The comparison was done using Duo with a stock 3.5mm cable, SpinFit CP145 stock eartips, and LPGT as my source, volume matched in every comparison.
Duo vs 64 Audio Nio – Had to bump Nio to M20 module to come closer to the weight and the impact of Duo’s bass. That gives a good match in sub-bass rumble and a similar mid-bass impact. Duo has a fuller body lower mids, while Nio’s lower mids are leaner, and as a result Duo’s mids sound a bit thicker while Nio’s mids (vocals) have a little better definition. This difference in mids was more noticeable with vocals rather than instruments. When it comes to treble, Duo is brighter and has more air with better extension in comparison to Nio. Furthermore, the soundstage is more open in Duo, especially since I’m using M20 (20dB) apex with Nio which has more isolation.
Is Nio worth extra $500? IMHO, yes, considering you have replaceable apex module and prettier blue abalone faceplate. But if you don’t care about it and prefer more open sound and authorative bass impact, then Duo would be a good choice. But also keep in mind, Nio will have better isolation while Duo by design is not.
Duo vs 64 Audio Trio – The sound signature is the first thing that stands out when you start comparing these iems, both do have recessed mids, but Trio is V-shaped with a deeper cut in mids while Duo is closer to U-shaped. Both have a very similar bass down to a deeper sub-bass extension and punchy mid-bass. Duo’s lower mids have more body which gives its mids/vocals more organic tonality, while Trio’s lower mids are very lean which translates into a thinner and brighter mids/vocals. Treble is another extreme with Duo being smoother and more natural while Trio treble being a lot more brighter and piercing. Soundstage expansion is actually not too far off, but Duo does give you a more open sound perception.
Duo vs 64 Audio U12t – I was using U12t w/M15, but its soundstage is still a little narrower in comparison to Duo. The overall sound sig of U12t is more balanced while Duo has a U-shaped signature. Duo has more elevated bass, definitely more weight with deeper rumble and stronger mid-bass, making U12t sound leaner and even more neutral in a relative comparison. Mids of U12t are leaner as well because of less body in lower mids, while Duo has thicker and warmer mids with fuller and richer tonality body. And while both have a clear detailed treble, U12t has more sparkle in comparison to a more natural tonality of Duo’s treble. There is definitely a noticeable difference in weight between DD and BA bass, but what stood out the most for me was mids/vocals. If you want a lusher fuller body tonality, Duo is a great choice, while U12t delivers leaner and more detailed mids/vocals.
Duo vs CFA Solaris 2020 – Gotta remember to adjust the volume in this comparison, due to Sensitivity difference I had to lower the volume by about 17 clicks when switching to Solaris. I few people asked me to include this comparison, though these are quite different in every aspect. Solaris soundstage is wider with a more holographic imaging, while Duo does sound open but soundstage has more depth/height than width. Overall tonality and signature quite different as well, with Duo being warmer, smoother, and U-shaped, while Solaris being brighter, more revealing, and balanced with more mid-forward emphasis. Duo’s bass definitely scales up in weight with sub-bass rumble being more elevated and digging in deeper, and with a stronger mid-bass impact, making Solaris bass sound almost neutral in comparison. With mids, Duo has more body and warmer tonality in comparison to leaner body and brighter and more revealing upper mids of Solaris. And the same with treble, Duo being clear and more natural, while Solaris being brighter and harsher in comparison to Duo. So, again, if you want a more revealing micro-detailed holographic sound, Solaris is a better choice here, while Duo delivers and more natural, detailed, smoother sound with a more analog bass and more intimate presentation of the sound.
Source pair up.
In each source pair ups, I was using a stock 3.5mm cable and stock SpinFit eartips. Duo is not that hard to drive, but considering low sensitivity of 98dB and 9ohm impedance, I had to push volume 8-9 clicks higher relative to my other IEMs. No hissing was detected. For your reference, these are very brief pair up notes. And by brief, I just focus on any changes related to signature and general tonality, without going into too many details about technical performance difference.
Lotoo LPGT – laidback smoother natural tonality with a U-shaped sound sig (baseline).
iBasso DX300 MAX SS – stronger bass (sub-bass and mid-bass) impact with a little brighter mids.
Cayin N6ii w/R01 – similar to 3Max SS, a stronger bass and a little brighter mids.
Hiby R6 2020 – similar sound presentation as LPGT, smooth and natural.
L&P P6 Pro – similar to LPGT but with a bigger soundstage expansion and more analog tonality, along with improvement in retrieval of details.
A&K SP2000 SS – nice articulate bass and detailed natural mids, but treble in this pair up is a bit too bright and shouty.
Lotoo LPGT and L&P P6 Pro were my favorite pair ups with Duo.
As I was thinking about what to write in the conclusion of this review, I revisited my U18s write up from March of this year, and realized that I also offered my speculation about the picture of an open back grill IEM, keeping my fingers crossed for the next big flagship release. Maybe, this is just a part of our audiophile nature to wish for the next big thing. But in reality, we get excited just to hear the next “new” thing, especially from established brand like 64 Audio. And at $1,199, Duo is actually the cheapest universal hybrid IEM from 64 Audio that features all their signature tech, including tia, apex, and LID.
But what gets many excited about the hybrid design is usually a dynamic driver, and thanks to its 9mm bass DD, Duo can definitely satisfy a craving for that analog speaker like bass paired with a clear detailed tonality and extra sparkle of upper frequencies delivered by its tia driver. The natural, detailed tonality of this IEM has a non-fatigue relaxed tuning. And the open sound design with less isolation and minimum sound leakage, unlike typical open backs, makes Duo great for use in public places if you don’t need total sound isolation and instead prefer to keep awareness of your surroundings.
Actually, it doesn’t matter where you use Duo, indoors or outdoors, in public or in private. What matters is the laidback relaxed tuning and non-fatigue tonality with deep lows and clear detailed highs you can enjoy anywhere. Now, having said that, 64 Audio, we are still waiting for the next big flagship!