The 64 Audio U4s is the current darling of the high end in-ear monitor (IEM) world. Given 64 Audio’s track record of producing excellent IEMs and an entry-kilobuck price tag of $1,099, the U4s was sure to turn heads. My friend Precogvision wrote an excellent review article here on release day that answered the most important question: yes, it’s good. Very good.
In particular was the line:
You might imagine my surprise to finally hear the U4s and find it to be pretty much everything the Nio was - and possibly more.
From my own journey through the 64 Audio line-up, the $1,699 Nio was one of my favorite IEMs and a strong contender for the IEM I would buy myself. So for the U4s to potentially be a better, cheaper Nio, I knew I had to listen. Here are my impressions of both.
Shoutout to Bay Bloor Radio in Toronto for the opportunity to demo these IEMs and more.
Note that this is an impressions article, not a full review. An expanded “first look” rather than an in-depth analysis conducted over multiple days and dozens of listening hours. It will give you a good idea of my initial thoughts on these products but these may be subject to change with further ear time.
Build and Fit
The U4s has the same build as the Nio, U6t, and U12t, and U18s. 64 Audio found a design that works with all their products and have continued to carry it through to the U4s. It’s well-built and comfortable, especially with the APEX modules that help regulate in-ear pressure. Personally, while I like the U4s’ cobalt blue metal shell, its dark “meteorite” faceplate isn’t as appealing as the Nio’s pearlescent aesthetic.
The U4s’ driver setup runs a 1 DD + 3 BA configuration that features all of 64 Audio’s innovative IEM technologies. This is in contrast to the Nio’s 1 DD + 8 BAs. The other important difference is the inclusion of a new APEX module, the m12, that attenuates bass to a level that’s between the mX and m15 modules. For this comparison, I used the standard m15 module.
I can confirm that Precogvision is right in his valuation. The U4s and Nio sound very similar to one another. The U4s is, at worst, equal to the Nio and at best, just a tad superior. Given that you’re saving $600 going for the U4s over the Nio, it’s very hard to justify buying a new Nio in today’s market. But for the sake of comparison, let me walk you through what I’ve discovered. Maybe these tiny nuances will make all the difference for you.
The Nio’s overall tuning can be described as an L-shape. A gobsmacking amount of bass, relaxed mids, and a darker (though not deficient) upper treble. The U4s is more akin to a U-shaped signature. The primary differentiator is having quite a bit more upper treble zing. This treble emphasis isn’t what I would call treble brilliance - that is, a clean, clear accentuation that effortlessly captures and highlights the complexities of the hats and cymbals and similarly delicate notes. Rather, the U4s’ treble is saying “Hey, don’t forget about me!” as it brings more of it into the foreground. In contrast, the Nio’s treble is content to hang backstage and play a supplementary role. If you’re comparing them directly back-to-back, it can seem like the U4s is effectively exaggerating the treble of the Nio. But to be honest, I didn’t really notice this in my first listening session just with the U4s alone. It was after I went back to the shop a few days later to purposefully compare it against the Nio that it was apparent.
Frequency response comparison between the 64 Audio U4s and Nio. Courtesy of Precogvision.
The bass of these two IEMs is a toss-up. It’s a bit hard to tell which I prefer, though I suppose I would lean ever-so-slightly towards the U4s. The best way I can describe it is through how it renders instruments. With the Nio, my attention is drawn to the drums, their weight and impact as they land, the oomph and boom as the dynamic driver pounds away. With the U4s, I instead noticed the foundational synth and bass lines. In essence, the U4s tightens the transients enough that I better appreciated the more discrete instruments in a passage. The Nio has an element of that overly indulgent “dirty bass” cliche while the U4s spares some of its focus on articulation. That isn’t to say the U4s doesn’t bring justice to the drums. It still delivers with a sense of weight and decay, maybe a little more realistically than the extravagant Nio. But as with the treble, these differences are minor. I had a harder time figuring out the nuances between the U4s and Nio’s bass compared to the treble and mids.
Speaking of the mids, the Nio’s midrange is a bit thicker than the U4s as a result of having a little less pinna gain and more lower mids/bass. What I like about the Nio’s midrange performance is how comparatively smoother its vocals are. Electric guitars also highlight this discrepancy. The scream and grittiness of the electric guitars stand out on the U4s. We can get a hint of why this is the case on the frequency response graph; that 2 kHz peak in the U4s over the Nio brings forward that electric guitar energy, while the lack of it on the Nio mellows out the vocals and eliminates any semblance of harshness. I slightly prefer the Nio’s midrange as a whole but I do miss some of that electric guitar grit at times.
On a technical level, I didn’t really note any significant deviations in the time I had. Soundstage, imaging, and resolution were essentially the same. Though at times when I thought I might have heard a difference, switching back and forth made me concede that I couldn’t pinpoint anything. In other words, the difference is so negligible that even comparing them side-by-side, I couldn’t distinguish it. Rest assured, I doubt anyone buying just one will somehow be missing out. Perhaps if I did a full dedicated review between them I’d be able to tell. But let me remind you that the Nio is over 50% more expensive than the U4s. The diminishing returns here are real.
“If you don’t cannibalize yourself, someone else will.” This was one of Steve Jobs’ most memorable quotes and it’s an apt description of what 64 Audio has done here. I simply can’t justify getting a Nio when the U4s exists. It’s still not the perfect 64 Audio IEM for me, as I would ultimately prefer a tonal mix between the two. It’s also still a clear step below the technical champion that is the U12t. But for its asking price of $1,099, the U4s has solidified itself as one of the foremost contenders for the kilobuck crown in my eyes.