64Audio Duo

The Baby 64Audio

Pros: BASS
Instrument separation
Cable – but it’s only 3.5mm
Almost no sibilance or harshness in highs

Cons: Recessed mids
Recessed highs

Duo Front.jpg


Eeets So Leeetle. I’m kidding, it’s the same size as every other 64Audio IEM. The Duo is the cheapest though at $1,200. It also only has two drivers – and it’s semi-open-back. Wow. It’s also lightweight and won’t cause eardrum pressure thanks to the open…ness. The Duo has a Tia high driver and a Dynamic lower driver. My initial impressions of it weren’t that great but I had just listened to the Mezzo, which is not really in the Duo’s league. So how does it do against other IEMs in its class? Well, I have the Thieaudio Monarch Mk2 (MMk2) and the Empire Ears ESR Mk2 (ESR) on my desk to compare. LET THE BATTLE OF THE TWO’s COMMENCE! (See what I did there?)

Build Quality / Comfort:

The build quality on the Duo is pretty good. but feels a little cheap. The little mesh grill covers are top-notch and feel really sturdy. The shell is comfortable and of good quality, though it feels plasticky (their website doesn’t say what it is – could be plastic or metal.) These look like they won’t scratch easily and they can’t bubble like resin (ESR *Cough*) so they would be great everyday IEMs you wouldn’t have to worry about damaging. I do worry about getting lint and dust inside them with the semi-open ear plates, but it’s probably not a big deal. The case is a nice leather circle (that is easy to open…Aroma…) and the ear tips fit inside it along with some filters and a cleaner. It’s a good presentation, though the foam holds on to the IEMs REALLY hard – careful removing them so you don’t break off a cable pin inside the Duo.

The stock cable on these is actually pretty decent. 4-strand multi-twist with silver plated copper – 26 AWG. Nice. Too bad it’s 3.5mm – but it’s still quite nice compared to some – I’d use it if it was 4.4mm. Instead, I’ll be using my trusty modular Kinnera Leyding for testing because…it’s awesome (you can get one here if you feel like it: https://amzn.to/3l4O2Z1.) Ditto for the ear tips – the ones that come with the Duo are pretty nice and there’s a good selection, but mine was used and they’re covered in…stuff…so I’ll be using my Spinfit W1 tips (also, if you want some of these, they’re here: https://amzn.to/3XXudBt.) I use the small size to get a really good fit (yeah, it sucks you can’t just order one size – I don’t need 3.) The comfort level with the Duo is really good; it’s what I would classify as Schmedium – around the size of the ESR – MUCH smaller and more comfortable than the MMk2.

Duo Accessories.jpg

Sound / Source / Comparisons:

Looking at the squig.link frequency response graph, the MMk2, and the Duo are very different in most every measure. The Monarch has a tiny bit of increased sub-bass at 20 Hz – but then the Duo overtakes it HARD until the mid-range where they meet for a second and then careen off in different directions once more with the Duo having much more muted upper-mids and low-highs. It will be interesting to see how different songs play out between these two. I’m not including the ESR in this comparison because it has VERY different tuning (far less bass.)

MMk2 DUO.png

I will be running the ESR and MMk2 from my Shangling M3 Ultra (M3U) using 4.4mm from Tidal Hi-Fi. I am running the Duo at 27/100, which is still quite a bit lower than the MMk2 (35-40/100), but far less than the Vision Ears VE8. The lower volume will save some battery in the long run on mobile devices, but there are more efficient headphones if that’s your thing.

As usual, I don’t like breaking down headphones solely by frequency range since every song has bass, mids, and highs (and I can’t tell the difference between vocals at 1900 Hz and 2100 Hz.) So, I will start with bass-heavy songs, then move to mids-focused and lastly highs-focused songs, then break down each song by how all the pieces are presented. You can find my Tidal test tracks playlist in my signature if you want to compare them to your headphones. As usual, I am going to start with the bass-heavy song by David Guetta, “I’m Good (Blue.)” The intro kick drums have lots of impact without any bloat. The mid-synths sound great and the Sub-bass has that breath-stopping quantity that I look for from this song. These are really bassy IEMs – something we should expect from the freq chart. The soundstage sounds wide and open (not surprising with the semi-open design.) The mids sound further back than on the MMk2 (Which is one of the most mids-forward IEMs I’ve heard.) The Duo manages to avoid the sub-bass bloat that even the excellent Aroma Thunder exhibits on this song. For my preference though, I like the forward mids of the Monarch on this song better (I am not a basshead.) The MMk2 has more bloat/extra reverb on the intro bass drums – back to back, the Monarch’s bass is worse than the Duo. The mids are definitely better/more forward/clearer. So between these two, Duo wins bass with tighter/more forward/controlled/impactful bass, Monarch wins mids with more forward/musical mids, and highs are more pronounced on the MMk2 (whether or not that’s a win is up to you.) But, since this is the bass test song, Duo wins the bass.

For the Mids-test, I am using Peter Schilling’s “Major Tom” (which has to be turned up because it’s quiet on Tidal.) The intro synths come in nicely on the Duo, though a little muddier than they do on the Monarch (once again, the Monarch is world-class on the mids, so there’s bound to be some weakness here.) Still, the guitars and vocals sound really good and the bass drums don’t overwhelm the rest of the song. The transition at 1:20 sounds good and has no technical issues. The song comes in clean with all of the instruments having clear separation with an excellent soundstage. Just like the previous song, the MMk2 emphasizes the mids more – so vocals sound very forward and guitars sound crisp and clean on the Monarch (especially at 4:08 where we get into the high vocals – the best part of the song, the MMk2 does it better but the Duo is no slouch here.) The monarch’s bass drums feel very recessed on this song – the Duo gives them more body. The same goes for the bass guitar which is more emphasized on the Duo. There is an annoying sound in the right ear on this song that the MMk2 makes more obvious than the Duo – I will probably never use this song as a test song again because of that sound (never heard it on speakers before, but IEMs exacerbate it. MMk2 win here.

Moving on to “High Hopes” by Panic! At The Disco to test for sibilant “S” sounds. These sounds come in over 3k Hz, so with the Duo recessed treble it could decrease the sibilance on this song – and it does. This is one of the least sibilant colorations I’ve heard on this song. There is almost no sibilance throughout the song (a little bit, but it’s only noticeable if you’re looking for it – which I am.) The vocals, soundstage, instrument separation, horns, and drums all come in clearly – this is a really good song for the Duo. Of course, the Monarch has forward mids here and the drums and horns (which reach into the low-mids frequency) actually get lost a little bit in the background compared to the Duo. The Monarch sounds sharper in the highs here compared to the Duo, but it still manages to avoid most of the sibilance – there is more than on the Duo if you’re listening to it, but the Monarch still has some of the best highs you’ll find in this price range. Those of you looking for highlighted highs will want to avoid the Duo – those of you who hate sharper/pronounced highs and love more low-end will love the Duo. Duo win

Well, how does the Duo sound with Michelle McLaughlin’s “Across the Burren?” Really good, the soundstage is massive and recessed highs allow this song to present the piano without any of the harshness that some IEMs/Headphones can display here. If you’re worried that the recessed highs mean that the piano won’t come in nicely, you have nothing to worry about – the piano still comes in nicely, though those of you looking for “Sparkle” may dislike the Duo. There is nothing “recessed” about this song on the Duo – it sounds really good – not Mezzo or Thunder good, but really good nonetheless. The Monarch highlights some of the background noise in this song, which can actually be a little annoying. The notes on the piano are beautifully presented though. There is some sharpness that isn’t present with the Duo, but overall, the MMk2 makes the piano sound more beautiful than the Duo (sparkle anyone?) Tie?

Duo Corvette.jpg


This is a pretty easy conclusion. The Duo are for people who like low-end more than anything else. You can see on the Freq chart that 64Audio put that as their emphasis and it really shows. Great quality/quantity bass is the Duo’s forte, though it has a good soundstage and instrument separation as well. The mids and highs are definitely more recessed, which may be some people’s preference. If you prefer a similar soundstage and mids/highs forward, the MMk2 remains one of the best in its class. The ESR is also a good option in this price range if you want a great-sounding IEM with less bass than either the MMk2 or Duo with more balanced mids and highs.

You can buy them from Audio46 using my affiliate link if you want: https://audio46.com/?ref=wolfhawkaudioreview.com

Headphone Scoring:
Build Quality0.8​
Ear Pads / Tips1​

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