64Audio U3 In-ear Earphone Review

Sound –

64Audio’s naming scheme is simple, the U3’s are their 3 balanced armature driver universal model with a 3-way passive crossover. The U3’s implement a number of technologies pioneered by 64Audio’s customs, their quad bore design and APEX module, in particular, making a notable difference in sound quality and character over more conventional models. It’s also interesting to see how coordinated 64Audio’s universal line-up is. For instance, the U3 carries a more balanced sound and the U4 a bassier one with higher models, in this case, the U6 and U8 respectively, carrying similar tonalities but with increased technicality and refinement. This makes finding the right model and upgrading much easier since 64Audio do have quite a number of models on offer. Subjectively, the U6 has my preferred tuning though the U3 provides much of the same strengths at a significant discount and their innovative features and fabulous tuning do grant them with several key advantages over similarly priced in-ears from other manufacturers. I actually found the U3 to be tuned relatively similar to the Sennheiser ie800, and while it is a considerably cheaper and far better fitting earphone, I thought it would make for some interesting sound comparison.


Burn-in –

I let the U3’s burn-in for around 150 hours before my final review. I do not feel like the earphones have responded significantly enough to comment. Buyers should expect consistent long-term performance and perfect channel matching with replacement earpieces.


APEX Modules –

Perhaps the most unique feature of the U3’s design is their proprietary APEX modules (those silver cylinders protruding from the sides of the earphone), which are exclusive to all of 64Audio’s earphones. On the surface, the modules enable basic tuning of the earphone’s sound though their technology is far more useful than a pure filter. This is because the modules are also designed to reduce listening fatigue and improve phase while retaining noise isolation; it’s a very interesting concept that combines the benefits of vented and fully-sealed earphones. At present, 64Audio offer two modules; The M15 (grey) which is more open granting an airier sound and less isolation and the M20 (silver) which is more balanced and isolates considerably more. The U3’s come preinstalled with the M20 though I found it to be the better pairing to the U3 than the M15 and the added isolation is welcome. The M15 is available for $99 USD should you want more air and clarity.

In use, I found the modules to enhance comfort as the U3’s don’t produce the pressure during wear that the sealed Plussound’s, Campfires and Audiofly’s do, even with silicone tips. The U3’s are also surprisingly unfatiguing considering their treble lift and resolution in addition to their more aggressive tuning. That being said since the modules do protrude slightly from the sides of the earphones, the U3’s did produce more wind noise than these other earphones when running. I’m still a fan of the technology and the U3’s are significantly quieter and far better isolating than other vented earphones like the ie800 and DK-3001 while being a little more listenable long-term. The modules are also easy to remove and replace though they fit very snugly within the housings and don’t budge during abrupt motions. The APEX modules are pricey, but they are a well-designed and implemented idea that produces genuine real world advantages.


Tonality –

The U3 is a very balanced in-ear with a slightly U-shaped signature. They have a particular emphasis on sub-bass with a slight dip in mid-bass fullness and mids are present and clear with slightly thinner body. High frequencies tend to direct attention though not due to any huge emphasis but due to their outstanding clarity and resolution. Highs are slightly lifted but they avoid coming across as peaky or splashy. As such, the U3 is very clear and revealing earphone though not a particularly fatiguing or strident one.


Soundstage, Imaging and Separation –

The 64Audio’s have a nice soundstage that is well balanced between space, coherence and placement precision. Those APEX modules, even the slightly more closed M20, grant the U3 with notably more space than most sealed earphones. The U3 has noticeably strong width that reaches outside the head on a lot of material and nice depth although not quite as much as the exemplary AF1120. They don’t possess a huge amount of height though few tracks really call for it. Imaging is great as one would expect, instruments are precisely placed and easy to locate though centre image isn’t quite as strong as the Campfire Jupiter and AF1120. Their most standout trait amongst competitors is their separation due to their great dynamics and end to end extension combined with their spacious presentation. Instruments during complex passage were more delineated on the U3 than the slightly busier DK-3001 and the more mid-forward AF1120. They still don’t best the exemplary Jupiter which also has a few unique technologies augmenting performance, but they perform favourably to similarly priced models and are leaps and bounds above cheaper in-ears.


Drivability –

The U3’s are very sensitive at 114dB and possess a very low 12ohm impedance. But despite their impedance and 3-way passive crossover, the U3’s u-shaped sound found better synergy from a wider range of sources than the more neutral AF1120. They were also more forgiving of lower quality sources than the Audiofly’s were due to their slightly high sensitivity and lower current demand. Of course, the U3 has plenty of resolution to take advantage of a better source, but a particular tonality isn’t required to find a pleasing pairing. Of the sources I had on hand, I most preferred to run the U3’s from my Chord Mojo which has a smoother, more neutral sound with a hint of extra body that synergized well with the U3’s cooler midrange presentation. The Fiio X7 and Oppo HA-2 also provided nice pairings, particularly with regards to bass definition though their high-end presentations, particularly the Oppo, lacked the refinement of the Mojo. The U3’s also sounded fabulous from my HTC 10 and even my iPod Nano 7G offered a pleasing sound that was clean and well detailed. They U3 is quite sensitive to hiss and benefits from a quiet, high-resolution source with a smoother high-frequency presentation.


Bass –

Tonally, the U3 is quite interesting, they are somewhat similar to the Sennheiser ie800 but with considerably less emphasis throughout. Sub-bass has the most emphasis and mid-bass is about neutral with a slight lift into upper-bass granting lower mids with a little extra body without spill or noticeable warmth. As such, bass doesn’t sound as voluminous as the AF1120 but bass has terrific slam and impact. Sub-bass extension is also some of the best I’ve heard from any armature earphone though of course, they don’t quite have the subterranean response of the dynamic ie800 and the hybrid driver DK-3001 with its 13mm bass driver. This was most noticeable when listening to The XX’s “Islands” where the U3 produced rumble, impact and solidity that the AF1120 and Prism didn’t even glimpse. And besides sub-bass, the U3 continued to impress with excellent texturing, resolution and detail. Where I had previously considered the Prism and AF1120 to have more outright texture and bass detail, after more extended listening with the U3, that is not necessarily the case. Both of those earphones are slightly more linear in the low-frequencies and as such, intricacies are more consistent. The U3 has very similar texturing and bass detail retrieval but the nature of their bass response puts uneven weighting on details in certain frequencies which can provide the impression of a slightly less nuanced listen. However, after some adjustment to their sound, the U3 is certainly no less impressive than either of these earphones and I personally prefer the extra sub-bass to the slight texturing advantage of the AF1120 and the slight resolution bump on the Prism. In addition, the U3 has a quick bass response that keeps up well with complex passages and rapid bass transitions. And despite their added sub-bass, the U3’s lack of mid-bass bloat makes them exceptionally snappy. The U3 is just a little looser than the tighter AF1120 but their low-end was similarly cohesive as the Prism during a variety of genres of varying mastering quality. If you are looking for outright texture and detail, perhaps the AF1120 will fit the bill, but the U3’s slightly more vivid and notably more extended response is toe-tapping, engaging and just as technically proficient if at inherent disadvantage due to the slightly uneven nature of their tuning (again, the U3 is very balanced, these comments and differences are minute).


Mids –

If you’re looking for absolute neutrality, the U3 is not the most realistic and natural earphone, but it is one that is engaging and wonderfully technical too. The U3 has a delightful midrange with exquisite clarity and great balance between upper and lower mids. I was initially inclined to call them a slightly brighter earphone, and perhaps they will be to some ears, but they put similar emphasis on tracks with both male and female vocals in my testing. And coming back to that clarity, the U3’s have a clean, clear response that really flatters genres like pop and compensates for the slightly more veiled presentation of jazz. Listening to Frank Sinatra’s “My Way” and the U3 proved to be surprisingly uncompromised considering the level of clarity on offer though the more expensive Sennheiser ie800 managed similar levels of clarity while remaining a bit more tonally correct through its greater midrange body. Similarly, the AF1120 was slightly more natural and defined, though they can sound a bit dry on other tracks (more the mastering than the earphones themselves). The slightly more vivid U3, on the other hand, provides just that little extra to songs with blander mastering all the while avoiding overstepping their boundaries on more vibrant tracks.

But while they never sound off, I still think the U3 sounds a little thin through its midrange, the extent to which will vary with source material. This is more an issue with the upper midrange than lower mids and even female vocals never sound hollow or nasal, but small deviations from neutral are clearly noticeable at this level of sonic finesse. Usually, I would be more critical of this fault, especially given the U3’s asking price, but the U3’s midrange has some interesting qualities that somewhat offset their thinner body. Perhaps most notably, vocals and instruments are very smooth which really helps to take the edge off their enhanced clarity, preventing the earphones from tiring and fatiguing. And while vocals are slightly raspy and missing somebody for my tastes, this smoother character combined with the U3’s great detailing and resolution grant vocals with a lucid creaminess that is both unique and highly enjoyable; I personally found this tuning to be more rewarding that that of the DK-3001 which didn’t sound a consistent and clean. They are still missing some body and richness for instruments like acoustic guitar, but for vocals, piano and lower strings, the U3’s provide a fine rendition. So the U3’s aren’t neutral or natural, but they are certainly very enjoyable and they are definitely one of the best clarity orientated earphones I have heard.


Treble –

Usually, I start writing my audio breakdown from bottom to top, but for the U3, I thought it fit to start the other way around. The high-frequency presentation of the U3 is sublime; airy and crisp with great attack with exquisite resolution. Treble notes are forward but not overly so, even coming from the laid-back AF1120, and they never became fatiguing to my ear. Perhaps this can be attributed to those APEX modules or simply superb tuning on 64Audio’s behalf, either way, for lovers of detail, air and clarity, the U3 is stunningly insightful and delicate. The DK-3001 provides the aptest comparison as another slightly more aggressive in-ear with dollops of treble detail. While I still find the DK-3001 to be very slightly more detailed, the U3 is appreciably more separated and airy, it is the more extended and refined sounding earphone. When listening to “Disconnect” by Clean Bandit, the U3 also had more delicate treble than the Dunu and a smoother rendition of strings. They actually presented similarly to the incredibly resolving ie800 but lacked the splashiness and slight metallic tone that sometimes affects the Sennheiser. The U3 had more treble body than the ie800 and while it still lacked a little bit of resolution and detail compared to that model, each high note on the U3 was more lifelike and textured. The U3 was also notably more separated than the exemplary AF1120 who’s more laid back, depth focussed presentation lacked some air.

I also found myself impressed by the consistency of the U3’s treble insinuating quite a linear response. As a result, the U3 finds great versatility with a wide range of genres, equally flattering the cymbals in Radiohead’s “Creep”, the ringing high-hats in Nirvana’s “Lithium” and the ethereal keyboard in Frank Ocean’s “Pink + White”. Great treble extension should be a given at this price point though the U3 has really fantastic extension even amongst similarly priced competitors with essentially non-existent roll-off. Combine that with fantastic resolution, class-leading treble air and a surprising lack of fatigue due to those proprietary APEX modules and the U3 provides one of the most rewarding listens for jazz, rock and acoustic.

Next Page: Verdict



Ryan Soo

Ryan Soo

Avid writer, passionate photographer and sleep-deprived medical student, Ryan has an ongoing desire to bring quality products to the regular reader.


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