64 Audio Duo: Innovation, Elevation – An In-Ear Monitor Review

Select Comparisons

64 Audio A6t ($1299)

This year, aside from the Duo, 64 Audio also put out the U6t; the A6t in universal form. To my ears, the A6t’s the warmer, more robust IEM of the two; less articulate or glitzy up top, along with a stronger focus on the midrange. You’ll get richer, musclier, chestier-sounding instruments on the A6t. Female vocalists will seem smokier and deeper in tone, for example. Whereas, the Duo has a lighter, brighter sound, which emphasises the openness and clarity of the instrument. It’s tighter and quicker than the A6t, which, conversely, will linger a tad more. But, its solid mids pack a punch too, so it’s a different sort of full to the VxV comparison, which we’ll get into later. Still, overall, they’re clearly different-sounding IEMs from 64.

Technically, the one overarching edge that the Duo has over the U6t is the tactility of its instruments. They seem tangible and impactful, while the A6t can tend to have a bit of fuzziness to it. This’s especially true down low, where this Duo’s DD thwacks a lot more convincingly than the A6t’s balance-armatured woofers. Instruments feel further detached from their background on the Duo, while the warmth the A6t naturally has can bind them a little bit. Up top, the Duo extends more as well. Instruments sound freer and airier. Its semi-open design surely plays a part there too. So, for me, the A6t’s more viable over the Duo if you’re specifically after its tube-y, fuzzy sound. But, for the cleaner-cut, open IEM, this Duo’ll take it.

FiR Audio VxV ($999)

The FiR Audio VxV is likely the Duo’s most direct competitor, so it’s fitting that they’re two sides of a similar coin. FiR’s IEM is the fuller, more-relaxed-sounding IEM, while the Duo has more contrast to it. This is because of the former’s fuller low-mids, which makes instruments bolder and – by comparison – less articulate. Whereas, the Duo has slightly tighter, airier instruments, and it has a more elevated low-end as well. So, you get a quicker, more impactful in-ear with the Duo, while the VxV has the edge on genres like jazz or R&B, which take full advantage of its bodied, smooth-sailing, relaxed tonality.

Spatially, the Duo has the cleaner, tidier image for me. Its tighter notes help space them out, and they sound cleaner cut too. The VxV’s have a tad more warmth attached, but they’re in a similar league as far as resolution is concerned. I’d give width to the Duo. Sounds panned hard-left and hard-right feel further apart. But, I’d hand height to the VxV. Instruments have a hair more scale to them on the IEM. And, in terms of end-to-end extension, a slight edge goes to the Duo. Its sub-bass digs further, and its treble cuts with more air too. Still, technical discrepancies aside, it does come down to tonality for me. Those after a fuller, less engaged in-ear have the VxV, while this Duo’ll cater to those after contrast, slam and air.

MMR Gáe Bolg ($1199)

Metal Magic Research’s Gae Bolg is a more intimate, more forward-sounding in-ear than the Duo. While the Duo is more concerned with quick, precise articulation and tidy, roomy imaging, the Gae Bolg is all about bringing instruments closer to you and letting them intermingle. Naturally, the Duo has stronger separation and cleaner layering, while the Gae Bolg takes greater pleasure in immersing the listener through a more with-the-band experience. It isn’t necessarily warmer or more relaxed than the Duo, because of its articulate 6kHz peak. Though, its instruments are a bit less vibrant or brass-y, due to its noticeable 4kHz dip. It also has a fuller, more robust upper-bass, which contributes to its relative forwardness.

When it comes to technique and resolution, I find these two do excel in different respects. The Duo is stronger at, again, separating and picking out little details. It’s quicker and sharper, so you’ll hear lots more clarity here. Whereas, I feel this Gae Bolg is stronger at revealing the lower half of the spectrum. Its elevated and texture-filled low-mids lend a tad more transparency to sounds like male vocals or trombones, while the Duo tends to be more frugal there; again, granting just the amount of body for linearity and naturalness’s sake. Speaking of linearity, this’s somewhere the Duo has the edge to my ears. Its tonality is not as coloured (or shaped) as the Gae Bolg’s is. It’ll work with a wider range of tracks and pairings because of it. But, again, all in all, they’re different, fairly-complementary IEMs that make great options in their price tier.


With the Duo, 64 Audio have made one of their most accessible, yet innovative monitors yet. It mixes a clean, easygoing tonality with a hodgepodge of technologies inside-and-out, yet that cohesion it’s got is darn-near seamless. Considering the sheer breadth of invention in the Duo – from the semi-open apex Core design, to its hybrid driver array – it’s actually impressive how effortless and baked-in it all sounds. Its timbre, though not the most evocative or colourful, is one of the most balanced, easygoing and genre-transcendent 64’s put out yet. And, all that tech I’ve mentioned above just elevates it with the openness, precision and impact it needs to come alive. All in all, 64 Audio’s Duo is a testament to just how far innovation can push a monitor’s ability, it’s an admirable show of consideration from 64 by not limiting their best efforts to just their pricey flagships, and it currently is one of the safest – in a great way – options I’ve heard in the price tier yet.





Church-boy by day and audio-obsessee by night, Daniel Lesmana’s world revolves around the rhythms and melodies we lovingly call: Music. When he’s not behind a console mixing live for a congregation of thousands, engineering records in a studio environment, or making noise behind a drum set, you’ll find him on his laptop analysing audio gear with fervor and glee. Now a specialist in custom IEMs, cables and full-sized headphones, he’s looking to bring his unique sensibilities - as both an enthusiast and a professional - into the reviewer’s space; a place where no man has gone before.


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