64Audio Duo Review – Fun, Forgiving, Fabulous

Comparisons –

Fir Audio VxV ($999): A five driver hybrid with a more balanced bass, in particular, but a slew of similar technologies including a tubeless design. The VxV has a similar bass voicing but with less emphasis throughout. The Duo sounds more musclular and bold, the VxV cleaner but still bold and weighted due to a modest sub-bass focus. The Duo is thicker with less separation. It has a more assertive attack and slam while the VxV is more controlled, separated and defined. The VxV comes across as more articulate and resolving while the Duo is more bombastic.

The midrange stands out more on the VxV by comparison to its less present bass. The Duo has a slightly more even tuning, it is warmer due to its bigger bass, both are similarly dense in the upper-midrange. The VxV has a lighter note weight and a more revealing character as a result. The Duo is less separated but fuller and more powerful. Though more laid-back, it is much more forgiving and no less extended or articulate. The VxV has a slight resolution advantage aided by its cleaner tonality. The Duo is for those that prefer a more organic and full-bodied sound as some find the VxV to be on the thinner side.

The VxV has a similar treble tuning with dual lower and middle-treble peaks, albeit, to a lesser extent in the lower-treble. As it has less bass, this is in good taste, providing a more even-handed listening experience. The VxV shifts the peak slightly higher to 6k, combined with its tubeless drivers, it provides a slightly more defined leading edge, delivering percussion with more bite and crispness. The Duo has a bit more body and texture in return, both are equally well-detailed and standouts at this price. The VxV has a hair more air and headroom but both are also excellent here. The VxV actually has a wider stage while the Duo is deeper. The VxV does have slightly sharper imaging to my ears.

Rai Penta ($1099): The Rai Penta is a more balanced hybrid competitors but makes for good comparison if you are attracted more to the warm, smooth midrange of the Duo rather than its bass. The Penta delivers just this alongside a more balanced, even-handed bass. Its low-end is flatter and a bit more rolled-off at the very bottom with greater mid-bass focus. The Duo is quite a bit bassier and much more aggressively textured. It has greater deep-bass focus, lending it a more weighted and powerful voicing. Meanwhile, the Rai Penta is more separated and natural. The Duo sounds equally well-controlled to me, just a hair less articulate but much more dynamic. The Penta is better suited for those valuing greater linearity.

The midrange character is slightly different on the Rai Penta, it is if anything slightly mid-focused, involving greater centre-midrange focus due to its lesser bass. This gives it larger note and greater structure in tandem with a smooth, dark articulation. The Duo sounds higher contrast and more engaging but equally well structed. This is because it has more bass to fill in body and warmth. It has more density paired with a more defined articulation. The Duo sounds more detailed here and resolving of fine detail. The Rai Penta has a smoother voicing altogether with greater focus on midrange elements but is considerably less engaging in so doing.

The Rai Penta has less lower-treble but more middle-treble focus giving it a more overtly airy and atmospheric presentation. Its lower-treble is much smoother meaning it lacks the same bite and crispness of the Duo. The Duo, in turn, sounds quite a bit more detailed here while the Rai Penta is a bit more open but substantially less focused. The Duo also extends better delivering more sparkle and headroom, the Rai Penta sounds less complex overall. The Duo has a larger stage and sharper imaging to boot. The Rai Penta separates better through the mids and bass.

Campfire Audio Dorado 2020 ($1099): While many are quick to compare the Duo with CFA’s BA monitors, I do think the bassier hybrid Dorado targets a more similar niche. The Dorado 2020 has a similarly sized bass shelf but it is wider extending more linearly into both the sub and mid-bass. In turn, it comes across as slightly bassier and with a thicker note structure. The Duo is a bit cleaner and more separated. It doesn’t quite have the same assertive attack and sub-bass power as the Dorado, but sounds more defined and is slightly quicker decaying, enabling more defined notes overall. Meanwhile, the Dorado maximises dynamics having stronger impact properties at the cost of responsiveness.

The midrange is cleaner and more delicate on the Duo, being thicker, more robust and boxier on the Dorado. The Dorado has slightly less vocal presence with a better balance between instruments and vocals. It picks up a bit more warmth from the bass and has greater centre-midrange presence which gives it a grander note size. Meanwhile, the Duo is more progressive in its tuning, sounding more separated, balanced and natural, in turn. The Dorado does have a hint more lower-treble and less of an upper-mid dip, but not enough to fully counteract its greater body and warmth. In turn, it appeals most to those wanting such a full and hearty midrange voicing.

As aforementioned, the Dorado 2020 does have a slightly more prominent lower-treble while the Duo is slightly airier with greater middle-treble shimmer. The Dorado 2020 has a darker background and higher contrast in turn. Parallels can be seen between tia and TAEC in terms of note presentation, both delivering plenty of sparkle and a very clean response overall. I do think the Duo sounds a bit more nuanced. It has slightly better separation and texture, the Dorado 2020 is crispier with more bite but has less fine detail through the body of the note. The Duo provides a slightly larger stage altogether and better separation. The Dorado 2020 appears to offer slightly sharper localisation in return.

Lime Ears Aether R (1100 UER): The Aether R is a warm-leaning 6xBA IEM with a switchable bass boost that puts it about on par with the Duo for quantity. It also has similar approach to midrange tuning with a focus on density and smoothness. Its 3D printed low-pass filter gives it impressive depth for a BA monitor but it doesn’t provide the same authority and pressure in the sub-bass as focus lies in the mid-bass. The Aether R delivers rounder, warmer note in turn with less weight and power. The Duo is a substantially more weighted, dynamic sounding earphone due to its lower peak and DD design. The Aether R has fairly typical BA attack and decay, being very fast which gives it a separation advantage but also saps the same natural texture and timbre provided by the Duo.

Indeed, the midrange sounds fairly similar on both when the bass boost is activated on the Aether R. The Duo sounds a touch cleaner tonally while the Aether R is a more revealing up top with a dew dB more pinna gain. In turn, the Aether R does come across as a bit more balanced with greater clarity. Its density and slightly greater warmth means it isn’t intense either. The Duo is more structured and coherent yet. Though more laid-back, it commands richer body and is more forgiving. The Aether R returns with greater resolution, bringing fine details more to the fore. The Duo does smooth over fine details more than competitors in favour of its smooth, forgiving and organic voicing.

The Duo definitely has an edge when it comes to treble delivery, quite literally. The tia driver delivers a more defined lead-edge and simply a more detailed image. Both have a similar level of lower-treble, the Duo has greater middle-treble air and shimmer while the Aether R has higher-contrast and slightly more upper-treble presence. Overall, the Duo is more resolving and textured. The Aether R has a nice tonality but falls behind on sheer resolution. In terms of soundstage, the Aether R is also similarly proportioned, the Duo is slightly more expansive while the Aether R has a bit more separation.

64 Audio U6t ($1399): 64 Audio’s previously most affordable universal IEM, the U6t assumes a 6x BA setup and features exchangeable apex modules to taylor the sound. The following comments will be using the stock M15 modules. The U6t provides a more balanced sound with less bass bias and a more focused treble detail presentation. Despite its all BA setup, it provides a good amount of authority and power in the sub-bass, albeit, lacks the same pressure and rumble of the DD-driven Duo. The Duo has a more prominent bass, but it is also warmer in its voicing, the U6t having a sharper cut through its mid and upper bass that makes it sound more weighted and contrasted but also tonally cleaner. The U6t is faster while the Duo offers better dynamics and greater impact.

The midrange is more prominent on the U6t and peaks slightly sooner, giving it slightly better balance between male and female vocals. Both are on the smooth and coherent side, the U6t comes across as more balanced and slightly more revealing due to its more present lower-treble and upper-midrange. The Duo is one step smoother and warmer, its bass is bigger and its upper-midrange is sizably less present. In turn, the Duo is more coherent but also less open. The U6t has better resolution and note definition here, aided twofold by its more revealing tuning.

The U6t also has a more prominent lower-treble. It has more bite and crunch which heightens the impression of details. The Duo is airier but more diffuse in this regard. Both are extended and sparkly, the U6t comes across as more detailed due to its greater lower-treble presence, it has a darker background but also less air. This means that neither are especially airy and well-separated but for different reasons. The U6t does provide a bit more width to my ears, and more even soundstage proportions with sharper imaging. Meanwhile, the Duo provides greater depth and it has slightly better layering.

Verdict –

The Duo carves an intriguing niche as a bass-forward and open-back IEM; two qualities not usually associated but were intentionally targeted by 64 Audio purely for this reason. The result is an enjoyable experience that is difficult to replicate. The Duo carries itself comfortably and with zero wearing pressure on top. Similarly, the listener can enjoy greater situational awareness than regular IEM designs similar to an open-back headphone. The sound is where things get interesting. At its foundation, the Duo will be broadly appealing due to its combination of powerful bass and natural vocals with enough treble clarity to cut through the mix. While it won’t suit those wanting the most detailed, revealing midrange nor great overall balance, the Duo is very forgiving and genre versatile, with very innocuous colouration altogether.

Due to LID, you can also enjoy this consistently from a wide range of sources whilst still scaling well with better amplification. Interestingly, the Duo doesn’t have an especially wide stage nor the most focused, crisp treble response. I think it is important to reiterate this given these qualities are almost expected from 64 Audio IEMs. This makes the Duo a very unique experience not only for the brand but in general. While the U6t will be the more versatile buy, the Duo definitely makes a lot of sense for a more specific demographic that has been less catered to in the IEM market. If you enjoy a coherent, bass-forward sound, are averse to IEM wearing pressure but don’t want to miss out on top-level treble extension, the Duo is without equal.

The U6t can be purchased from 64 Audio for $1199 USD at the time of review. I am not affiliated with 64 Audio and receive no earnings from purchases through this link.

Track List –

Billie Eilish – dont smile at me

Bob Seger – Night Moves

Courtney Barnett – Rae Street

Cream – Wheels of Fire

Dire Straits – Communique

Dirty Loops – Next To You

Eagles – Hotel California

Elton John – Honky Chateau

Fleetwood Mac – Rumours

H.E.R – I Used To Know Her

Jasen – BYE

John Mayer – Continuum

Kanye West – Ye

Missy Higgins – The Sound of White

Radiohead – OK Computer

TALA – ain’t leavin` without you

The Beatles – Abbey Road

The weeknd – After Hours

Vampire Weekend – Father of the Bride