64 Audio A18s: The Quartermaster – A Custom In-Ear Monitor Review


With either module, this A18s delivers a smooth, laidback neutrality with elevations in bigness, meatiness and muscle. It reads fairly natural – free of most dominant frequencies – apart from broad rises across its rich, gutsy upper-bass and its meaty centre-mids. The colourations add boldness and body to instruments, as well as a larger, warmer note. Combined with a more relaxed 4-5kHz range, the A18s isn’t as bite-y or crisp as its Tzar counterpart. But, what it does lend in return is weight and control; ideal for those who may have found the A18t bright; edgy. I could see it being particularly favoured on stage, because of how capable it is of outputting superb air and detail over long sessions without too much sizzle – a smoother, more refined grade of resolution – followed by that midrange lift for some lovely oomph across the board too.

Spatially, despite its smoother, reined-in highs, this A18s boasts a similar capacity for stage expansion, imaging precision and stereo separation as the Tzar counterpart. Depth has gone up a notch, even, due to the s’s more level-headed, more relaxed transients. The image it throws out is palpably open, well-defined and effortlessly holographic, topped off with a pristine background and reference-grade resolution. This clean canvas allows notes to still cut through with great punch, despite this A18s’s more organic tonality. And, they’ll always come off textured and defined too, so that midrange oomph won’t turn into congestion. Separation is stellar too, though not as magnified and clinical as the A18t, simply by virtue of treble content. But, those after a softer, more linear tonality with their technical chops will find much to love in the A18s.


Whether on the m15 or the m20, the A18s has a weighty, full-bodied, warm-sounding low-end. This profile’s decided by a mid-bass bias, leaving the sub-bass more modest by comparison; slightly tapering off as it reaches skull-rattling (or bone-conducting) territory. So, quantity-wise, it isn’t a low-end I’d immediately recommend to a basshead. Again, no matter the module, the A18s isn’t made to rattle. The N8 or Nio from 64’s stable may be more fitting there. That aside, however, this bottom-end delivers quality plentifully. Kick drums have roundedness and oomph, bass guitars cut effortlessly, and that is all done while maintaining space too. Thanks to that reserved sub-bass, these instruments are allowed to play without overshadowing the ensemble; resulting in a bass that’s musical and selfless, as long as you don’t mind a touch less verve.

With its slight emphasis on being heard, rather than being felt, this A18s’s bottom-end lends itself nicely to a use-case like tone-shaping or processing. Because there’s very little colouration to these lows rumble-wise, the tonality of instruments like the kick drum or toms should come through transparently. With resolution, coherence and extension there too, it’s a great Litmus test for live shows, on-the-road mixing or an alternative mastering reference, even. Now, where I’d be more cautious with the A18s as a sole reference would be when, again, dealing with sub-bass frequencies. Whether it’s judging lows on an EDM mix or phase between a bass guitar and a kick, it isn’t as sensitive to me. And, again, in listening, despite the bigness, power and warmth of this low-end, it’s not one to necessarily grab you by the teeth with rumble. But, as long as you’re aware of that, the A18s down low should more than suffice most audiophile preferences and professional uses.

Speaking briefly to the effects of apex, the default m20 module will give you a fuller, warmer and more mid-bass-present sound. I can’t hear any appreciable change in the sub-bass, so you’d probably have to go all the way up to the m26 if you wanna push as much rumble as possible out of those low drivers. The m15 module will take a bit of body out of the mid-bass, which puts the in-ear’s focus squarely on the centre-midrange. That is ideal if you want to listen exclusively to male vocals or saxophones. And, it can also introduce a bit more air into the stage if a more open sound is what you want too.


The midrange is where this A18s, to me, puts its grooviest foot forward; forming the foundation of its presentation, and – to some degree – driving it forward too. It’s a full-bodied vocal range with density and weight, but not the wet, resonant, buttery kind you’d find in traditionally warmer monitors. The A18s delivers loads of texture and nuance here, constantly maintaining a sense of tightness, clarity and control within the gruff, chesty and substantial timbre. Snares, for example, will have a slightly more low-tuned sound with equal quantities of crackle and body; both thud and clang. But, they never lose the cut and grit coming from both the skin and the snare wires. Vocals, similarly, will have a deeper, chestier timbre; less sweet and more meaty. But, they’ll articulate and project as clear as ever, allowing for both naturalness and resolve.

Technically, again, texture is a particular strong suit for this A18s, especially along the lower-mids, where the Tzar tended to be a tad shy. You’ll be able to glean more detail and dynamics from male vocals, toms, trombones, baritone saxes and the like. And, more notably, they have greater physicality to them too; not as quick, light or mild. This allows instruments to come off more complete and well-rounded, and will be ideal to those who may’ve found the A18t a tad top-heavy. The high-mids, then, as discussed in Presentation, will take a bit of a step back. This may not be ideal if you prefer your female vocals peppy and light, or your horns brassy and bright. But, on the other hand, engineers who’d require an even, linear, unexaggerated look at the big picture should find this midrange nicely balanced, and brimming with detail and space too.


Up top, the A18s shows an admirable degree of restraint, opting for a sound significantly more level-headed and relaxed than the majority of their tia in-ears. While this tech has been known for both its immense clarity and its slight sizzle, the s shows here that the two aren’t always mutually inclusive. Its high-end has air, clarity and cut in spades, but pairs it with a relaxed, unvarnished response free of any noticeable peaks. Cymbals and hi-hats won’t jump at you like they would on the Tzar. Instead, they’re delivered with a more delicate, smooth, slightly feathered touch. The crashes on Snarky Puppy’s What About Me are a hair behind the guitars and snare, for example. And, they lean more towards a shh.. than a hard tss..

Now, that shift relative to the A18t has its pros and cons. Those who may’ve loved the Tzar’s crisp, surgical precision may find this more organic response a tad damped or shelved down. There’ll certainly be those who’ll miss the sizzle and the cut it brought along with it. But, on the other hand, I think it is a change that makes this iteration of the A18 more studio-appropriate as well. Transients now mesh seamlessly with the lows and mids; an organic component of the note, rather than tizzes that distract from them. Positioning is more even too. As mentioned above, cymbals sit unexaggeratedly with the ensemble, which gives its stage a deeper, more even, more spherical look. So, if you prefer seamless coherence over clinical analysis, the A18s will surely please; extension and air at a TOTL tier, and primed for hours of studio work as well.

General Recommendations

64 Audio’s reprise of their 18-driver flagship offers shifts to forwardness, tone and treble response for a more agreeable, understated and organic hue. Below are three of its stand-out qualities, and why one might consider the A18s over the t:

A peak-free, studio-ready response: This is one of the bigger changes 64 Audio have made with the A18s; levelling off those (potentially) sizzl-y treble peaks for a tonality that’s more linear and – to my ears – tonally transparent. You’re getting less of the in-ear’s colouration and more of the track’s, which is what you want in a reference monitor. That makes the A18s a strong option for engineers, and, at the same time, an alternative to those who may’ve found the Tzar a hair too sparkly.

Neutrality with fullness, and body with definition: The A18s also makes a fine option for vocalists and musicians, because of its mix of clarity and weight. Drummers monitoring their snare hits will find both thud and clang translated clearly on this in-ear, for example, and singers should find this added warmth desirable for longer sets too. At the same time, that body isn’t had at much cost to technical performance, so enthusiasts shall still get their fair share of detail out of this A18s too.

Top-class imaging, texture and resolution: Like the A18t, the A18s is capable of delivering best-in-class detail, dynamics and nuance. Though it isn’t as clinical a separator as its Tzar counterpart, it compensates with a fuller lower-half, along with a more transparent tone. So, despite the calmer sig, technique remains as compelling a selling point as ever for this in-ear.

On the flip side, those changes 64 have brought on may not be appreciated by all. There’ll be those who prefer the Tzar’s analytical sound, as well as some of its brighter edges. Below are three attributes you certainly wouldn’t get on this A18s:

Super-crisp, sparkly transients: The A18s’s relatively withdrawn top-end means its transients – its leading edges – will come off unexaggerated or unexcited. They may even sound soft if your baseline is the A18t, or a headphone like Sennheiser’s HD800, for example. While it never nears muffle or roll-off, it probably won’t satisfy the most eager of trebleheads either.

A lean, clinical midrange: The A18s’s 2kHz lift definitively endows the midrange with gruffness, chestiness and weight, and it could be a denser midrange than – again – fans of the A18t or HD800 are used to. Snare drums have oomph with clang, vocalists may have a heavier tone, etc. So, however ideal it may be for note structure, warmth and naturalness of tone, if raw, clinical, surgical separation is your ultimate criteria, 64’s A18t – or Fourté, even – would make the more ideal choice.

A sub-bass emphasis: Although the A18s has power and texture in spades down low, it won’t necessarily emphasise those visceral, spine-tingling frequencies at the very bottom. Whether you’re listening to 808s or classic, house drops, it simply will not compromise its balance enough to deliver that type of rush. So, if you’re more inclined towards those genres, or you simply crave the most visceral bass possible, the A18s may not be as ideal as, perhaps, 64’s hybrid Nio, N8 or Fourté.





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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