 and M20), cleaning brush, clip, and a plastic carrying case with slots of each item. I wasn’t a big fan of the included cable, as it’s not the most ergonomic and easy to use, nor was I a fan of the case. It’s quite utilitarian in that it has slots for everything include the module and cable tie posts, but I found it to look and feel quite mediocre and rather unfashionable, especially compared to the cases that come with other IEMs which are fabric, leather, or jewelry-style boxes.

The IEM has a teardrop-like shape and rather simple contours; however, the fit is very comfortable in my smaller and sometimes finicky ears. I had no issues putting them on and wearing them for hours. I chose to use Spinfit CP100 (small) tips with this IEM as I found it was the best pairing for fit and seal, as well as sound.


The U12t has a U-shaped sound signature with heavily boosted sub-bass, a flat-tuned mid-range and a moderate pinna compensation in the upper-midrange and treble, and a rather soft and smooth treble range, at least to my ears and using the M15 gray module. Using the M20 silver module increases bass and reduces treble slightly.

Bass is actually presented very close to how I would like it to preferentially. Sub-bass is elevated while mid-bass is tamed down and closer in-line with the mid-range. Many people talk about how the U12t’s bass is good “for BAs” but I think the bass extends extremely well and has a natural decay level in most cases. It defines textures pretty well, though it does fall behind the best dynamic drivers in this category, but there’s no lack of slam, and sub-bass rumble here. In fact, I find it can be a little overbearing at times in songs where I don’t necessarily want so much low-end boom. I don’t necessarily think it’s bloated, but for certain types of music, I prefer a crispy definition, but the low end can over-power some other areas. This is specifically to some acoustic/classical genres, where a very deep and powerful bass or drum line can sometimes overshadow other instruments.

On most tracks, the mid-range is coherent and well-rounded. Since there’s no real dip in the mid-range, which is a preference of mine, I find that male and female vocals are played in-line with one another. Details in this area are showcased well, and instruments sound generally natural.

The upper frequency on the U12t is a little tame, and in this case, I find it lacks a bit of energy for some instruments. Female vocals don’t pop like they do on other IEMs with bigger pinna gain and treble boost, and some instruments like the crashes of cymbals and resonating plucks of strings don’t come off with as much zing and wow as I occasionally prefer. The treble brings the general tonality down to a very, very smooth presentation, that still retains clarity and high levels of resolution, which gives this IEM a very enjoyable experience for all music, and even let’s poor recordings shine a bit more than you’d see on other IEMs with more elevated treble responses.

Fatigue is never an issue with this IEM due to this, which is great, because the combination of the clean, comfort and the enjoyable, resolving listen, makes this a really great choice for those who just want to pop-in IEMs and not have to worry about anything.

I found the soundstage to be slightly above average for IEMs, with more depth than actual width compared to most IEMs. It’s not as wide as something like the Sony IER-Z1R and not as deep as the qdc Anole VX or Campfire Solaris, but there’s no worry of clogged up congestion or claustrophobia. Instrument separation is pretty good as well, which contributes to my previous statements.


In my short-time with the 64 Audio U12t, I’ve been asked how it compares to some of the other flagships. While I don’t have many of the ones I’ve heard in the past on hand, I have heard or owned many and can easily say that the U12t is among my favorites, and is a rather easy choice for a recommended all-arounder that can probably suit most users and most genres of music. That said, it doesn’t necessarily out-shine any IEM in any specific category.

It’s bass response, resolution, natural decay, and texturing and just general microdynamics, is really good, but it doesn’t top the Sony IER-Z1R as mentioned before.

In terms of general overall coherency, I don’t think the U12t outshines the Hidition Viento, as that one just sounds buttery smooth with out any sense of disjointed sound or significant timbre issues, though I do find some issues with it, I’ll talk about in its own review.

In pure resolution and detail resolution, the Shure KSE1200/1500 tops them all, and even for a multi-BA IEM, I still find the qdc Anole VX edging the U12t out with the Viento also in the same level.

And while fit is extremely comfortable, and this is a rather personal thing, I find the qdc shell design is outstanding for fit, size, weight and long-lasting comfort.

qdc Anole VX

When comparing this with the qdc Anole VX, I find they have some similarities as they’re both somewhat U-shaped IEMs. They both have rises in bass, a small dip in the mid-range and what I consider a good amount of pinna gain in the upper-midrange/lower treble and a small amount of treble extension. The U12t has more extended and bigger sub-bass performance, and you feel it with the lengthy rumbling decay, while the Anole VX isn’t exactly shy there either, but it is tamer, and more mid-bass focused with a little more more slam.

I found the VX to also have a little bit of warmer mid-range compared to the U12t, however I found the natural timbre of the U12t to be more correct in this area. The VX treble can be a tad hot at times, depending on the track, while the U12t is much smoother and toned down in the upper frequencies, and can reduce the energy and excitement factor in comparison.

Hidition Viento

With respect to the Viento Reference Universal, which is the switched model of the Korean reference in-ear, I found the U12t to have a bigger feeling bass region compared to the Viento-B tuning, which I believe is the closest matching to the U12t’s total sound. That said, they don’t really match a great deal. The VIento-B is more agile and coherent through the mids with a really nice signature that never feels totally disjointed ever. It is a tad shouty and can be sometimes sibilant, at least in the universal fit, but this is only a problem with bad recorded pop music. The Viento’s pinna boost is much larger than the U12t and also has a more elevated treble range, though also has similar extension capabilities.


The U12t is a really solid all-arounder and worthy of a lot of the praises I’ve read and heard about in the community and from other reviewers. While I don’t think it naturally beats out any specific IEM on the market in a specific topic, it performs near the top echelons of each category of the in-ears I’ve tried and that’s pretty good company to be in. I find it’s one of the easier IEMs to recommend for most all music types and can easily be a default option for anyone looking to start somewhere in the top tier bracket.

- Anthony Nguyen (@Antdroid)


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