I wanted to share some more thoughts on the Duo because I brought one back with me from CanJam. As far as I can tell, 64A basically has three flavors of sound: their “reference” audiophile tuning (which consists of the U12t, U6t, U18s, and to some extent the Nio), their audiophile tuning (the Tia Trio and Tia Fourte), and their mainstream tuning (the U18t). The Duo straddles the line of the previously somewhat lone Nio while adding on some extra flair up top, presenting a comparatively new flavor, if not one that will be readily familiar to fans of the brand. But before I get ahead of myself, I should share some thoughts on the Duo’s physical design.
In a nutshell, I LOVE the Duo’s design. The grill doesn’t look cheap at all to me and it’s super pleasing aesthetically. Something different about the shell of the Duo is that it has been anodized what appears to be a slight shade of midnight blue (or maybe I’m just colorblind). Either way, the Duo looks fantastic. And it’s just as ergonomic too. While I didn’t get in a size comparison in the photos above, it’s the shortest of 64 Audio’s IEMs in terms of shell depth. I spent about 5+ hours jamming out to them today and not once did I feel the need to remove them outside of instinctively yanking them out when someone spoke to me. I say “instinctively” because you don’t really need to remove them; you can actually hear people talking if you just pause your music. Anyways, that’s more than enough talk about build coming from me - let’s talk about the actual sound.
As stated above, the Duo shares some similarities to the 64A Nio, and that’s primarily in one aspect: the fat bass shelf. That said, the Nio sports more of a sub-bass focus and for a sense of digging into the deepest frequencies and generating them with a sense of thickness and weight, the Nio comes out ahead in A/B. In this respect, at least intangibly, I do find the Duo’s bass to be more reminiscent of the DD used in the Tia Trio. The Duo’s bass is more nimble than the Nio’s bass response thanks to less decay, and it sounds fairly rich whilst avoiding the wooly thickness of the Nio. I also have no qualms on the fronts of bass texture. As far as I’m concerned, the quicker bass response of the Duo’s DD was the right tradeoff, as the Nio’s subwoofer generally sounds more sloppy when it comes the mid-bass. The Duo generally has pretty good bass - not the best I’ve heard for this price point, that honor goes to the Sennheiser IE900 - but certainly enough to merit comment. And remember, the Duo’s DD is tokening the entire midrange too.
Speaking of the midrange of the Duo, it’s pretty alright. The overall amplitude of the pinna compensation has not changed too much - it still leans toward the more relaxed side - but it does not peak until 3kHz unlike most of 64A’s other IEMs which tend to peak a bit earlier at around 2kHz. This lends the Duo to a slightly more upfront center image, but 64A has recessed the presence regions from 3-4kHz to avoid sibilance per usual. Intangibly, vocals consequently hang slightly higher on the stage while staying upfront for me. I don’t think this midrange presentation is quite perfect, but it is an interesting tuning decision that, again, demonstrates to me that 64A really knows how to tune. Expectedly, the timbre of this midrange is quite pleasant with none of the timbral inconsistency that characterizes most hybrids between bass and midrange. This part was really was nice to hear.
The treble on my unit seems to be somewhat different from the unit I heard on the show floor. I remember the show floor unit sporting more of a lower-treble emphasis which beget a more V-shaped sound signature. However, I will assume for now that the unit I have on-hand represents the ideal sound, as the Duo’s product page markets it as having a more laidback sound signature. This is indeed a boon with respect to coherency, as I felt that the tia treble on the show floor unit was a tad too distinct from its DD counterpart. But make no mistake: This can still be a bright IEM depending on the ear tips you’re using, your hearing, and the volume you’re listening at. In fact, I feel that the tia peaks on this Duo are higher in amplitude than on my U12t - they’re definitely higher than the Nio - and almost sharp on certain tracks with wide-bore tips. This was consistent among all three units I heard; hell, I hear what sounds like a 16kHz sheen when Taeyeon enters on “I Found You” that I didn’t know was there before. Further along the lines of frequency response, I’d say the Duo’s treble is about 40% lower-treble, 20% mid-treble, and 40% upper-treble. I don’t know if it’s quite right to market this as a relaxed IEM but, to be fair, swapping to the foam tips will definitely mitigate any unwanted shimmer as I found on Day 1 of CanJam.
Imaging on the Duo is interesting. It’s good, but it’s not mind-blowing within the context of the more open nature of the IEM. The Duo’s biggest weakness on this front would be localization of instruments. They’re somewhat undefined and clearly not as sharp as the Symphonium Helios. But to reiterate, the Duo definitely sports above-average imaging, and I think the best way to describe it would be simply “natural”. Sounds mesh into the backdrop pleasingly and there’s a good sense of ambiance to the Duo’s staging. However, there’ll be no cop-outs on the front of detail, I’m afraid. The tia treble holds its own in terms of detail, but I simply don’t find the Duo particularly detailed in the midrange which is why I called the midrange “pretty alight” earlier. It sounds slightly smoothed over in A/B with the 64A U6t which I don’t even consider a strong performer for detail, and the Sennheiser IE900 which has a disgusting upper-midrange recession. This is ostensibly a limitation of using a single dynamic driver to cover both the bass and the midrange frequencies, even a high-quality one at that.
The best part of the Duo’s intangibles would be its dynamics. They’re surprisingly good; I wouldn’t have bought one for myself if I thought they weren’t. Now, I do not think the Duo has great micro-dynamic distinction - a sense of individual instruments and vocalists popping with subtle fluctuations in volume - but it stands that the vast majority of IEMs lack this quality anyways. In fact, the only IEM I have heard with good micro-contrast at this price point would be the Symphonium Helios. That said, macro-contrast on the Duo has the good sense of weight and authority that characterizes the likes of the 64A Nio. I found myself jacking up the volume and going back to swings like Sawano Hiroyuki’s “Tranquility” at 0:50 repeatedly just to catch more of this quality while testing the Duo at CanJam. I do not know how 64A does it, and maybe you can consider it the “oh, he’s just a 64A shill” effect, but there is definitely something about the likes of the U12t, Nio, and the Duo that catches my attention and gets my head bobbing.
As for some concluding thoughts, the Duo is definitely a good IEM and I like it! But I also cannot ignore the price in good faith, and I don’t want to make the mistake of hyping something that won’t get near-universal praise. It’s crucial to recognize that the Duo sports a more niche design; it heavily emphasizes comfort and it doesn’t befit outside use like traditional IEMs unless you’re indexing more strongly for situational awareness. For me, that’s what I wanted as a compliment to my Symphonium Helios. I’d imagine this would work great for walking outside too and, as the reps at the 64A booth mentioned to me, streaming and gaming. But it still pays to recognize that not everyone else will have these use cases; solely on the basis of sound quality, I find the Duo to be solid for the price but not necessarily outside the scope of the lofty expectations I hold for 64A.
All that said, there is a lot of unique technology and innovation packed into the Duo. Friends better versed in the construction of IEMs than myself have commented on the complexity of 64A’s crossover design, and I enjoy the emphasis placed upon the user-experience with technologies like Apex Core - after all, the best sounding IEM doesn’t mean much if one can’t wear it comfortably.