64 Audio U4s

64Audio U4s Review




Prelude:

64Audio is probably amongst the most famed IEM manufacturers as of today. Not only are they are a popular brand amongst audiophiles, they also make custom monitors for some of the most renowned artists and producers out there. Personally I’ve tried the U12t, U6t, Duo, Fourté Blanc, yet, save for the U12t, none of them have truly impressed me. To me, their products mostly still stay within the realm of “luxury”. While their IEMs are actually all good, or even fantastic, they simply don’t have a high price-to-performance ratio. Even for the U12t, while it’s still amongst the best of the 185+ IEMs I’ve tried, it’s 2000 USD price tag is also too hard to swallow for me. Can the U4s, 64Audio’s newest and most inexpensive UIEM, change my thoughts on this brand and their products?


Unboxing:

64Audio’s unboxings are boring to a point where I don’t really want to take photos of them. IEM, in a plain, black magnetic-latched cardboard box, with a sleeve on top. Yep, that’s about it. Little presentation, little excitement. Just another day, another IEM box into the bin. Within its price brackets, I’ve seen a lot better. Take a look at the EA Gaea’s box, it at least has an entire face that is embossed in gold, having a fancy pattern resembling that of the Mother of Earth. Or the SoftEars Turii, which has a twisting mechanism that unlocks the IEMs, fitting the overall design theme. Or the Elysian Diva, which is neatly packed into a cube with multiple layers for you to explore. Heck, even some cheaper IEMs, such as the MoonDrop Variations and the Tanchjim Prism, have better organization and more interesting layouts. The worst thing is that the U4s shares literally the same box as the Duo, U6t and the Nio, while their high end IEMs (U12t, U18s/t, Trio, Fourté) share a larger, but equally boring box. At these high price points, I do think manufacturers should try making their customers feel like they’re getting their money’s worth. Unfortunately, 64Audio doesn’t make me feel like I just dropped 1100 USD on an earphone.


Accessories and Build Quality:

At least the accessories themselves are not bad. You get a 3.5mm “Black Premium Cable”, a leather case, 3 different types of eartips, 3 sizes each, apex modules (mX, m20, m15 is preinstalled on the IEM), a shirt clip and a cleaning tool.

The cable itself is relatively soft, but still kinks and has some microphonics. The y-split, and the termination shells are made out of aluminum, while the pin cases are made out of injection-molded plastic. No machining marks or imperfections are observed on the cable, making this a decent stock cable. My biggest gripe is only having the 3.5mm option at check-out, thus the end-user has to pay more to get a balanced cable. I even asked 64Audio directly whether it was possible to directly ship me a U4s reterminated to 4.4, the answer was unfortunately, no.

The three different eartips are regular silicone, TrueFidelity foam, and SpinFits. The silicone tips are worth mentioning for their atrocious design. First of all, it’s incredibly thin, so thin to a point where it constantly breaks seal (basically 7 out of 10 times I fit this, it doesn’t seal). Then the surface texture is also pretty poor. In those rare times I am able to get a good seal, I can’t use these tips for more than half an hour, when my ear canals start to feel warm. Back to the drawing board, 64 Audio. The foam tips are not bad, even though I can’t find any justification for their 15 dollar price tag (MoonDrop’s MIS-Tip T41 does basically everything these “TrueFidelity” tips do, but for half the price). The SpinFits are honestly the best match for 64 Audio UIEMs, not only are they able to fit the abnormally-long nozzles, the material and thickness are all well-controlled for a good fit and seal. Too bad that they don’t sell these smoke-grey CP-100s anywhere else

The stock case is made out of simulation leather, with nice handfeel. Unfortunately the build on this case isn’t as good as I thought. The 64Audio isn’t stamped in the middle, some of the threading is loose, the edges where the leather strips connect with each other feels a bit rough, and the case itself takes quite a lot of force to open. To the very least, I don’t think this is 49.99 USD levels of good.

The apex modules are made out of machined aluminum, are color-coded and have two rubber rings that seal it within the socket on the earphone. It is hard to believe that a tiny piece smaller than that of my pinky fingernail is worth 100 bucks retail, so try not to lose them! (Editor’s note 9/4/2023: I discovered that one of the m15 modules has a bent edge, not sure if this is due to usage or a manufacturing defect, but definitely do also be beware that these tiny aluminum barrels are quite delicate)

The earpieces themselves are crafted out of sandblasted aluminum, and have a “Slate Blue” paint along with a faceplate inspired by the “Muonionalusta” meteorite (in reality, they look very much like carbon fiber fragments). Personally I think the overall is quite sleek, but also a bit understated, as the faceplate patterns are not very visible, unless under bright light. But the build quality on the earpiece is a bit middling in my opinion, as I believe that build quality isn’t just the selection of materials, but the texture and evenness of the finishing. The part where the nozzle meets the filter is quite rough, as observable small pieces of plastic are sticking out. The faceplate cover is just slightly larger than the body, thus there is this gap at the seam. Rough machining marks are observed, especially at the transition between the nozzle and the main body. And this isn’t just a problem with my personal unit, both demo units I tried in the past have the exact same build issues stated above. I have seen 64Audio CIEMs, and they are quite impressive in terms of build, tidy internals, no observable bubbles within the resin, smooth polishing everywhere… Not sure why their UIEMs have build quality issues I totally didn’t expect at this price. :|

Overall, I can say that I am not impressed with the build of the U4s and its accessories, maybe even a bit disappointed.


Fit:

I might be amongst the only few people on the planet who don’t like the fit of 64Audio UIEMs. My ears are more wide than tall, thus am able to fit fat IEMs like the SoftEars Turii, Cerberus etc., MoonDrop Solis 2, the Vision Ears Elysium, EXT and the Oriolus Traillii with absolutely no problem. But 64Audio’s UIEM design touches my antihelix, causing slight discomfort over time. I think if they added a larger radius to the fillets around the edges facing the ear, these problems might be alleviated. Another potential point of concern is how the vent of the dynamic driver is at the top of the shell, thus due to everybody’s unique ear anatomy, some ears might block this vent and change the bass response. As always, try before you buy.

*Editor’s Note: 9/17/23, after swapping out to the Null Audio Epsilon cable, the fit of the IEM noticeably improved, no more antihelix fatigue. This is because the earhook on the stock cable is far too narrow, thus pulling the IEM into the shallower/narrower parts of my ear. By using a wider earhook (such as the Epsilon’s), the earphone now seats itself in the widest part of my ear, thus eliminating the sense of fatigue generated by the IEM pushing against the ear.


Equipment:

DAC/Amps: LP W2 & W4EX, Shanling H5, iBasso DX170, Tanchjim Space, ddHiFi TC44C (Blue)
Cable: MoonDrop PURE6 / Null Audio Epsilon (both terminated in 4.4mm)
Tips: Eletech Baroque, SoftEars U.C.
apex Module: (primarily) m15

The U4s is an earphone that is very easy to drive. Phone direct outputs can drive it well-beyond recommended listening levels, nevertheless, dongles.


Above is the Frequency Response, and Channel Matching of the U4s, generated by a Clone 711 Rig, tested at 104dB SPL. Green for Left, Red for Right. In general, the U4s sports fairly good channel matching with the Left/Right earpieces matching each other closely with a difference of <1dB for most of the audible range. The maximum discrepancy is at 16.13kHz, with a difference of 1.4dB, although treble measurements are not reliable. Thus, the listener shouldn't be able to discern channel imbalance during regular listening. This shows 64 Audio's high acoustic standards and quality.


Tonality:

Well, what is the point of any audio review without talking about sound quality?
On this front, at least, the U4s delivers.

And its most eye-catching, or should it be ear-catching, aspect is its bass. The U4s’ bass is nothing short of exemplary. It slams, it rumbles, it has decay, plenty of it, and to top it all off, you can change the bass response’s magnitude. Yet further analysis shows that the U4s is slightly different from most of the top-quality bass responses I’ve heard thus far. It is somewhat soft in that it doesn’t slam as hard, rather it makes this up with more rumble and growl, creating a somewhat more meaty and thick bass response. Yet, if too much slam is sacrificed for density, you end up with dirty bass, or even worse, a sense of bloat. The U4s is devoid of bloat by striking a delicate balance between the two metrics. And it has fantastic levels of control that makes every drum kick sound precise, detailed and earth-shaking. The U4s earns a full score of 10 from me for bass. It is not only amongst the best within its price point, it is amongst the best I’ve heard, and has a special flavor to it that just makes things even more interesting. (All based off the m15)

The bass response can be changed via the apex modules, which also change the isolation levels. The mX module (black) offers the least isolation and least bass, while the m20 module (silver) has the opposite. The m15, despite having isolation levels in between the two, has a bass response very similar to the m20 (about 1-2 dB less). Unfortunately, the m12 module that was featured in many reviews and early units, was not shipped to me (I think this might be an early-bird promotion item that was in limited quantities). But telling from frequency response graphs, it creates a bass response that is right in between the m15 and the mX. The mX module creates the cleanest sound out of them all, making the U4s sound like an IEM that is primarily focused on the upper harmonics. I can imagine that the m12 is similar to this, but has some extra energy in the low-end to balance everything out. The m20, despite with a seemingly-negligible 2dB increase, does actually create an even punchier bass, although its tradeoff is that notes may, at times, sound a bit fat or excessively large. While as a big basshead myself, I definitely do prefer the m15 or the m20, but having the option to choose what sound you like for what genre, is definitely a big plus, especially for an IEM that has a versatile sound signature to boot.

The mids on the U4s are a bit plainer in my opinion. While the lower-mids are relatively clean (and can be even cleaner if you use a less-isolating apex module), the upper-mids have an early peak at around 2.15 kHz, followed by a 3.3kHz dip. On first listen, the U4s sounded relatively natural to my ears, but further A/B testing and analysis made me feel like something was always slightly lacking. That something is transparency, not in the sense of raw detail retrieval, but of simply how vocals stand out from the rest of the mix. This does make vocals sound a bit dull, powerless and generally smoothed over. It’s not only the U4s, but many similarly-tuned monitors, such as the SA6 (OG & MkII), MEST MkII, and most other 64Audio UIEMs, exhibit these very traits. While I do understand why this tuning is chosen for the U4s and all the other monitors mentioned (to reduce shoutiness and create a more laid-back tone), I am not its biggest fan. 8 out of 10, as while it does sound neutral enough, it is not an embodiment of excellent nevertheless perfect mids for me.

The treble on the U4s is quite polarizing too. To put it simply, it is uneven. A peak at 4.5kHz, a dip at 5.5kHz, some elevation at 6 to 10kHz, then a massive treble spike at 16kHz. Yep, all of this makes the U4s stray far away from the descriptor: neutral. But beyond slapping generic terms to describe the U4s’ treble, it is quite hard to correctly pinpoint what it exactly does. The 4.5kHz peak adds some harshness to vocals, the 6-10kHz elevation and the 16kHz spike generates the sense of snap and pushes forward treble detail. Yet, the 5.5kHz dip kills sibilance, while the 12k – 14k basin does occasionally make the reverb of instruments sound a bit smoothened. However, there is no denial that the U4s has excellent extension, and thus a lot of air. It’s decay function is also interesting, in that there are some extra trails behind notes, despite its sharp attack, giving this refreshing treble texture that I have yet to hear in most other IEMs. To sum it all up, it is an interesting yet colored tuning, that can be fatiguing at times, 8 out of 10. People around me either love or hate this tuning. Those who love it say it’s because the sheer air and detail the U4s generates exceeds lots of expectations at this price point and for a single BA. Those who hate it say it’s because the treble sounds too unnatural, almost like broken glass shards: so excessively sharp to a point where fatigue turns into pain. As always, try before you buy, this might be the very sound you’ve been looking for, or might be one that is definitely not your cup of tea.

Timbre on the U4s is generally quite good. Despite being a BA-DD hybrid, I don’t hear a lot of the maligned BA timbre that plagues most IEMs of the same architecture. However, due to the significant treble peaks, the U4s’ timbre does have a noticeable metallic edge, especially for hi-hats. Another issue with the U4s’ timbre is coherency. While the bass is exceptionally meaty with lots of decay, the mids and treble have quicker transients and thinner note weight, thus making the sound feel a bit disjointed. Overall, the U4s retains a relatively good timbre, 8 out of 10.

The tonal balance of the U4s is not exceptional in that I don’t quite feel like every frequency band is complementing each other. It’s bassy, laid-back, and peaky all at the very same time. Yet, this is also why the U4s is unique. It is a daring IEM that pursues a sound that few have tried to implement, and it does it fairly well.

And it has the technicalities to back everything up.

Not one IEM from 64Audio’s lineup sounds compressed, and the U4s maintains this trend. I daresay that it handles dynamics even better than some of its more expensive brothers (namely the U6t, which I found to be a bit flat). Macrodynamics on the U4s are exemplary, notes sounds explosive and alive. I think this is partially because of its generous extensions on both ends. What’s interesting is that its midrange, despite being fairly recessed, still sounds relatively dynamic (as recessions often cause a decreased perception of dynamics). The U4s’ dynamics are interesting in its own way, of how it has this sense of excursiveness behind notes, which makes them sound slightly larger than life. Microdynamics are just as good. Microdetails are incredibly well-defined and have large gradations of volume. I presume that the tia treble has quite a lot of influence in the perception of said microdetails, as it presents high-frequency notes with an exaggerated sense of snap and crispiness. Overall, I am satisfied if not even impressed by the dynamic range the U4s is capable of presenting. 10 out of 10.

Excellent imaging is also a trait of 64Audio IEMs. Large soundstage, incredible layering and positional accuracy, great diffusal and height… the U4s has them all. However, I don’t think the U4s’ imaging performance is better than its 64Audio brethren. The U12t definitely pushes further on all of the aspects mentioned above, the Duo has more space between instruments, and the U6t has slightly better positional accuracy. Nevertheless, the U4s’ imaging performance is great, 9 out of 10.

Resolution is another strong suit of the U4s. Although its bass and mid resolution is particularly outstanding, the treble that is powered by the tia driver is incredibly detailed. All notes, especially percussions have excellent snap and definition. Yet, the tradeoff is that the treble can also be the most fatiguing part to listen to the U4s. Another observation I’ve made after tip-rolling, is that the deeper the insertion, the less treble detail, but at the same time, the smoother it gets, and thus, less fatiguing. I use a medium-shallow insertion which gets a lot of treble detail without overdoing it. The U4s’ resolution is competitive with other IEMs in its price bracket, even though its mid detail might be behind others. 9.5 out of 10, it is detailed enough for me.


Comparisons:

Effect Audio x Elysian Acoustic Labs: Gaea: out of the 185 IEMs I’ve heard, I still maintain that the Gaea is the best (that pool of 185 includes stuff such as the Trailli, Z1R, Phönix, U12t, Ronin, CP622B, Jewel, Rn6, Odin, Turii Ti, Loki, Trifecta, Fourté etc.) (I am still trying to find a chance to listen to the Storm and Elysian’s own Annihilator). The U4s definitely doesn’t hit my tonal preferences as close as the Gaea does, as it has a myriad of very minor tonal quirks that when added together, makes it sound slightly more colored. While the treble on both are all exceptionally well-extended and detailed, the Gaea’s doesn’t exhibit fatigue unlike the U4s. The mids on the Gaea are nothing short of beautiful, yet the U4s’ mids sounds a bit too laid back and somewhat dull. However, it’s the bass where the U4s eclipses the Gaea. The Gaea’s ultra-fast transients smears texture, while the U4s has lots of growl and rumble, bringing a much livelier, foot-tapping experience. In the technicalities department, the two start trading blows. Both are incredibly dynamic. The Gaea focuses more on microdynamics, while the U4s goes for macrodynamics. Both are very strong when it comes to imaging. The Gaea has outstanding layering and positional accuracy, while the U4s simply has a larger stage with better center imaging, height and depth. While the U4s’ resolution falls slightly behind that of the Gaea’s, it is no slouch. All in all, the U4s sounds like a wonkier, yet more exciting iteration of the Gaea’s mid/treble-focused sound.

SoftEars Twilight: Probably the hardest comparison I’ve come across, as these are two completely different IEMs. The Twilight is warm-neutral in that it has some treble roll-off, a massive soundstage, with slightly blunted transients to create a butter-smooth sound that I can listen for hours on end. The U4s has loads of upper-treble and sharp, well-defined transients. It is one of the last IEMs I’d associate warm and smooth with. I am someone who can wildly change their preferences, so I actually listen to both IEMs almost equally. On the non-sonic front, the Twilight’s accessories are better, the U.C. tips are great, the stock cable is terminated in 4.4, but comes with a 3.5 adapter, the leather case is built better, and the metal components have less flaws when compared to the U4s’.

Sennheiser IE 600: These two IEMs actually target a similar sound. Both are bassy, don’t have a lot of upper-mids, but have a peaky, yet very well-extended treble response. To top it all off, both are incredibly resolving and dynamic. However, I think that the U4s does most of these better than the IE 600. It’s bass is more prominent in the mix, its treble doesn’t induce sibilance, and is better technically (the IE 600’s imaging isn’t great, and its other aspects fall slightly behind that of the U4s). But do keep in mind, that now the IE 600 costs a bit more than half the price of the U4s (headphones.com sells this at 600 bucks, whereas the U4s costs 1100). Even though the presentation and accessories on both are all subpar, the IE 600’s shell fells quite unique and is better-finished than the U4s’.

MoonDrop Variations: I’ll maintain that the Variations still has amongst the most pleasing bass responses on the market as of today. I am more of a sub-bass person, so it hits my low-end preferences almost perfectly, perhaps only losing out to the top dogs, like the Z1R, in terms of control and speed. Against the U4s, I still think that the Variations has the upper hand. While the U4s does have a lot more mid-bass than the Variations, the Variations simply pounds a lot harder, and has ethereal levels of rumble, making it simply sound bassier, even if it doesn’t graph like so. The Variations’ mids follow MoonDrop’s traditional tuning, scientifically-boosted mids with maybe a dash of shout and thinness. The U4s’ is more of an antithesis of this, as it sounds a whole lot thicker and recessed. Then we move onto the treble. Even though the Variations’ treble is tokened by two 2nd-gen Sonion ESTs, they don’t sound quite like a true E-Stat, lacking in the airiness and detail I hear in over-ears, such as Stax’s stuff and the HE-90, even though it is a considerably smooth and fairly well-extended response, and is amongst the better EST implementations out there. Interestingly, the U4s sounds more like an E-Stat than the Variations, probably thanks to its tia driver, which generates that sense of air and detail the Variations lacks. In the intangibles, I do find the U4s to have generally better macrodynamics and treble detail retrieval, although I do think that the Variations has stronger positional accuracy. In the non-audio aspects, despite the Variations using a stainless steel faceplate and a solid resin body, it is significantly weightier than the U4s’ full aluminum shell (probably because 64 Audio uses thin aluminum). However, I did not observe any surface blemishes on the Variations, unlike the U4s.

64 Audio U12t: The U12t is amongst 64 Audio’s most well-known models, and amongst the oldest in their revised UIEM lineup. Many reviewers around me have given high praise to this model, especially for its all-rounder tonality, and top-class technicalities. Indeed, after hearing 2 different units and spending a few hours with them, I can conclude that the U12t is still a very strong contender in today’s high-end IEM market. The thing that struck me first was its surprisingly competent BA bass (often known for its soft and hollow attack, net-zero decay and lack of texture). As a basshead myself, it ticked most of the marks for a high-quality bass response, ultimately still lacking in a bit of decay and slam, but made up with its fantastic bass speed and resolution. The U4s’ bass essentially fixes the two aforementioned problems, giving it a meatier, denser bass response, but lacks the responsiveness I heard in the U12t’s BA bass. The mids are similar, but I think that the U12t’s vocals do pop out a bit more, probably because its bass isn’t as overly dominating to a point where it drags the listener’s attention away, unlike the U4s. Not to mention that the U12t’s midrange is amongst the most resolving out there. The treble on both are similar, but not exactly the same. I didn’t do a lot of very focused analysis on the U12t’s treble mostly because the 15-16k tia resonance peak was too distracting, the very peak a lot of 64 Audio UIEMs share. But from memory, the U12t’s treble was somewhat smoother than the U4s’. In terms of technicalities, the U12t is also steps ahead of the U4s, it has an even more expansive soundstage, better localization, and is significantly more resolving. The U12t is just better than the U4s in almost every way possible, yet also, costs near double the price. I am comparing the two not because I believe that the same customers that are looking at a U4s might buy a U12t, rather it is because I want to see how companies distinguish their products, from entry-level to high-end to flagship, and how they are able to justify the pricings/status, and on that front, I believe the U12t firmly justifies its status as one of the high-end models of 64 Audio.

64 Audio U6t: From memory, this was amongst the least-impressive 64Audio’s I’ve come across. Yes, it’s well-tuned, yes it’s relaxing and very easy on the ears, but the U6t sounds almost too flat. And that’s exactly why I think the U4s is significantly better than the U6t. It is a more versatile IEM in that it fits more genres, primarily due to its improved bass response, but also due to its tonal balance. My definition of tonal balance isn’t simply how good the overall tonality is, rather, it is how well each individual frequency band is and how they complement each other. In this regard, I think the U4s is more balanced than the U6t. The U6t doesn’t have a lot of bass (even though the FR suggests so), and isn’t as well-extended as the U4s, thus it creates this mid-focused sound, yet it doesn’t have quite a lot of mids to pull this signature off either, making it sound somewhat weird. The U4s has a slightly more recessed midrange, but has plenty of extension on both ends to make this type of sound signature work (V-shaped). In terms of tonality, I think the U4s is more preferable for my library. But in terms of technicalities, I think the U6t falls behind even more. Its dynamic contrast isn’t strong enough, oweing to its lack of extension. Its resolution isn’t as good as the U4s, probably due to its smoother treble and mid response which makes details harder to capture. Its staging is, however, better than the U4s, but not marginally so. The stage size, central imaging, and layering are all a small step ahead of the U4s. All in all, I don’t think the U6t is anyhow better than the U4s, despite its 200 buck price increase. In fact, I think its worse. My recommendation is: buy the U4s, its sounds better, looks better, and is cheaper.

64 Audio Duo: The Duo is an interesting IEM to the very least, unlike the U6t. It has a near-ethereal stage size, that outclasses most IEMs I’ve heard in its price category, including the U4s, however its tonality and the other technicalities don’t. Its resolution is more reminiscent of a 200-buck single-DD, its dynamics, while are good enough, still sound slightly compressed, its mids sound much more recessed than other 64Audios, its bass is great, but not on par with the U4s, and has the signature 64Audio tia treble (read: very spicy up top, but this time without a lot of resolution to pull it off well). While the Duo offers a cool faceplate design, and offers probably the golden isolation level of -12dB (just enough to not make you feel totally disconnected from the outside world), in terms of sound quality, the U4s is definitely the way to go.

64 Audio Fourté Blanc: Again, from memory, this is amongst the weirdest IEMs I’ve ever come across. The tonality of the Fourté Blanc simply sounds wrong. Its bass isn’t as impressive many other 64Audio IEMs like the U12t or the U4s, despite it being the Blanc’s marketing’s primary focus. To my ears, the 64Audio’s house bass sound sacrifices slam for meatiness and growl, but the Blanc’s bass goes down this path way too far. It doesn’t have slam, and due to its mild bass boost, doesn’t appear to have a lot of rumble either. Then the midrange… honestly, to this day, I am unable to really describe what I heard. It was just… awkward. There are unnecessary recessions that invokes this sense of hollowness and blandness. Whatever 64Audio is trying here isn’t working well for me. The treble at least isn’t as bad as the mids. It’s pretty bog-standard 64Audio tuning, myriads of treble peaks with the largest one being the 15k “tia” resonance. In general, the Blanc’s tuning is just confusing. It’s not particularly bassy, and has a mind-baffling midrange tuning, but at the same time, has a lot of treble? But at least the Blanc’s technicalities meet my expectations of a premium flagship. It has a stage that matches the moniker: “holographic” the closest, has top-tier resolution and good dynamics to back it up. Horrible tonality paired with endgame technicalities puts the Blanc in a very hard spot for me to assess. Enough of the Blanc mini-review, we’re here to compare it with the U4s. The U4s’ tonality is to the very least, listenable. It isn’t as bad as the Blanc. But in the technicalities department, the Blanc is definitely steps ahead of the U4s, yet this is expected when you are charging more than 3 times the price. New tia driver in place of a standard mid BA, “revolutionary” internal acoustic structure, updated internal wiring and solder, apparently better aluminum shells with ceramic coating, more premium cable, but 2600 USD more and with an eccentric tuning, I just don’t see it. Companies can do so well with their entry-level products, but then fall completely flat on their flagships that are supposed to represent their ultimate earphone tuning prowess. Do better 64 Audio, I hope that the next flagship isn’t a trainwreck like the Fourté series.

(just look at that... gorgeous.....)

it's been long since i wanted a 64 audio iem, been in love with their simple yet helpful APEX module making iems feels and sound more open than usual but... which model???

after trying all of their lineup starting from the lowest till the highest (yes including U18S, fourte etc) funnily enough i find my favorite to be their lowest universal line

please note that i'm more of a tonal person rather than technical... i simply wanna enjoy music not goint surgical and pinpointing microdetails here and there... i simply enjoy U4S the most, i will elaborate later...


Size & Fit :
Basically similar to any other universal 64 audio lineup, medium sized with long nozzle, they are a bit bulky for my small ears yet i could wear them for hours without any complain, maybe only the default cable can be a bit stiff at times, but it's a minor problem


Measurement (graphed using IEC711)
if you're using IEF neutral 2023 as neutral target U4s can be categorized as a mild V iem, elevation in lower freq, slight dip around ear gain 3k area with relatively slightly boosted mid treble and additional upper treble peak to add airy effect

APEX Module :
M20 (-20db) : (light grey) the bassiest one, somehow the smallest in stage, but maybe due to the isolation, sounds the most focused in imaging
M15 (-15db) : (dark grey) is the one that i usually use when using them outdoor, still bassy but more open on the upper frequency)
M12 (-12db) : (golden) u4s exclusive model for now, later will also be available in market, aside m15 i use this m12 the most, not as bassy as m15 overall the best balance for all freq but sacrificing the sub bass of m15 and m20
MX (-10db) : (black) the most open, the most mid forward but the bass is almost neutral at this point, only giving a very slight thump and soft punch

this is an interesting phenomena where the more seal it gets the more bassy it gets but also it sounds more focused in imaging, the more open they are the wider they sound yet the sound gets more blur in imaging

for this review i will be using M12 and M15
Low :
one of the aspect from U4s that hooked me right from the beginning, it is rumbling with somehow unique "atmospheric" bass sensation, fun punchy and immersive, for me this is quite special as its giving a more physical rumble sensation than the usual iem (but this sensation isn't new, similar feeling to the 64 audio trio and nio, not as physical as Fir Radon 6 though)

gotta admit it's a bit slow for rock and metal music, but HECK IT'S SOO FUN!! and i don't listen to rock and metal a lot so no problem for me, for bass only i prefer M20 and M15 the best for its better sub bass presence compared to m12
man i love hearing EDM and electronic music from these, but hearing Disney OSTs like a whole new world somehow feels so special and majestic a

Mid :
now this is smooth, making a 3K dip sure makes this iem has a more relaxed mid compared to my neutral preference but fortunately i can feel the upper mid 5k slight rise maintaining some "vocal edge" when the singer shout, keeping the vocal energy. for a lot of singers this really sounds balance for me, but amazingly opening the vocal power from singers like Keala Settle's This is Me from The Greatest Showman

but due to its smoothness, it also losing some of note definition and edge compared to some of its competitors, let's say like monarch mkii, notes feels a bit blunted and soft on some songs, but could tame some spike from harsh old recordings

High :
a bit forward in mid treble area (8k), rolled off around 10k but rise again around 15k for extra "air" (this is one of 64's signature rise)
this gives a slight forward but smooth treble sensation that feels really open and yes i really like this treble presentation
cymbal sounds proper lacks of metallic tinge, flutes are airy and open, literally every music i hear sounds airy and open but smooth

Technical:
this iem excels in headstage and imaging yes again because of the atmospheric bass rumble + open treble, hearing orchestral and disney soundtracks feels sublime and majestic
but this iem lacks in note definition and resolution, feels kinda blunted and soft compared to some of its competitors

Comparison :
vs U12T : U12T is smoother yet much more resolving, different level of technical here no contest, but U4S sounds more exciting with that DD bass and slightly more lifted treble, personally U12T for me sounds too boring, i admit i am biased to DD bass though so this is definitely very subjective

vs Nio : i really like nio's bass, butt nio is way too thick for me, lacking sparkle on the upper frequency, that being said nio sounds more "layered" maybe due to more BA being used

vs Trio : Trio is my 2nd favorite actually having even better pinpoint imaging and resolution, it's just somehow there are some peaks around mid treble area that bothers me on some harsh recordings, also lacking module option, still like it but prefer slightly u4s during longer listening

vs M9 : M9 is always special in terms of imaging, providing one of the best laser point focus imaging i've ever tried but... it sounds more boring with thicker sound, less bass and less treble forwardness

vs IE600 : IE600 is my other favorite iem (really i am a DD lover) despite using only 1DD has better note edge and definition also cleaner in sub bass and treble attack, but the treble can be more spicy and unforgiving also has much smaller stage, and doesn't sound as "separated" as U4s

vs Mon Mkii : i never like this iem honestly, somehow not a fan of bass tuck sensation, also this iem is so much bigger than u4s, i can't wear em longer than 30 min, that being said this iem is indeed objectively good, it is more resolving, better midrange texture and definition, but yeah somehow for me doesn't sound fun enough, lacking bass fullness and impact

at the end.. simply said i really enjoy using them and it is my favorite iem beside ie600

TONALITY: 8.2/10
TECHNICALITIES: 8.6/10
CONSTRUCTION: 8.5/10
SOUND VALUE: 6.5/10

INTRO

64audio is a well known IEM company from USA. They are specialize in hybrid and multi-BAs earphones. They have alot of patented tech like the apex module (back vent tuning module) and open balanced armature among other.
Unlike some other high end IEM company like Unique Melody and Vision Ears, 64audio have a statement of ''luxurious'' IEM aimed for higher class and wealthy audio enthusiast, they don't have any IEM offered under 1000$ and today I will review their ''budget'' one call U4S.
The U4S is a 1DD+4BAs hybrid earphones, priced 1500$.

Let see in this review what worth (to me) the U4S.

CONSTRUCTION



Since these are a loaner unit from a friend, I can only comment on IEM built which is all metal. The craftmanship is good and feel sturdy. The mate blue paint is good looking too and back plate seem to be made of tempered glass. Overall look is elegant and sober.
The 2pin connectors are recessed but have no issue for usage of third party cables.
The nozzle doesn't have lip holder and is a bit problematic, I've struggle to find the proper ear tips that permit the open the soundstage but this might be IEM limitation too.
The shape isn't the most comfortable since it's quite long and tend to have the weight pulling down the IEM, so an ear hook cable is mandatory for these.



3 apex tuning module are included, and if you want the other models, it will cost you 100$ each pair, which is a bit abusive for a little piece of metal. 20$ would be a more logical price, with 15$ of profit margin.

Still, the back venting design is well done and very easy to use, its pull and push, that simple and it do inflict on bass mostly. I'm not a fan of tuning module in general.

SOUND IMPRESSIONS




Ok, firstly we have the Apex module sound tweak going on here which make the review a bit complicate but at the same time this back driver venting only drastically inflict on bass response so we can go from gently bright neutral with the MX black module to bassy L shape with the M20 silver and M15 dark grey module. For the most balanced signature, you will go with the new M12 gold module which offer a smooth neutral with slight bass boost signature and seem to achieve best of both world since bass is better controlled than M20 and M15 and not lacking rumble extension and body like the MX module.Sure, when we add bass, we add warmth too, which can densify mid range but affect negatively resolution and imaging as well as proper kick drum presence and punch, again, the M12 hit the sweet spot for me here, so this will be the one I base my review on.

Let's begin by saying the U4S aren't IEM that create wow effect but gently grow on you with their smooth yet very well resolved musicality.

The overall Tonality is neutral with slight mid bass boost to L shape with dominant sub bass while the M12 offer a balanced, smooth and near lean sounding W shape. In all case, those aren't mid centric sounding earphones, but open and mellow.

Natural, organic in balance and laid back in dynamic, the U4S are easy to love but nothing really stand apart, well, treble is the main attraction here but in a delicate way.

The fact 64audio use open balanced armature did inflict greatly on the overal tonality and timbre, it isn't an edgy sounding IEM and the definition feel a bit creamy, foggy, yet not plain blurry. We have an effortless layering and good transparency but texture is quite liquid with more attack lead definition than clean decay.

The bass is relaxed here, and offer a light warm slam that doesn't hit very hard even with bassiest module, the definition is average and separation is more about layering and bass shelf than proper clean separation. Sub bass is more boosted and the resonance can warm kick drum resolution. It's not a fast and tight bass, nor an headbanging inducing one. So, yes, a bit boring but at least not roll off. My main qualms is about the fact 64audio would be great for jazz if it wasn't of dark kick drum definition and tamed dynamic. We struggle to perceive presence properly, which lack clean definition and a bit of texture. I mean, if their no double bass or big sub bass line, kick will be thumpy enough, it's just when bass line happen that the perception will be swallowed in bass resonance.
This is a polite bass performance, with average technicalities, not very dense or vibrant, a bit thin in fact.

Mid range is more about presence than body, it's clean and transparent with impressive imaging and layering capabilities but a bit dry and thin in timbre. Yet, it's not too light in note weight and while not extremely edgy, the definition of each instrument is well resolve. We are in high fidelity, smoothed way. It's not very energic or engaging and sometime as a listenr you feel distant from center stage and mids instrument like saxophone and piano. You contemplate and open mid range instead of being part of it and the highs will tend to attire more your attention, especially percussions brilliance and sharpness.
In term of vocal, it doesn't trigger any emotionality in me, but it's clear and barely non sibilant. Female vocal are well centered, a bit compressed in presence, not wide and envolopping but quite fowards, rich in texture, very realist and never mixed up with other instrument which is good. I enjoy it but feel it lack just a hint of low harmonic warmth and timbre lushness (perhaps i prefer more colored vocal). You don't struggle to follow lyric, so we are between monitor and harman target like vocal I would say.
So for mids, upper range will be more dynamic and engaging. Violin too will have more bite, presence and clarity than densify tone, sometime it's borderline metallic sounding too, more so than female vocal which doesn't encounter as much timbral unbalance.
All in all, it's a bit technical sounding, in the sens instrument separation and attack speed is very impressive but tone will not please mid centric audiophile or those that favor tone and timbre over presence resolution. I underline this, but it doesn't mean it's clinical or artificial sounding at all, open Balanced armature avoid shoutyness as well, another plus.

Then the treble, which is both the highlight and achille's heel of the U4S. Why? Because its very good but sometime distract me from the rest of music. Its the main focus of U4S tonality, then after its the bass, and finaly mid range, this is why i struggle considering the tonal balance as U, L or W shape (well, tuning module inflict on this too). Let say the goal of U4S seem to be about delivering an effortless clarity and it's one of few DD+BAs hybrid that deliver sparkly highs....in fact, this puzzle me alot since it feel like the U4S use an EST for upper treble above 10khz where air and brilliance belong.
But this is the thing, we have a quite dominant crispness and brilliance that will extrac micro details of texture and put them fowards, sometime in plain wrong way....this make metallic percussions sounding extra metallic too, and a bit thinner than they should be but over boosted highest pitch.
But this add extra air on top and longer natural decay that we can expect from BA driver, cymbals sustain and decay is very clear and highly detailed which will sure impress those ''micro details'' seeker. Yes, the U4S are one of those IEM that reveal new sound info you weren't aware off and it's deliver in a rather delicate way, it isn't trebly or too bright at all, just perhaps a hint too spiky for perfectly rounded musical balance.


The soundstage is always dependant to source and ear tips, but don't expect gigantic out of your head spatiality with the U4S even if it's open sounding in a clean way. Wideness is just enough and feel near your head stereo way, then tallness is lower than average and feel a bit compressed, then deepness is very good and dig deep, you can travel in the soundscape too, it's not a wall of sound imposed to the listener. The center stage is a bit recessed, which explain extra deepess.

Which mean imaging is very good too, but will favor higher range instrument in term of positioning accuracy and sharpness. Yet, mid range vocal and instrument are well layered and centered too, it's not diffuse and messy in accuracy and translate spatial cue in a realist way even if not monitor like.


COMPARISON



VS UNIQUE MELODY MEXT

The Mext have a slightly similar tonal balance where we have a warm sub bass boost and crisp mids and treble, U shape way. But the Mext have a more special and magical technical performance, thanks to the wide range Bone conductio driver that permit to make the mid more fowards, transparent and detailed as well as treble notably more snappy and sharply revealing and generous in micro details, in a more effortless and fatigue free way than U4S which need more volume raising to deliver. Resolution is higher with the Mext and definition of each instrument is edgier and cleaner.
Imaging is more precise and sharp in separation where the U4S feel a bit foggy.
Soundstage is more holographic and a mix of in and out of your head experience with the Mext, while U4S is as wide but not as deep and open sounding.

All in all, technical performance is notably superior with the Mext, and we have a more engaging and revealing musicality that is less easy to forget than U4S.

CONCLUSION



My memories of the 64audio Nio are 4 years old, and it's very possible I was easier to impress at the time, still, it put the bar higher for the U4S which fail to impress me in any aspect apart coherent and well balanced tonality that is safe and easy to listen too.

For me, U4S is one more ''jack of all trades master of none'' IEM and it's hard to know wich type of audiophile will truely enjoy those. It can go from neutral to U shape with tuning module, but even with the bass boost, it doesn't trigger big fun or engagement due to a slow and warm bass response.

As well, it's hard to oversee the extremely high price for a simple 1DD+4BAs IEM, which doesn't do anything special. The fact extra tuning module cost a big 100$ is a bit of an insult too.

All in all, the 64audio U4S isn't for serious audiophile seeking high sound benefit return or TOTL technical performance and I can't suggest it to anyone that truely care about their money. You can find better IEMs under 1000$ quite easily in fact. Mangird Xenn Up or UM Mext come to mind, which offer superior technical performance.




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For more honest subjectivist (non graph based) audio review, you can give a look to my website here:
https://nobordersaudiophile.wordpress.com/

The U4s is a newcomer to 64 Audio with 4 drivers that wants to have its say in the class of IEMs around 1000 USD. This much is already revealed, that it also has features that were previously reserved for the higher-priced models.

The U4s' scope of delivery corresponds to that of the higher-end models, such as the U12t. In addition to a round leather case, it includes a silver-plated 3.5mm connection cable as well as a few sets of silicone (from SpinFit, among others) and foam tips. A balanced cable would be another cherry on top in this price range.



The build quality is, as always with 64 Audio, 1A. The blue metallic painted shells with the dark meteor design of the front panels look insanely good. Fortunately, the paint is also not sensitive and the surfaces are nice and smooth.





The U4s uses 4 drivers. A dynamic for the bass range, 2 BA drivers for the mids and a tia driver for the treble. Yes understood correctly! A dynamic driver for the bass! How much I have always wanted this for the U12t. And this dynamic driver is one of the highlights of the U4s, but more on that later.

The second highlight is the award-winning tia driver, which is used here for the treble range and was previously reserved for the more expensive models. Tia (Tubeless In-Ear Audio) is a patented IEM design method that aims to reduce unwanted resonance and distortion for a transparent and lifelike sound signature.

The U4s, like some other models, comes with Apex modules that allow for fatigue-free listening. Apex (Air Pressure Exchange) is a patented ventilation system that dissipates air pressure in a sealed ear canal, allowing you to listen comfortably for longer. This ventilation reduces listener fatigue and provides a much more realistic sound image. Each module produces a slightly different frequency response, especially in the bass. The higher the number, the more bass pressure. So the M20 module delivers the most bass, MX the least. For the very first time, an M12 module is included, which is delivered exclusively with the U4s and is located somewhere between MX and M15 in the bass range.

I used the U4s balanced with my Shanling M8 DAP. For this I used a pure silver cable from Invictus with 4.4mm Pentaconn connector. This brings a minimally better audibility than the delivery cable in unbalanced operation. By the way, due to the Linear Impedance Design (LID) the U4s does not change its frequency response and keeps it at the different output impedances of today's DAPs. Depending on the model, these vary between 2 ohms and less and no longer play such a large role in driving the U4s.



For the 64 Audio models with the longer Nozzles like the U12t or also the U4s, I basically use the JVC Spiraldots in combination with a rubber ring to create a small distance, because the Nozzles are just very long. These rubber rings are also used on PC keyboards as dampers for the keys. I basically don't use foam tips at all anymore, because they give me too closed a sound pattern. I can highly recommend the SpiralDots for the U4s, but also the included SpinFits, both of which hardly differ in sound. In terms of comfort, I find SpiralDots better, but only in combination with the rubber ring, otherwise they are a bit too flat for the U4s.

But let's finally get to the most important thing: How does it actually sound? My listening impressions were mostly made with the Apex M15 module. I tested all modules and found the M20 module to be a bit "too much" in the bass. MX sounded way too thin to me. M12 offers even better audibility, with just enough bass compared to M15. However, I feel the latter is the happy medium and the module of choice.

As I mentioned at the beginning, the bass range is the highlight of this IEM for me! It goes down really nice and deep. There is a slight emphasis in the midbass area. In terms of quantity, the U4s also satisfies bassheads and reproduces modern genres like EDM, rock, pop and metal effortlessly. I'm amazed at the bass quality paired with a great "rumble" 64 Audio puts on stage here in this price range. You have to get a Blanc out that can top that a bit. This physicality in the bass is something I've always wanted for the U12t. Not only does the bass offer this physicality, but it is also tonally very homogeneous and never blows out into other areas (unless you use the M20 module!) and always remains controlled and fast.

Tonally, we are dealing with an IEM that plays on the brighter side, but without coming across as sibilant in the upper range. It plays very dynamically and lively with resolution, where you don't miss anything at first. Only in direct comparison with a U12t or Blanc do you notice that the latter resolve the sound even finer.

In the midrange, the U4s plays more restrained than, for example, a Blanc or U12t. Voices sound further away. Instruments do not seem as corporeal as with the Blanc. This type of character makes the U4s feel fresher, more dynamic, sometimes faster than the U12t. For fast and aggressive metal I find the U4s like made or if you like it more relaxed and not directly "in your face". Since I listen to a lot of metal I have caught me during the review again and again to hear instead of 1 track of an album 3 or even 4 tracks in a row, because he simply makes a very good figure in this genre and can go down here brachial to the point, if it requires the recording. But also acts very fast and takes aggression out of the mids.

64 Audio has shown a very good hand in tuning the treble, which is probably also due to the tia driver. The highs seem very fresh and resolving and are minimally boosted a bit, which contributes to the brighter overall tuning. With the M15 module, I feel they resolve well without being annoying in the slightest. If you start the whole thing with M12 or even MX module, it can be a bit "too much" for some. Here, the bass is then properly "bounce" and the treble comes fully to the fore.

The soundstage of the U4s is exemplary. The very open presentation fans out a wide stage with very good depth imaging. Due to the slightly lower midrange, everything seems a bit deeper than on the U12t. Only in terms of instrument separation does the U12t, like the Blanc, show the limits of the U4s.

All in all, we have here again a "winner" from the house of 64 Audio, which makes the price range around 1000 USD all honors. Just consider the technologies used in this model, which have been developed by 64 Audio in recent years and are used in the much more expensive models. Tia, Apex, LID, and even the four-way crossover, which reduces distortion in the lower frequency range through the use of a proprietary electronic low-pass filter.

Overall, it's amazing how close this U4s comes to a U12t and even beats it in parts. I find the bass of the dynamic driver superior to that of the BA driver in the U12t. The U4s stalks a Trio quite closely, only acting a bit fuller and more natural in the midrange as well as offering more resolution, otherwise they are almost on par. Personally, I like the somewhat restrained midrange as a counterpart to my Blanc. This reminds me of my 1266 Abyss TC, which is also known for being one of the best metal headphones of all time. And this has, as is well known, also a slightly recessed midrange, in order to be able to reproduce more aggressive music a little more relaxed.

From me, the U4s gets a clear recommendation!