Published On: September 18, 2021

64 Audio U6t Universal In-Ear Monitor Review

Published On: September 18, 2021
Last Updated on: October 30, 2021
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64 Audio U6t Universal In-Ear Monitor Review

The U6t in-ear monitor brings the sonic performance of 64 Audio’s A6t into a universal option that a broad spectrum of consumers can utilize.

64 Audio U6t Universal In-Ear Monitor Review

  • Steven Stone is the former editor of He a longtime audiophile and home theater writer, as well as a musician and recording engineer. Steven has written for publications like Stereophile, as well as,, and The Absolute Sound.
    Steven is plays guitar, mandolin, and Ashbory bass and is a collector of fine musical instruments.

64 Audio ranks as one of the leading manufacturers of custom-formed in-ear monitors for performers and serious listeners. One of its most popular models is the A6t six-driver per earpiece custom in-ear monitor (starting at $1299 MSRP). The newest model, the U6t ($1299 MSRP), makes the same technology available in a universal fit monitor.

The U6t is 64 Audio’s least expensive universal-fit offering yet. According to Vitaliy Belonozhko, 64 Audio’s founder and chief sound designer, “The U6t represents the culmination of some very hard work by our R&D and engineering teams to bring the A6t’s sonic performance into a universal option that can be utilized by a broad spectrum of consumers who can now experience 64 Audio’s technologies that were previously relegated to our higher-end and more expensive custom monitors.”

Main Features

The U6t utilizes six balanced armature drivers with one high, one high-mid, two mid, and two low-frequency drivers. With a sensitivity of 108 dB at 1 mW and an impedance of 10 ohms, the U6t easily powers to satisfying levels even with a smartphone. The crossover is “four-way passive,” which means all the drivers can roll off naturally without additional attenuation at the frequency extremes. If done well, this method produces an extremely transparent result.

There are usually fewer issues with phase shift at the crossover regions with a passive crossover scheme. Still, it depends on the quality of the drivers and the designer’s ability to source six drivers that will integrate natively.

Tubeless Internal and Linear Impedance Design

Many multi-driver in-ear monitors utilize small tubes to direct the output of each balanced armature driver to the earphone’s tips. 64 Audio takes a different approach. Its tubeless design, which it calls tiaTM technology, is exclusive to 64. It includes two major elements: the tia high driver and the tia single bore design.

According to 64 Audio, “the sound produced by the tia system can disperse freely and effortlessly, yielding an incredibly smooth musical frequency response.”

The tia system works in tandem with LID™ (Linear Impedance Design), also exclusive to 64 Audio. It’s a proprietary circuit that corrects the non-linear impedance of the drivers. According to 64 Audio, “it restores proper interaction with the source, preserving the desired sound signature.”

Air Pressure Exchange

One of the primary complaints with in-ear monitors, if they are entirely sealed with full occlusion - necessary if you want to hear the correct frequency response - bass frequencies can cause excess pressure in your ear canals. 64 Audio’s patented Air Pressure Exchange (apex) is a pneumatically interactive vent system that releases air pressure in a sealed ear canal.

All of 64 Audio’s current IEMs have the apex technology. Some, including the U6t, come with three insert options (mX, m15, and m20). According to the brand, “Unlike competitor venting solutions, apex preserves the bass frequencies and produces a more open soundstage, which helps the listener distinguish individual instruments. The apex module is also engineered with features to prevent vent-clogging and wind noise.”

The U6t has three sets of interchangeable apex technology inserts that deliver different levels of outside noise attenuation. You have the option of three levels of isolation provided by apex, -20dB (m20), -15dB (m15), and -10dB (mX). According to 64 Audio, “The m15 allows for slightly more ambient sound than the m20 and helps temper the bass. The mX reduces the ambient noise isolation to only -10dB, but in return transforms the earphones into a master-grade tool with a resolved sound signature.”

Capsule and Cable Design

While 64 Audio’s custom in-ear monitors utilize a shell that is 3D printed hypoallergenic acrylic material, the U6t has a metal housing. The metal housing ensures that the balanced armature drivers inside are well protected from trauma. The cable with the U6t is a 4 Multi-Twist Silver Plated OCC Copper Wire 26 Awg with only 0.23 Ohms of total impedance. Unlike many in-ear monitors with mediocre cabling, the U6t’s cable is better than many aftermarket cables in strength, flexibility, and overall ergonomic style.


64 Audio U6t Universal In-Ear Monitor Review - Lifestyle

Your comfort level with the U6t depends on how well they fit your ear canal openings. While it doesn't require a deep insertion, as with Etymotics, it needs to be seated well enough for a complete seal. The U6t comes with a good selection of ear tips, and I strongly suggest trying them all to see which one is optimal for you.

In-ear fit is a personal thing. For me, the U6t was a mixed bag. Due to its weight and size, I found that even with the foam tips that delivered the best fit, I needed to reseat the U6ts periodically as they lost seal over time.

While I have not tried the custom version of the U6t, the A6t, if you love the sound of the U6t, you might want to move to the A6t for added comfort.

What’s in the box?

64 Audio U6t Universal In-Ear Monitor Review - Box

Inside 64 Audio's circular black faux leather box, you will find:

  • A pair of U6t Universal In-Ear Monitors
  • TrueFidelity Eartips in three sizes (S, M, L)
  • Silicone Eartips in three sizes (S, M, L)
  • SpinFit Eartips in three sizes (S, M, L)
  • 64 Audio's Black Premium Cable
  • m20 apex Modules for 20 dB isolation
  • mX apex Modules for 10 dB isolation
  • m15 apex Modules for 15 dB isolation
  • A 64 Audio round sticker for your locker room door. 

How Do the U6ts Sound with Music?

Acoustic/Quiet Music Performance

"Blue in Green" – Miles Davis

The soft brushwork and the bowed bass come through with excellent clarity and transparency. The U6t in-ears do an excellent job of letting the micro-dynamics of Miles' solos come through unfettered.


Rock/Loud and Fast Music Performance

"Boilermaker" - Royal Blood

The U6ts lets all the slam and bluster of this boisterous tune penetrate your cranium. If you like nasty, hard-hitting metallic guitar coupled with sledgehammer bass, this cut is for you. The U6ts have no problems handling this aural barrage.

Royal Blood - Boilermaker (Official Video)

Bass Heavy/Pop Music Performance

"Everything I Wanted" - Billie Eilish

With its deep pulsing bass, breathy vocals, precise imaging, and big soundstage, this selection will tell you a lot about your headphone's capabilities. The U6t comes through with flying colors.

Billie Eilish - everything i wanted (Official Music Video)

Dealer’s Choice – Reviewers Fav Music Performance

“Sleeping on My Dreams” – Jacob Collier on Jacobean Chill

How well does the U6t image? This cut will tell you. It's full of multiple vocals, layered background instrumentation, and lots of complex harmonies. It is a box of sonic chocolates waiting to be opened, which the U6t does beautifully.

High Points

  • Superb build quality and construction. Even the cable gets kudos.
  • 64 Audio's apex modules deliver more outside noise attenuation and frequency response flexibility than any other in-ear design.
  • apex also reduces listener fatigue by reducing ear canal pressurization.

Low Points

  • The U6t may not fit perfectly if you have narrow ear canals.
  • Due to the combination of weight from the U6t's metal enclosure and its size with six balanced armature drivers, they can become loose over time even if initially firmly seated.
  • You get the same driver configuration and technology in a custom-molded in-ear; the A6t.

64 Audio’s U6t is not for you, if...

You are finicky about comfort, especially for long-term use, a custom in-ear monitor will always be a better option than a universal fit.

I suggest the custom version, the A6t, since it delivers a superior fit with a similar sonic character and technology.

64 Audio’s U6t is for you, if...

You're the kind of listener who tries, buys, and then sells as they move up the sonic ladder. Your ultimate in-ear could be the $2999 18-driver 64 Audio U18s. Universal fit in-ears are quite resellable, while custom in-ears are much less so (and at a deeper discount from new) since they must be re-shelled to fit a new owner before they can enjoy them.


Driver Type/Count - Six precision balanced armature drivers

Driver Configuration - 1 tia high, 1 hi-mid, 2 mid, 2 low

Frequency Response - 10Hz – 20kHz

Sensitivity - 108 dB/mW

Impedance - 10Ω Nominal

Crossover - Integrated 4-way passive crossover

Maximum Isolation - -20dB with m20 apex module

Additional Resources

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