Introduction

64 Audio is one of the most established brands when it comes to in-ear monitors, so much so that its IEMs are actually used for monitoring music live on stage by performers including Beyonce, Jay-Z, John Mayer, IU, Bon Jovi, and many, many more. This reputation has been well-earned for its custom IEMs thus, although most audiophiles who have listened to 64 Audio universal-fit IEMs, or UIEMs, profess they sound even better! Indeed, we took a look at its co-flagship U18t which fits all of 18 balanced armature drivers in a relatively small and comfortable shell for one of the most detailed audio reproductions I've experienced, and that was followed up by the 64 Audio Duo that aimed to address the new normal of working from home and also being on the go where an open-back set of IEMs helps maintain more awareness of your surroundings while still enjoying your music. To say both of these are on the more experimental side of 64 Audio's product line would be a fair statement, and today we take a look at something that has me quite excited given its potential to be a strong contender for both professionals and audiophiles alike.


When this review goes live, 64 Audio will have announced its latest and least-expensive-to-date UIEMs called the U4s. This is a universal-fit version of the 64 Audio A4s, a CIEM released in 2021 that is interesting in its own way but is best treated as a separate product. The new 64 Audio U4s does share the same driver platform as the A4s in being a hybrid driver set of IEMs using a dynamic driver and three balanced armature drivers. There's been something about the resurgence of these low driver count IEMs in the kilobuck range which has helped show that the driver count and driver type is not as important as the driver implementation itself. Indeed, one of these BA drivers is the excellent 64 Audio Tia (tubeless in-ear) driver which I've appreciated for adding air to instruments in the higher frequencies. Then there is the part where the U4s is compatible with 64 Audio's Apex modules which allow for different levels of isolation and bass response while improving user comfort. The U4s releases with a brand new set of m12 Apex modules which the company believes is a great fit with these IEMs too. There's clearly a lot to unpack and test here so let's thank 64 Audio for providing a review sample to TechPowerUp and begin this review with a look at the product specifications in the table below.

Specifications