64 Audio U4s Review

by: Gabby Bloch
  | Press Ctrl+D to bookmark this page Link copied to clipboard

64 Audio U4s Review

A few years ago, 64 Audio may have been considered to be one the most expensive IEM brands on the market. But boy, times have changed. It seems that many trendy IEM companies have arbitrarily raised their prices on their latest models by a significant amount. So, it was refreshing to see 64 Audio come up with another reasonably affordable IEM, the U4s. How does it compare to other IEMs in the $1000 price range? And does it live up to 64 Audio’s high standards?

In the Box

  • U4s In-Ear Monitors
    Detachable Cable with 3.5mm Termination
  • 64 Audio Hard Case
  • Silicone and foam ear tips
    Cleaning Tool
    Shirt Clip
    apex Modules
  • Product Manual

64 Audio U4s Review: What's in the box

Look and Feel

64 Audio designs its universal IEMs in a pretty uniform fashion. The shells tend to be compact compared to the more bulbous shapes of other high-end IEMs. This makes them appear simple, yet elegant. The aluminum blue along with the shiny black and silver marble face certainly have an aesthetic appeal. In fact, they might my favorite universal 64 Audio IEM in terms of appearance. Finally, the small, elevated circular “vents” on the shell are their “apex” technology, which we will discuss in the design section below.

The fit is certainly comfortable, but like all 64 Audio IEMs, the seal isn’t extremely tight. In fact, if you try to push them in too snugly, you might lose some bass presence. These earbuds are designed to be fatigue free in every way (more about that below). Still, they feel very secure in the ear, and are comfortable even throughout long listening sessions.

64 Audio U4s Review: IEM shell size


The U4s is designed with 4 drivers - one dynamic, two balanced-armatures, and one patented tia driver. It employs a four-way crossover that boasts an electronic low-pass filter, which helps to reduce low-frequency distortion.

One major design element to note is the “Apex” technology (Air Pressure Exchange), which is a patented vent that releases air pressure in the ear canal, thus reducing any fatigue during listening sessions. The Apex design also contributes to a more spacious soundstage, and even allows you to adjust the tuning by including 4 module variations (think of them as sound filters). For this review, I used the m12 apex module, which is the “default” tuning setting.

The U4s is easy to drive with a low impedance of 11 Ohms and sensitivity of 107 dB. Since the included cable has an unbalanced 3.5mm termination, I paired it with my trusty Dragonfly Cobalt DAC.

64 Audio U4s Review: Apex technology

Sound Impressions


The first thing that stands out  is the significant height of the stage. At times, it even feels like the placement, though notably nuanced, almost artificially elevated. But this in no way detracted from the enjoyment of the listening experience; if anything, it enhanced it. The sense of depth is less pronounced, with imaging tending to fall on the vertical and stereo field. The scale is not exceptionally expansive, but with the separation between instruments being so well-defined, I never felt hungry for any contrived spaciousness. And in this respect, the soundstage is ultra realistic and accurate.


The U4s presents a powerful, yet clean low-end. 64 Audio has skillfully balanced the tuning in this range, giving relatively strong presence in the sub-bass and lower-bass regions. But as it creeps up this range, the bass tempers a bit. As a result, there’s as tidy separation between the low-end and the mids. So, while you get appropriate oomph when listening to pop and hip-hop tracks, there’s never any hint of muddiness or bloat. The low-end profile also lends itself beautifully to acoustic genres, like jazz and classical, offering an incredibly natural and unsaturated tone to double basses and cellos. And to be honest, I have rarely heard acoustic instruments this textured and transparent on an IEM at this price point. The level of detail is $2K good.


Although the balance is tasteful in this range, the upper-mids take precedence over the flattened lower mids. Again, this makes for a clean sound, but there’s less sense of fullness and body as a result. On the flip side, there’s some lively snap when percussion hits the upper half of this range, giving a driving energy to the track. And although vocals protrude a little in the upper-mids, the balance stops shorts of creating any harshness. The separation is superb on the U4s, giving guitars precise definition while also managing to delicately handle the instruments with certain level of tenderness. And this is quite a feat considering there is no added color or artificial softness to the timbre.


Although there is emphasis in the upper treble, there is never any piercing quality. Yes, violins and brass will poke through a little in the higher part of this range, but the sound moves through the peaks with smoothness. Female vocals are pleasure to listen to in this range, offering that famous 64 Audio air and lightness that characterizes their sound signature. And again, the U4s's transparency is top-notch, while at the same time maintaining a feeling of fluidity.


Although the exceptional level of precision and lack of significant coloration would suggest an almost clinical profile, the U4s is far from boring. The powerful lower-bass frequencies along with the spirited upper mids and high-treble give tracks a lively, yet controlled energy. Add to that a level of resolution that surpasses any other earbuds at this price point, and you’ve got one of the best performing IEMs on the market for under $1500. Some may prefer a warmer and richer profile than what the U4s presents. Certainly, it retains some elements of the 64 Audio “neutrality” that the brand is known for. But there’s no doubt that the U4s is one highly talented IEM.

You can buy the 64 Audio U4s at Audio 46.

64 Audio U4s Review: Specifications


Transducer Type

Dynamic & Balanced Armature

Transducer Configuration

1 dynamic low, 1 BA low-mid, 1 BA high-mid, 1 tia high

Bore Configuration


Frequency Response

10Hz – 20kHz


107 dB/mW (94mV) @ 1kHz


11Ω @ 1kHz


Integrated 4-way passive crossover

Get the Latest Headphone News and Reviews in Your Inbox

Leave a comment

Please note, comments must be approved before they are published


Your cart

Trouble with payment options in checkout?


Go through checkout faster with our Express Checkout options: