64 Audio U6t

64 Audio U6t Review

We review the 64 Audio U6t, which is a universal multi-BA driver in-ear monitor featuring the company’s apex filter system, LID, and tia technology. It is priced at $1299.

Disclaimer: This sample unit was sent to me in exchange for our honest opinion. Headfonics is an independent website with no affiliate links or services. I thank the team at 64 Audio for giving us this opportunity.

To read more about 64 Audio products we reviewed on Headfonics click here.

Note, this 2-page review follows our current scoring guidelines which you can read up on here.

64 Audio U6t
64 Audio U6t Review
I hesitate to say it when the 64 Audio U6t costs a bit over $1k but this is a great everyday carry and plays very well with just about any vocal-centric genre you throw at it. The fact it can be easily driven by most DAPs makes it all the more appealing. Very little to fault here.
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64 Audio continues the reimagination of its Audiophile series of in-ear monitors with the recent launch of its new and more affordable universal product to date, the U6t.

Now, I actually reviewed the original A6 back when it was originally launched in late 2016/early 2017. That is still the mainstay of the company’s lineup to this day under the A6t moniker

This was a custom IEM I described as being listener-friendly with a nice sub-bass lift and good mids with the right cable. A definite break from the older V6 ‘daddy’ back when 64 Audio was known as 1964Ears.

I believe the A6 was also the first to use the apex filter system, a technology that is in just about every monitor 64 Audio has since produced. The U6t, ideally, should be the universal equivalent of the A6t, but with tips and an upgraded cable do we have a different sound signature or more of the same in a more accessible format?

64 Audio U6t
Copyright 64 Audio 2021

Tech Highlights

The U6t is an all BA 6 driver configuration with 2 for the lows, 2 for the mids, 1 mid-high, and a tubeless tia high driver for the highs. This is neatly threaded together using an integrated 4-way passive crossover with a fairly easy-to-drive impedance rating of 10Ω and 108dB SPL.

That is quite different from the original A6 which was rated at 22Ω and 115dB SPL but consistent with the current A6t version they are selling now so there is a possibility that some drivers have changed or been tweaked since 2017.


Tia stands for tubeless in-ear audio and is a key unique selling point for both the A6t, U6t, and their current universal flagship the Fourté.

The U6t, much like its universal siblings, uses the company’s signature tia driver technology first seen in late 2016/2017 though it was not in the original A6 at that time. That may also explain some of the impedance and SPL differences between the older A6 and U6t since sealed BA drivers are often easier to drive than open or vented versions.

At the heart of tia is an open-balanced BA design and is pitched as being far more open in sound than a sealed and tubed BA driver which quite a lot of competing monitors still use. Of course, tubeless drivers are now more prevalent in the market but each has its own unique implementation.

With the diaphragm free of obstruction, the contention is that a lot of the vibrations and resonances you get with closed or tubed designs will be gone.

No more tubes and no more dampers leave more room for the chamber design and a switch to a single wide-bore nozzle. Wide bores produce a more natural sound to my ears than individual channels delivered in tubes right up to the tip.

64 Audio U6t


The U6t also uses 64 Audio’s apex technology with the inclusion of 3 modules: the -10 dB mX module, the -15 dB m15 module, and the -20 dB m20 module. Aside from the m26 solid plug which is only for high-end earplugs, that is the full complement of available filters.

apex is short for Air Pressure Exchange. Essentially the end goal is to reduce the level of pneumatic pressure being delivered alongside sound pressure when inserting and using an IEM or in this case a CIEM.

By reducing this type of pressure, the eardrum gets less of a workover. Thus, the potential of long-term hearing damage is reduced allowing you to safely play music at a louder level than you normally can.

apex works its magic through modules such as the m20, m15, and mX, which are designed to fit snugly into the actual shell of the U6t.

Each module has an opening at the top combined with multi-cell studio-grade TPE material inside that varies in size and composition to produce different audible and sound pressure effects.


The full name for this feature is Linear Impedance Design. Those of you familiar with Custom Art’s FIBAE technology will get a fairly quick understanding of the bigger aim of LID from 64 Audio.

Basically, LID ensures that whatever the impedance level is on any given output you plug the U6t into it should not have a low-Z skew and should play true to its correct tuning.

That means for those holding a 1st gen HiBy R6 or a Shanling M2s with their output impedance ranging from 4Ω to 10Ω there will not be an impedance mismatch and the U6t should sound accurate or ‘true’.

64 Audio U6t


The U6t design retains that signature form factor of the 64 Audio universal series but the final design is a little bit of a mix of everything that has gone before though with a new and even darker paint job. You can call this one a classic audiophile black for want of a better phrase.

That means the U6t has that same matte aluminum shell finish of the U18s but this time in a very dark grey or gunmetal hue rather than black. You also get a similarly glossy front plate as the Nio but with an all-black polish rather than the brighter Abalone.

To the corner, you have the usual apex socket with some very complementary color matching for the mX and the m15 modules. The silver m20 will create more contrast but not in a garish manner.

Just to note, these sample filters do not have the new “64” branding that was on the U18s versions looking more like the older subtler insignia of the Nio. U6t retail version filters might have a newer finish.

Because there are fewer drivers in the U6t compared to the 18-driver U18s the aluminum shell is a little shallower and more in line with the more compact Nio dimensions. Save for the new color scheme and finishing, the dimensions of the Nio and U6t are virtually identical.

64 Audio U6t

Stock Cable


So, we have a new ‘exclusive’ Premium cable to replace the normal standard premium cable and on paper, (and in performance), it is a substantial upgrade. This was the one key area I felt the original A6 needed a big lift in and glad to see some years later we have a good quality stock cable attached to the U6t.

The ‘exclusive’ version is changed from the previous 28AWG ultra-low resistance silver-plated copper (SPC) wire to a new, and larger 26AWG silver-plated OCC copper wire though still a 4-wire geometry as with the original.

As you can expect with a larger gauge the cable will offer a better resistance performance and indeed on paper, it is rated at 0.23Ω compared to the standard Premium cable’s 0.28Ω specification. 

Finishing & Handling

Aesthetically, the next exclusive Premium cable is a bigger build but with a softer shinier black braided jacket to house that larger wire. despite the enhanced girth I actually find this cable more comfortable for handling compared to the original’s harder finish. 

The finishing has changed a bit also. Gone are the right-angle beefy connectors and in comes a svelte straight 3.5mm TRS jack. A new elongated and branded black aluminum splitter and cinch replace the older rubbery disc/cinch also.

Lastly, no retentive memory wire which is replaced by the newer softer springy type which I much prefer. That also helps deaden the cable a bit more for microphonics compared to the original

The U6t exclusive cable also does not tangle as much as the thinner Premium cable. Not that the original was memory retentive, if anything both display the same properties in that regard. Rather when rolling and unrolling the new exclusive version just flops out whereas the original got in a heap of tangles and knots. 

64 Audio U6t

Comfort & Isolation

The comfort levels of the U6t are much the same as the U18s and the Nio which I find favorable despite the weighted aluminum design which is heavier than acrylic alternatives. 

The U6t soft curves and relatively lightweight form factor barely touch the ear or press down uncomfortably. The longish stems might also be helping keep the cable up and away from the sides of your ear where sometimes pressure from the cable can develop.

Just one thing to note is that the U6t sits a bit more flush to the ear much like the Nio due to the smaller form factor. Bigger builds such as the U18s sit out a little further though it’s not a concern when it comes to comfort or passive isolation levels as they are more determined by the type of tip and filter used. 


The traditional influencer for passive isolation are the supplied tips which is the same lineup as the U18s in that cool spidery tip holder tray that also fits neatly into the carry case lid.

You get 3 types of tips, a foam variant called TrueFidelity in small, medium, and large as well as a set of single-bore silicone tips in the same sizes. The 3rd is a set of SpinFit CP145s which I found to isolate the best out of the three supplied ear tips sets as well as providing the highest level of comfort.

The foam tips felt a bit more secure in my ear compared to the softer more pliable silicone tips but neither the silicone nor the foam tips did quite as well for noise attenuation.

64 Audio U18s

apex Modules

Isolation is so-so for the U6t, about the same as the U18s and slightly better than the vented Nio. You can tweak that passive level via the tips which you can read more about below but you can also influence it via the apex filters which both isolate and fine-tune the performance at the same time.

Each supplied filter with the U6t has a varying level of dB noise attenuation that you can pick up on right away. The mX filter isolates the least at -15 dB with the m20 the max at -20 dB. The m15, which is fitted on the U18s out of the box, is rated at -15 dB.

If you want the best isolation then grab the m20 filters but in doing so the sound signature will bring up the bass levels more than the other two modules. The m15 takes it down a notch but with less isolation and the mX isolates the least and as you would expect, offers the least amount of bass quantity of the 3 filters.

64 Audio U6t

Packaging & Accessories

Once again, the U6t packaging borrows a little from what came before, with the narrower Nio packaging and the lift-lid style of the U18s retail box. I see it as more of a trimmed-down U18s box personally but with the internal display and arrangement of the Nio once you open it up.

The outside is the company’s signature black-and-white graphical layout with the monitors front and center. Inside you have the customary introduction from Vitaliy under the lid with the case, monitors, cable, and new carry case on full display inside a contoured foam base. 

Aside from the mentioned tips and tray holder, the accessories also include a collar clip for the cable and a small cleaning brush tool.

64 Audio U6t

Carry Case

I believe this is the same ‘Premium Leather’ carry case as one included with the U18s but with a slightly different finish. This is a rounded high-quality simulation leather and black stitching design as opposed to the yellow stitching on the U18s version. It is soft but strong on the outside with the distinctive new 64 Audio logo embossed on the front.

The inside is fairly spacious with plenty of room to fit in a cable or two, the monitors, and even the spider-wed tips tray on top. The sides, top, and inside of the lid are padded with a cloth material so your monitors will not suffer from any undue knocks from day-to-day carrying. 

It is marginally too big to be easily pocketable which smaller plastic containers or soft pouches could offer but it will have no issues being thrown into small bags on the go.

Click on page 2 for my sound impressions and recommended pairings

Click on page 3 below for my selected comparisons.

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