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64audio Duo Review : Sonic excellence


64audio, formerly known as 1964 ear is one of the oldest IEM brands I looked forward to, they had a V6 and Joker’s praise were more than enough to win my heart. Since then a lot has changed. This American brand has gone through a lot of changes. It still is one of the most renowned IEM maker in the world but their strategy has changed a few times. They still are making top of line custom IEMs, nothing changed there but their Universal strategy has seen some changes. Their budget offerings are no more, while the higher end IEMs have shown their domination. U12T and U18T are legendary, while the Trio has been doing good. And now, it seems 64audio wants a say at the Slightly less expensive price range. The Duo and U6T are the prime examples of this.

I found the Duo to be an unique kind of IEM due to it’s semi/open back design. Housing one DD and one Tia BA driver this IEM goes head on with Andromeda, Dorado 2020 and UM Mext. Priced at $1199 this IEM has only one color scheme. I will put it against the Dorado 2020, Fibae 4, Mext and Darn & co Tau Herculids if it arrives in time (it didn’t).

Get one for yourself from these links:


Duo comes in an unusually large box, strangely there isn’t a lot of accessories in the box except for the functional ones. The unboxing experience is straightforward. The firs thing that greets us is the IEM. The ear pieces are stuffed in foam while the cable is wrapped around a paper holder. One can find a few pairs of tips inside the box. Duo has a tip organizer which has 3 sets of foam, wide bore, and spinfit type tips, in S/M/L sizes. A cleaning tool, cable clip and a 64audio sticker are placed inside the carry pouch. There is no cleaning cloth or anything fancy in this huge box.


Duo comes with a very good 4 core SPC cable. This cable uses 26awg wires and 49 strands of wires in a single core. I find it to be better than what the UM M2 cable offers. This cable has a softer and a suppler feel to it and is less resistive too. The layer of rubber on it is of very good quality which feels soft to the hand too.

What I find odd is the quality of connectors used. Mine is 4.4mm and the connector size is huge and doesn’t have any stress relieve behind it. It definitely could have been smaller. The 2pin connector too is of plastic build, they could have used a more premium material or at least a different design for it. The Y splitter is small in size, the cable guides are relaxed and doesn’t exert much pressure on the ear.


Build quality of this IEM is as good as any of their flagship IEMs. If you have ever used a high end universal IEMs from 64audio, Duo duo shares the exact design and profile with them. This shell is made out of metal and is as sturdy as it gets. These ear pieces are reasonably small, they are not big and even if you have small ears, there might not present any fitting issues. This nozzle can fit T400 and T500 size tips, fitting narrow bore tips is a struggle and since this nozzle lacks a lip design using wider bores is a no go. Weight though is fairly low, it doesn’t feel heavy even after longer listening sessions and longer than usual nozzle helps with good stability inside the ear. Duo’s open back design with contrasty plates does give it an unique look but I fear that dust particles from my fingers can get caught in those tiny holes and might affect the performance of the IEM. Duo doesn’t have the provision to house the Adel module as the open back design makes up for more than that.

Ergonomics of this IEM is average at best, similar to Campfire Audio IEMs but a bit more comfortable thanks to the curvaceous design. I definitely would have liked a bit of wing on the inner side to provide better stability but it still is above average. 


Duo isn’t really moody when it comes to pairing with sources. I was unable to use it with mobile phones but with all the dongles and USB devices I have used Duo doesn’t pair badly with any of them. It does enjoy some power but this isn’t really needed to enjoy this beautiful sounding IEM. When provided power, it gains a good amount of stage expansion and a bit more body, especially with Micro Signature. I definitely can’t call this a source dependent IEM but do make sure that you use a decent source, if the source has problems, it definitely will reflect on the IEM. Interestingly doesn’t really need excellent mastering, it can mask some of the problems with bad recordings, making it a more forgiving and compliant IEM.


This simple hybrid IEM uses one DD and one high quality, Tia driver in each earpiece. But the drivers used are not the talking of this IEM. It’s the semi open design which takes the line light. This IEM simply can emulate an sonical experience seriously rare under $1500. One can definitely distinguish that the usual level of pressure is not building up, eliminating driver flex altogether. Strangely there is little to no leak.

Moving on, Duo has a typical hybrid sound with a slightly V shaped signature. It has a warm-ish feel in the lower end while the vocals are a bit less forward. Tonality is very neutral and the timber is musically inclined. Level of details and transparency is fantastic as usual.

In their words:

Duo feels light, leaving your ears feeling open and relaxed even for long listening periods. You feel simultaneously connected to your physical surroundings while you’re enveloped by music. Relaxed tonality lets you put them on and get lost. It’s able to present a non-analytical top-end while retaining air and sizzle. The vast open air sensation supports an unobstructed soundstage with impactful center imaging (unlike many other open back headphones) as well as no loss of bass. Duo effortlessly produces deep and rich low frequencies with plenty of sub bass.

I am using Shanling UA5 and iFi Micro Signature for this review. The IEM has spinfit or stock tips on it for the review.


Duo has an enjoyable lower end. It’s not boomy or heavy handed. Sub-bass extension is excellent with nice rumble while the mid bass is slightly less aggressive. It doesn’t have a big area of impact. It has the full bodied feeling. This can’t be labeled as a bassy IEM and I definitely can’t call this lower end tight either. It has the slightly slower decay letting the notes gain weight and punch while keeping the area of impact a bit more focused. It moves very good amount of air and the punch is mostly on the softer side. Level of details is very good and the layered feeling make it very enjoyable.

The only downside I find here is the slight lack of dynamics. Doesn’t matter what type of lower end notes it’s processing, most of the time it’s softer and rumbly. It doesn’t have enough accuracy at the upper bass region. If you love subs this is a good thing but I have to deduct some points for this lack of technicality and accuracy.


I have worked on handful of mid forward IEMs. This is not one of them. What Duo has is a more soulful sound. This mid range doesn’t have a higher level of energy but doesn’t lack with transparency while the decay gives it an theater type feeling. The transition from upper bass to lower mids is nicely done but the energy gradually drops a bit. This drop is not aggressive but perceivable. 

Vocals have nice texture, details and definition to them. Male and female vocals have very accurate timber but don’t expect a very throaty male vocals while the female vocals are spot on. They have exceptional accuracy and precision to them and have a very vivid feel to them.

Instruments on the other hand have excellent resolution and definition. They have good energy and are high on transparency. I wasn’t expecting this much of finishing definition and resolution from this IEM. The downside here are the slightly leaner notes in the upper mids which leads to cleaner and well defined notes and have a bit of extra sparkle at the finishing region. There is no sharpness to complain about since it can’t really manage to retain sibilant properties thanks to it’s semi open design.


From here on, the oh so popular custom made Tia driver takes over and it exhibits excellent capabilities. Out of all of its abilities, I like the way it keeps the natural attack and sparkle intact within the comfortable range. It’s calm, composed and still manages to deliver high level of details. It nicely maintains the energy gained at the upper mids till the mid treble region and then the energy starts to drop a bit. In comparison the UM Mext get a bit edgy with finishing and gets unnaturally dark in the upper treble region. Layering and separation are of the top quality. It’s even cleaner and more precise than the Mest mk2 too. The contrasty and crispy nature is more than enough to capture anyone’s imagination. Duo has the vividness which no other IEM has pulled off under $1500.

Treble extension is very good, there isn’t any other Hybrid IEM that does better than this around $1200 but one needs to keep in mind that there are a few EST and BA based IEMs (Shozy Pola39 and Elsa, Aural definition Pro 5) have the endless type of extension.

Are there any downsides here? Maybe.. The notes do not have a lot of height like Mext or Dorado 2020 and can feel a bit leaner too. Keep in mind that this leaner feeling is giving it the cleaner and vivid feeling. So, pick accordingly. To me, this is highly engaging as its technical abilities don’t let in a dull moment.


Stage size of Duo is bigger than average. It has a horizontal drop shape to it, slightly narrow and less tall near the head a wider and taller as instruments go further and well rounded at the end. Most of the instruments find their presence out of the head while some vocals and most of the lower end notes are placed inside the head.

Duo has one of the best imaging under $1500, it’s accurate and precise. This is because of its partially open design and slightly leaner notes. Slight bit of leaner notes give it the cleaner and more separated feeling. It just simply annihilate IEMs like UM Mext and Andro V3 into oblivion. Due to the open design its sonics are exceptionally developed and it’s ability of cue placement is top notch.


vs Campfire Audio Dorado 2020:

VS UM Mext:

Mext is the latest IEM form UM. It is a tri-brid but is mostly an hybrid which get some help from the Bone conduction unit. It has one DD and 4 BA drivers and is priced $100 less than Duo. Ships with a similar cable but is of the copper variant. I usually do not complain about size but the Mext is big and can be a bit uncomfortable inside smaller ears.

Sound wise, Duo is a more refined, detailed and precise while the Mext is a more v shaped and moody sounding IEM. Mext has mid bass hump, drop in in energy at the vocal region while the energy gained in the upper mids is carried over till the lower and mid treble region which drops sharply at the upper treble region. Duo has a more linear feel here with a less aggressive drop in the upper treble region. The biggest thing I didn’t like about Mext is its lack of micro details. It’s a musical and fun sounding IEM but at $1099 one needs at least as much micro details and transparency as a $200 BA based IEM (Akoustyx R220) but that’s not the case with Mext. Duo has this covered, and the bonus is its sonics and imaging. Stage too is bigger than Mext.


Duo is a very capable IEM, easily recommendable to someone who doesn’t want to sacrifice musicality or details. It has a very good balance of everything. It eats the Andro V3 for breakfast and holds its unique place in its price segment. Powered by its sonic abilities, it has one of most developed imaging under $1500 and renders very complex tracks with excellent cue placement. It easily is one if the most complete sounding IEM, an IEM which doesn’t lack with anything. Unless you already have a Dorado 2020 and UM Mext, the Duo easily walks into anyone’s inventory. The problem is once you start demanding extra bit of resolution or details from it, it isn’t the chart topper.

Look at it as a bit of musically tuned IEM which doesn’t lack with details but doesn’t get dead serious about accuracy or precision. It’s an IEM that is fun, but doesn’t let go of the details or clarity.



Suman Sourav Meher

Suman Sourav Meher

My humble audiophile journey started in 2010, when I was in college, where I fell in love with the elements, nuances, and variations of this mesmerizing world. The ability of tiny earphones to recreate amazing sounds made my bad days tolerable and good days better! Now I am a full-time audiophile with a preference for musical tracks, especially vocals and engaging ones. I must admit I am addicted, but not to drugs or alcohol, but to earphones. Come join me as I share my experiences, bad or good, and let’s have some fun!


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