64 Audio U18s Universal-Fit Earphones

I confess: I have never seen in real life a balanced armature driver. Oh, I’ve used plenty of IEMs which employ them, but of course the BA drivers are hidden inside. I knew they must be small, seeing as how many IEMs use several in one earbud. But I don’t think I realised how small.

See the photograph above? What you’ll see is a Rubik’s cube, which I use (except when I forget) to establish the scale of the various things I’m reviewing. Atop that is one 64 Audio U18s earphone. I’ve disconnected it from the cable and removed the tip. In that state it weighs just 8.2 grams. It’s a little larger, I’d say, than the typical IEM earpiece, but not by much.

Now understand this: inside that earphone are eighteen balanced armature drivers. Eight of them are for bass, eight for lower midrange, two for upper midrange and one for high frequencies.

Let’s explore these marvels of miniaturisation further.

64 Audio U18s Universal-Fit Earphones


  • The 64 Audio U18s earphones are wired earphones packing eighteen balanced armature drivers in each earbud. Eighteen!
  • They feature CNC machined aluminium bodies, sand blasted, fly cut and twice anodised
  • Made in the USA
  • Eight of the BA drivers are for bass, eight for midrange, one for high-mid frequencies, and one for high frequencies alone
  • High frequency driver employs “tia” tubeless design (the tube is the section emitting the sound from the balanced armature “box”), designed to reduce resonances
  • 10 to 20,000 hertz rated frequency response
  • 106dB/mW rated sensitivity
  • 8 ohms nominal impedance
  • 4-way passive crossover network, designed for linear impedance
  • Three sets of “apex” plugs which provide different isolation from external sounds and also tailor bass performance
  • Three sizes of silicone ear tips, three sizes of TrueFidelity ear tips, three sizes of memory foam ear tips
  • 2 grams each (disconnected, with no tip fitted)
  • Removable 1.25 metre cable; 3.5mm single ended plug at source end, seemingly proprietary two prong connectors at earphone end
  • Hard carry case included
  • No instructions included
  • Detailed and exceptionally clear sound performance, with a tilt towards upper midrange emphasis in what seems to be the 64 Audio house style.
  • Price: $4399
  • Available at fine high fidelity retail outlets, and direct from distributor's retail division here
64 Audio U18s Universal-Fit Earphones

    More about the 64 Audio U18s IEMs

    I do have one significant complaint about these earphones, as I did with the 64 Audio Nio IEMs which I reviewed a little while back: they lack any kind of documentation at all.

    Earphones, you might say, don’t need documentation. I suppose so, except that these ones have a unique feature which requires the user to make a choice. A little guidance would be useful. I’m not sure why a slip of paper couldn’t have been included providing that guidance.

    The unique feature as that these earphones are provided with vents for the bass drivers. That is, they can breathe. How much they breathe depends on which of three “apex” plugs you insert into the small holes on each of the earbuds.

     “Apex” stands for Air Pressure eXchange. Each of the plugs provides a different level of acoustic isolation from the outside world and loading on the bass drivers. Each plug is a small, seemingly aluminium cylinder with two O-rings for sealing. Each has a couple of port slots on the section which protrudes slightly out of the body of the IEMs. Inside there is apparently a different degree of damping materials affecting the transmission of sound between each earphone and the outside world. That affects both the amount of outside sound that they permit to pass through to your ears, and also the bass power provided by the dynamic driver. The pre-installed ones are M15 models, which stands for 15 decibels of outside-noise reduction. The others were MX, for 10dB of isolation, and M20 for 20dB.

    64 Audio U18s Universal-Fit Earphones

    64 Audio says that this system provides a “pneumatically interactive vent that relieves pressure and reduces ear fatigue.”

    The single high frequency balanced armature driver uses a “tubeless” design. The idea is that the tube on the end of the balanced armature driver is truncated, or perhaps completely omitted, to provide a more direct feed of those frequencies. 64 Audio says that this design “eliminates resonance providing optimal clarity”.

    The bodies of the IEMs are machined aluminium – “fly cut” says 64 Audio. I had to look that one up. It’s a milling process with a cutting tool on a rapidly rotating disk. Apparently it’s ideal for providing an extremely smooth result. These earphones certainly looked very handsome to my eye, without being at all ostentatious. If your aim is to flaunt expensive earphones, they are perhaps a touch too tasteful for that.

    The cable is eight-braid silver. It also is handsome, and the 90-degree metal – is it brass, or gold-plating? – 3.5mm plug is as well.

    There are lots of eartips included, along with a rigid carry case.

    64 Audio U18s Universal-Fit Earphones

    Listening with the 64 Audio U18s IEMs

    I started out with the largest size of the memory foam tips on the earphones, but after a while switched over to the mid-sized ones. These seemed to give a better seal with my ears. For the most part I used the excellent Astell&Kern A&futura SE180 digital audio player (review here), but also played with the Topping A90 desktop headphone amplifier, as well as the iFi Audio ZEN CAN headphone amplifier.

    The initial overall impression was good tonal balance with, perhaps, a slight emphasis on the upper midrange and a slight diminution of the bass. I emphasise slight in both cases.

    I started with a high-definition remaster of Jethro Tull’s Thick as a Brick. There was superb clarity and with a decent thump of the kick drum, with a relaxed, easy-to-follow bass line. Again, the bass seemed very slightly recessed compared to most gear I typically use … and then I discovered something. It turned out that I had the EQ switched on with the SE180. It was set to the “Normal” preset. I have no idea what that’s supposed to do, although you’d think it flat. I think it was supposed to be, but it also dragged down the overall level by at least six decibels, presumably to allow headroom for the boosting of chosen frequencies. But switching EQ off completely changed the character of the sound enormously.

    64 Audio U18s Universal-Fit Earphones apex modules and tips

    There was still a slight pinching – emphasis on the upper nasal tone – in Ian Anderson’s voice, but that apart the 64 Audio U18s earbuds delivered a superb clarity. When the rockier part kicks in around three minutes into the song, the drum patterns were delivered in a really rather exciting way, and the sound stage was open, yet cohesive. There was no apparent dynamic compression. Everything was simply there. Five minutes in when the flute starts up, there’s some beautifully rendered tambourine in the left channel, lifted a little above the rest of the instruments, but slightly distant with a fine sense of air. I highlight that just as a single example of the kind of thing that abounded through this listening session.

    Over a week or so during which the 64 Audio U18s IEMs were plugged into my ears for a significant period, I found no music that essentially differed in its delivery over these earphones. Detailed, that slight upper midrange emphasis, and a bass that I gradually came to view not as slightly recessed, but rather more accurate than delivered by a lot of gear. In other words, its relative restraint was, from the point of view of accurate reproduction, a virtue.

    64 Audio U18s Universal-Fit Earphones

    Initially the different Apex modules seemed to make rather less of a difference to the sound than what I’d experienced with the 64 Audio Nio IEMs. Indeed, as I was switching between them, I paused for a while with no modules at all inserted – thereby allowing the IEMs to vent freely into the surrounding air. The bass was barely affected. But that was with the 1980 Rush album Permanent Waves, which really doesn’t have much very deep bass. When I switched over the Billie Eilish’s When We All Fall Asleep, Where Do We Go things were very different. Listening module-free clearly knocked quite a few decibels off the lowest octave. Still, the difference between the modules was modest.

    And finally, it’s perhaps a little strange to consider using earphones in this price range with a mere iPhone, but I’m of the school that if your choice is between an iPhone with music, and no music at all, I’ll go for the iPhone. And, yes, these earphones delivered fine sound at respectably high volume levels, even powered by an Apple Lightning adapter.


    The nominal impedance is quite low for earphones – just eight ohms. One of the features 64 Audio highlights it calls LID, for Linear Impedance Design. It explains that LID “corrects the non-linear impedances of the drivers, restoring proper interaction with the source and preserving the desired sound signature.” It doesn’t go into technical details, but I take from the name and description that it aims for an even impedance across the frequency spectrum.

    Well, my measurement supports that. Running a test across the frequency spectrum via a 466-ohm inline load, the resulting variation in input signal was less than 3dB, thus:

    64 Audio U18s Universal-Fit Earphones impedance graph

    That means with the sub-5-ohm output impedance of the gear these earphones are more likely to encounter, you can expect an input signal variation of less than 0.3dB, and with quality audiophile gear, well under 0.1dB.

    That’s a pretty impressive achievement given the four-way crossover and the eighteen drivers.

    A more detailed explanation of this measurement and the importance of it is here.


    There was a family resemblance to the sound of the 64 Audio Nio which I’ve previously described as slightly idiosyncratic. All decent headphones, and even more so for in-ear gear, involves a lot of artful judgement by their designers to produce a natural sound. And that will inevitably differ from designer to designer, not just in their judgement but according to how things sound to them. It’s clear that Vitaliy Belonozhko, the Founder and Chief Sound Designer of 64 Audio, has a definite vision for how IEMs should sound. And it’s clear that he can achieve that vision.

    And that the 64 Audio U18s earphones are one of the highest realisations of that vision.

    64 audioIn-ear earphones