Closer Examination

The cable that ships with the 64 Audio U4s is the company's $199 Premium Cable in black. It's the same cable that I have used in the past with the U18t and Duo, although I had to double check because this one felt a lot more supple and less prone to kinking than before. I am not sure if the sheathing material is the same or perhaps even from a different manufacturing batch, but it does help address one of the issues I had with a cable that costs more than some less expensive and modular offerings from China. This is a single-ended cable starting with a straight 3.5 mm TRS connector from your source that is tied to an aluminium housing with the 64 Audio logo on it. The cable conductor is 26 AWG thick silver-plated OCC (Ohno Continuous Cast) high-purity copper braided into four strands that employ a 7x7 multi-twist each. It's a predominantly black cable down to the branded cable splitter and cinch, which works well in containing the two split lengths at any specific point because of the tapered structure. Closer to the other side we see pre-formed ear hooks that help make the cable go over and around the back of your ears. The cable terminates in two angled plastic connector housings which are marked L/R to help identify the left and right channels, respectively. The connectors themselves are standard 0.78 mm 2-pin plugs, and these are gold-plated for oxidation resistance as with the 3.5 mm plug on the other side.


Anyone remotely familiar with 64 Audio IEMs already knows to expect an ergonomically shaped shell and the same continues with the new U4s. This universal-fit set also follows up on the design language used on other U-series IEMs in using a CNC-machined aluminium composition that is then anodized for aesthetics and durability alike. The U4s gets a "Slate Blue" color which is seemingly inspired by some of the "world's most beautiful blue-dial timepieces" in 64 Audio's words. In practice, I quite like the deep blue finish that also has slight iridescence in that the actual hue appears to vary from lighter blue to a darker one depending on the incident light and the viewing angle. The shells are on the smaller side of average and this should aid in achieving a comfortable, secure fit in the ears.


A closer look at the face plates reveals a resin cover over a design that feels abstract at first, but then it reminded me of some of the meteorite samples I have. As it turns out, 64 Audio took inspiration from the famous Muonionalusta meteorite, and you do need to see it in person to better appreciate it. Overall I'd say the U4s is still on the stealthier side compared to what the IEM market is going through these days with some sets looking more like ear jewelry than earphones. Below the face plate we find the pre-installed m15 Apex module which has notches on the side to help you remove it. This in turn reveals a vent that these Apex modules help release air pressure from the otherwise sealed ear canals the IEMs fit into—hence the term Apex, which is short for Air Pressure Exchange. With the new m12 module, the U4s now comes with four sets of Apex modules that isolate to different levels simply by controlling the extent of this venting. Going left to right in the photos above, we have the silver m20, the gray m15, the new gold m12, and the black mX (X for 10) where the numbers correspond to the isolation provided in dB. As such, the U4s with m20 modules would be the most isolating and provide the most bass response in theory. The dual O-rings help with a secure fit while preventing debris build-up in use. Just be aware that the new m12 modules do clash with the more subtle design of the U4s, at least in my opinion.


A look from the side shows the two-piece construction for the shells although there isn't really a gap per se here, in that you don't have to worry about dust getting inside. The lower (inner) section is also machined to allow for the cable connectors extending out the side where the shell enclosure could have been a tighter fit. The inner surface contacting the ear has L/R markings, if you need it, in addition to the model name and serial number itself. The side is primarily flat before having an indent leading up to the thin and long nozzle and there isn't a notch on either end to keep the ear tips in place once installed. The nozzle also isn't very aggressively angled inward, but its length should help with the fit. A metal mesh filter placed on the nozzle opening prevents contaminants from entering the acoustic chamber, and given the uncommon size, I would have liked 64 Audio to provide some replacement filters in the box.


Fitting the different ear tips is easy because of the relatively small diameter nozzle that is ~5 mm at the widest point, which the ear tip bores go around easily enough. Seen above are the foam and two silicone ear tips in size M, installed on one of the IEMs to show the length and form factor of each. The all-black wide bore silicone tips turned out to be my favorite of the set overall, and we can see how the nozzle is nearly flush with the bore opening there as well. Do try the various provided options here to get the best possible fit, and perhaps also affect the sound signature slightly, and keep in mind that both ear canals don't need to have the best seal with the same size or set, either. Regardless of which tips you pick, the next step is to re-connect the cable by carefully identifying the matching channels and orienting the ear hooks around your ear when connecting the IEMs. Doing so is simple, as you just push the 2-pin connectors in place and they remain there via a friction fit. Note the connectors on the cable not going into any recessed housings on the IEMs, so they do jut out slightly and take away from the otherwise excellent aesthetics. The 3.5 mm connection then heads to the source where, given I found myself using this set on the go as well as lounging around in the living room, a good portable DAC/amp such as the Questyle M15 or the overkill FiiO Q7 came in quite handy.