64 Audio’s been on something of a hot streak lately, having released the Nio, the U18s, and now the U6t. What might surprise some readers, however, is that, at least sonically, both the Nio and the U6t are older IEMs. They’ve actually been in circulation for years as the universal demo units of 64 Audio’s N8 and A6t IEMs respectively. But of course, that’s not stopping me from looking forward to some good ‘ol 64 Audio IEM hype.
And right, about that: the day the U6t arrived, I spent the entire afternoon and night listening to it. Then I spent all of day two listening to it. Then all of day three. Then...you know what? You get the idea. I spent an entire week listening to pretty much just the U6t, only swapping to other IEMs for A/B, or to listen to my trusty speakers. I don’t know about you, but for someone like myself who is constantly swapping through transducers, that never happens. Let’s take a more in-depth look at what has my ears glued to this IEM and what the newest point of entry to 64 Audio’s universal lineup is packing.
Source & Drivability
All critical listening was done with the stock cable, Spinfit CP145 eartips, and my iBasso DX300 and iPhone X using lossless files. The U6t is an easy IEM to drive, and you should experience no trouble running it off of any sources. Thanks to 64 Audio’s LID (linear impedance) technology, the U6t also has a fairly flat impedance curve; its frequency response won’t change depending on your source.
Per usual, I’d recommend just swapping the stock cable - wait, hold a moment. Something is different here. 64 Audio has finally listened to their customers’ pleas, and we have a bona fide, legitimately usable cable! Gone are the painfully annoying memory wire and the sand-papery texture to the cable. It’s still not the best stock cable I’ve seen, but this is definitely a major step forward. Aside from that, 64 Audio has also begun including a number of SpinFit silicon tips and their new leather case with their IEMs.
Moving to the U6t itself, it has a matte, slick look. Its faceplate is clearly inspired by the 64 Audio Nio’s, with an aluminum chip covered by an epoxy-domed cover. The milled-aluminum shells have also been blasted grey; running through the body of the shells, you have a cylinder slot for the Apex modules.
For readers not familiar with the Apex technology, this is 64 Audio’s simple but clever solution to listener fatigue. A vent is present on the Apex modules to equalize pressure; viscoelastic open-cell foam is placed in the vent to both retain the low-end frequencies and control the release of air. The M20 has a single vent, the M15 has two vents, and the MX likely has three vents. The trade-off is a minor loss of isolation in that order. This technology works. I can wear the 64 Audio IEMs significantly longer than other IEMs with minimal fatigue.
The measurement below was taken off of an IEC-711 coupler. There is a resonance peak at ~10kHz and, as such, measurements after this point should not be considered entirely accurate.
The burning question in most reader’s minds is no doubt whether the U6t is a baby 64 Audio U12t. After all, as many will attest to, the U12t is the de-facto gem of 64 Audio's lineup that competes with - and straight up surpasses if you're asking me! - some of their even more expensive models. Well, the answer to that is more nuanced than a straight yes or no. I’d say it’s more a mesh of the Nio and the U12t. What makes it more difficult to pinpoint is that you're afforded two distinct sound signatures with the U6t thanks to 64 Audio’s Apex modules. With the M15 and M20 modules, the U6t can be considered a warmer, thicker, U12t that takes inspiration from the Nio’s bass shelf. Plug in the MX module, though, and you have a leaner signature that hits much closer to neutral-warm. I'll mostly be speaking with reference to the M15 module, my preferred module.
The bass on the U6t is good. Well, that’s an understatement actually. It’s really good for BA bass. Most are aware of my appreciation for the U12t’s bass, which is some of the finest BA bass out there. Likewise, I wouldn’t be too surprised if the U6t was using the same BA drivers. The U6t definitely doesn’t have the cleanest bass lines thanks to a good amount of mid-bass presence, but the roots - the slam, the texture, and that organic sense of macro-dynamics - are all there. Particularly with the M20 module (which admittedly, I’d steer away from using because it muddies the U6t's presentation more than I’d like), the sheer decay, oh my. The issue you run into with a lot of BA IEMs that boost the bass excessively is that they end up sounding quite plasticky and still have truncated, atrocious decay. Not the U6t.
Moving into the midrange of the U6t, it's characterized by a generous, smooth transition from the mid-bass to the lower-midrange. This is why I say the U6t is more characteristic of the Nio, at least sub-1kHz. Past this point, you do have something that is more reminiscent of the U12t: a fairly gentle pinna compensation and a slight recession to the upper-midrange. The end result is a warm, saturated midrange presentation with which vocals are thicker than life if not incredibly pleasant on the ears. On something like Loona's "Eclipse," for example, the vocalist Kim Lip exhibits some sibilant characteristics in the opening lyrics "I feel sparksss" that can come off as undesirable on IEMs that choose to elevate the midrange (even on ones that slope off 3-4kHz fairly gently). Not a chance with the U6t, and credit where credit is due, at this point in time, I cannot think of a midrange I prefer more for the price point. Yes, it might help that much of my library admittedly consists of high-pitched female vocals and unabashed shouty-ness. But those who felt the Nio's midrange was too thick or the U12t's midrange too thin might find this to be the ticket too.
The U6t follows the U12t’s treble profile pretty closely. You have a 5kHz peak followed by a subsequent dip throughout the mid-treble frequencies, so there’s not much sparkle. If that was all, then this would be a very dark IEM. But right at around 14kHz, the treble starts coming back up, plateauing with considerable amplitude at 15-16kHz. The end result of this is a very unique treble experience. It’s incredibly detailed and quick for a BA, although it’s decidedly not perfect. On something like Everglow’s “DUN DUN,” for example, the shimmer can be fatiguing on the hi-hats (or the result of whatever ungodly edits have been made) to the left from 2:30 to 2:48. I would recommend playing around with the modules, as well as ear tips, to see what works best for you. Remember: this peak is pretty high-up, so some listeners might not even hear it altogether!
Let’s get something out of the way: for sheer note definition, the U6t is simply not the strongest performer. Attacks are slightly brushed in the bass and, particularly in the midrange, there’s definitely some blunting going on. That’s equal parts a consequence of the thicker tuning and the drivers being used in the U6t. There’s plenty of kilobuck stuff, heck, even sub-kilobuck stuff, that has the U6t beat here. See the Moondrop S8, the Thieaudio Monarch, or the Unique Melody MEST if all you’re looking for is good resolution.
But something one notices about most of these other IEMs is that they sound...flat. They sound compressed. They sound boring. And yes, I’m talking about dynamics. Dynamics are the variations in loudness of a given track and a given transducer’s ability to replicate them; they’re the foundation of engagement factor and what gets our head bobbing. If you’ve ever heard a speaker system, then you’ll know there’s usually no comparison to IEMs when it comes to dynamics. And yet, the U6t has dynamics. I don’t know how 64 Audio does it, but I can’t stop talking about it.
Recently, I’ve been listening to Sawano Hiroyuki’s 2V-ALK album and the track “e of s”. This master actually has higher dynamic range than the remastered version, and I definitely picked it up on the U6t. At 2:48, the range of Mizuki’s voice dips slightly on the last “ohh, ohh, ohhh,” before the track explodes into loudness. The U6t doesn’t scale this subtlety as low as some other IEMs I've heard; however, there is a good sense of visceral energy to the subsequent eruption in loudness. Likewise, on a track with a slower, more subtle sense of dynamics like Taeyeon’s “Gravity,” it feels like each heavy note from the bassline is slamming you over and over. This is a stark contrast to many other IEMs I hear which fail to convey that innate sense of, well, gravity to the track.
Another aspect of which the U6t shines is timbre. By virtue of the sheer warmth or the slightly slower attack and longer decay of the BAs that are being used, the U6t has surprisingly very little BA timbre. This is a sort of metallic straining effect, plasticky-ness, to notes that many other BA IEMs exhibit. Heck, I’d say the U6t has even less of this quality than its older brother, the U12t, which is one of the cleaner BA IEMs.
For staging, the U6t leans toward the more intimate side. It’s not on par with the U12t, much less 64 Audio’s IEMs like the Tia Trio or Tia Fourte which make use of acoustic chambers. That being said, I find that there’s enough ambiance to keep me satisfied with the M15 module. There are a couple reasons for this, and I’d hypothesize that they’re largely baked into the U6t’s tuning:
The more relaxed pinna compensation begets a more diffused presentation. This is further aided by the slight upper-midrange recession, which helps to create the illusion of a center image and greater soundstage depth.
The tia treble response has unique peaks and valleys. The mid-treble recession and subsequent contrast to the air frequencies lends to some interesting reverb and, by extension, to the way the stage is imaged.
And if there’s still not enough staging, you can always pop in the MX module to open things up even further at the expense of bass quantity.
Assessment of Value
I’ve already illustrated why I think the U6t is a step ahead of the “emerging” IEMs in the sub-kilobuck bracket even if it might not be quite up to par in the resolution department. That in mind, let’s take a look at some of the heavy-hitters that token the U6t’s price bracket more closely:
The Andromeda 2020 is clearly going for a different type of sound. It is a more open, holographic type of presentation that sacrifices dynamics. Honestly, while I dislike using the term “night and day,” that would describe the difference between the Andromeda 2020 and the U6t’s dynamics. These make good foil IEMs to one another in my opinion.
The IER-M9 probably aligns most closely with the sound that the U6t is going for. It has a warm, smooth type of presentation that likewise only stumbles a tad in the treble. The IER-M9 actually even has cleaner timbre than the U6t and pinpoint precise imaging that makes the U6t seem congested by comparison! But...again, dynamics. A characteristic that listeners of the IER-M9 will consistently echo is that it is eminently well-rounded, yet oh-so-boring in its presentation. Go for the IER-M9 for the better IEM on paper; go for the U6t if you're after a more musical, engaging sound.
Last year, the MEST shocked many listeners with its sharp resolution and out-of-head imaging. I have to admit: I was pretty impressed too. Head-to-head, I think many listeners would gravitate toward the MEST for its immediate "wow" factor. That is, of course, until the flaws started presenting themself. The MEST is simply not very coherent. Its DD woofer skews considerably slower than its quicker midrange BAs, it has a tendency to exaggerate the separation of instruments to the point of which its unnatural, and it has some timbre issues from the midrange up. Ultimately, I prefer the U6t, but I'm not going to say that it's better than the MEST, and I could easily make a case for the MEST if I was just listening short-term.
I've heaped no shortage of praise upon the U6t. To touch back on the introduction of this review, what only makes this more impressive is that the U6t is actually a couple years old! If you’re not familiar with the world of IEMs, that’s a long time. It just goes to show how far ahead of the curve 64 Audio was at one point. And here, I want to give a more sober perspective. I want to challenge 64 Audio to once again get hopping on some actually new IEMs because, as the U6t effortlessly demonstrates, they can definitely tune and they are one of the few brands prepared to propel the IEM world into a new era of sound. But that's just my opinion. Either way, the U6t definitely has my recommendation; it'll be going down as one of my new favorite IEMs.
Buy the 64 Audio U6t for the best available price.