Closer Examination

Adding to the similarities with the U18t is the inclusion of the same 64 Audio Premium Cable which costs $199 by itself. It starts with a straight 3.5 mm TRS connector for your source, and notice that the housing is all aluminium with the 64 Audio logo on it. The 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. There is a section of translucent plastic sheathing over the cable closer to the other end, which is pre-formed into a hook that go over and around the back of your ear. Angled connector housings come marked "L" or "R" for the left and right channels respectively. The physical connectors 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. Modular plugs on the source end would have been nice at this price, or even black nickel-coating instead of gold for a stealthy black look, but this remains a good cable with a rated net impedance of 0.23 Ω and measured electrical resistance of just under 0.30 Ω from end to end. I have seen plenty of better-behaving and looking cables for the money though, including from the likes of DUNU and Effect Audio that only only do modular plugs but are easier to shape and don't kink at all, so this is not a cable I would buy separately, though it is plenty satisfactory as an inclusion in the box.


Let me state right off the bat that the 64 Audio Duo is smaller than all photos and videos online make it seem. In fact, I am not even convinced my own photos do any better, and this has a lot to do with the various elements that come together in making these IEMs. Not much detail is available about it online, but a first-party YouTube video confirmed that the shells are milled out of a solid piece of 6063 aluminium alloy. They are given a semi-custom fit to ergonomically fit into ear conchas and have a matte black anodized finish for durability and resistance to fingerprints and finger oils. The face plate, if you will, consists of an aluminium plate as a base that wraps around the sides via an added stainless steel bezel trim. A perforated 304 stainless steel grille insert with a black PVD coating makes the Duo one of the most open IEM sets I have ever handled to date, which has air freely flow in and out while still protecting the drivers inside. The black, silver, and black color scheme is one of the most striking implementations of the monochrome colorway too, with the Duo still coming off as a purposefully non-flashy design that can be worn in public as much as on a Zoom call screen.


Here is a closer look at the complex 3-piece face-plate design on the 64 Audio Duo. It shows that the chromed plate is a slotted base for the perforated grille insert, too. We even get a sneak peek at the internal wiring connecting the cable connector to the drivers, which clearly shows that this is an open set with minimal airflow restriction from the grille and slotted plate underneath aiming to provide a controlled seal, and thus bass extension. This is what 64 Audio calls its Apex Core technology, and it is the Apex modules technology we saw in the U18t, but taken further and laid down to the core. The closest analogy I can think of to better relate this to TPU readers is a honeycomb mesh on PC case panels and PSUs which is not as restrictive as a mesh filter and still open enough for practically unimpeded airflow. But as if this were not enough, there is a dedicated vent on the sides for air to move through fully. The side profile shows the integrated cable connector that slightly juts out past the shell walls surrounding it, and it is otherwise flush with the cable when connected. The inner side touching the ear concha has a truncated 64 Audio logo, L/R markings for the left and right channels, and model name and serial number, albeit without the demo markings on mine. The ear tips go over a relatively thin and long nozzle shaped deliberately to accommodate the tia driver, and there is no notch that would otherwise help keep the ear tips in place once installed. The nozzle also isn't angled inward aggressively, but its length should help with the fit, as will the thinner shells. A metal mesh filter placed on the nozzle opening prevents contaminants from entering the acoustic chamber, and given their uncommon size, I would have liked 64 Audio to provide some replacement filters in the box.


Fitting the ear tips is easy because of the relatively small diameter nozzle. It is <=5 mm at the widest point, which the ear-tip bores push through easily enough. Seen above are the foam and two size M silicone ear tips installed on one of the IEMs to show the length and form factor of each. The all-black 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. You may want to try different ear tips to get the best-possible fit, and perhaps affect the sound signature with the foam instead of silicone tips. Certainly also try out different sizes to ensure you have them on properly, and do not feel as though both ears necessarily need the same-sized ear tips, either. Regardless of which tips you go with, the next step is to re-connect the cable by carefully identifying the matching channels and orienting the ear hooks around your ears when connected to the IEMs. Doing so is extremely simple since you just push the male plugs into the female ones on the IEMs, which are then held there by friction alone. Now simply connect to the source using the 3.5 mm TRS connector on the other end of the cable. I know there are many who prefer using IEMs throughout, but I like to use over-ear headphones when sitting down and IEMs on the go. I paired the 64 Audio Duo with all the tested portable DAC/amps I have to date and personally like the cleaner profile and handy EQ options of the Qudelix-5K as the source, in turn paired to my phone or laptop.