64 Audio Duo

Open for business!

PROS: smooth natural tonality, fuller body detailed sound, powerful bass, built-in apex, LID tech, updated cable.

CONS: universal only, poor isolation (by design).

The product was provided to me free of charge for the review purpose in exchange for my honest opinion.

Manufacturer website: 64 Audio.  Available for sale directly or from retailers like Bloom Audio.


Early this year when 64 Audio posted a teaser with 3 of their upcoming new IEM models, one of them got extra attention due to a design with an open mesh faceplate grill, leading many to assume a new flagship with a planar magnetic driver.  You can’t blame 64 Audio fans because they have been waiting for something brand new for a while now, and considering today’s market trend with prices going up exponentially, some were prepping for another mega-kilobuck release.  Part of their wish came true when 64 Audio introduced a brand-new Duo model, and many let out a sigh of relief when the price of this dual driver IEM was announced.

Without sounding too cliché, I honestly had no idea what to expect, didn’t know at all what is inside under the hood of that faceplate when Duo arrived.  I like surprises, and this was a pleasant one.  Now, after spending close to a month of listening and testing of this latest 64 Audio release, I would like to share what I found.


Unboxing and Accessories.

Not sure if 64 Audio is still in the process of tweaking the design of their universal IEMs packaging since Duo box is somewhere in between of Nio and U18s releases.  Here, it looks more compact, similar to Nio, yet the design is more “traditional” with exterior sleeve and magnetic flip cover box underneath, similar to U18s.  To get your attention, sleeve cover features a bold look of the mesh cover faceplate, while cover’s back has a CAD drawing of the interior design and key features printed underneath.

Inside you have a big foam block with a cutout for Duo and the cable snaked around it, as well as a round opening for a Premium Leather case with accessories inside.  It’s a nice quality leather case, great for secure storage or for a display on your desk.  Inside the case you have a plastic organizer for all the included eartips pairs, such as TrueFidelity foam tips (S/M/L), SpinFit CP145 silicone tips (S/M/L), and generic silicone tips (S/M/L).  Plus, you get a shirt clip and a cleaning tool, in addition to a round sticker with new 64 Audio label.


Since I haven’t tested U6t where it was first introduced, this was the first time I had a chance to see 64 Audio new Premium cable included with Duo.  This very low impedance cable, according to 64 Audio, measures 0.23ohms, features 4 separate silver-plated OCC copper wires, each with 26 AWG thickness.  64 Audio refers to this cable as 7x7x4 multi-twist where I just assume ‘4’ stands for a number of conductors.

The cable feels more durable, not as flimsy as previous stock cables.  It has a glossy rubbery thicker jacket, loosely braided wires between the plug and y-split, and twisted pairs of wires going to each earpiece.  No more dealing with a memory wire, here you have a pre-shaped earhook heat-shrink tube, and premium angled non-recessed 2pin connector housing with L/R letter indicator.


The compact all metal y-split and matching metal chin slider have updated design, and y-slit also features a printed 64 Audio logo.  Cable is terminated with a matching metal plug w/64 Audio logo, though the plug itself only offered in single ended 3.5mm by default.  In the past, many audiophiles have complained about stock 64 Audio cable.  This upgrade with a higher quality hardware and more durable build should make people happy, or at least happier.


64 Audio is very straight forward with their hybrid IEM naming, Trio – triple driver, Fourte – four drivers, Nio – nine drivers, and following the same logic, Duo – dual driver.  So, Duo is a dual driver hybrid design, featuring one 9mm DD low and one tia BA high drivers, along with a built-in apex module/core and LID tech.  The shell itself has a traditional 64 Audio shape which is nearly identical to Trio and similar to Fourte, including a bulbous shape of the nozzle base, so expect a similar fit.  And similar to those other IEMs, you will find a larger hole drilled at the bottom edge of the shell facing forward – a dynamic driver vent.  But you will not find apex module pinhole vent here.

While Nio didn’t have a separate apex vent in the shell due to the module being replaceable, both Trio and Fourte do have this pinhole vent since their apex module is internal to the shell.  In Duo description, 64 Audio refers to “Apex Core” where according to the design its faceplate features a perforated grill that leaves the shell of the IEM open to the outside for a less obstructed airflow.  The apex module, which stands for air-pressure-exchange, is intended to relieve air pressure in a sealed earcanal, thus you can see a connection relative to this new faceplate design.  And while apex module is not replaceable, according to the spec Apex Core system in Duo provides isolation of -12dB.


Actually, the faceplate design is quite complicated and consists of three-piece aluminum assembly.  You have an anodized aluminum grill fixture underneath of a black PVD coated stainless steel mesh, all high tolerance design.  The mesh is secured to the grill with a chromed stainless-steel bezel.  The aluminum shell itself has a solid build, and while appearing black from a distance, it has a very dark navy anodized finish when you look closer.  The tip of the nozzle has a protective mesh grill over tia driver to keep wax build up away.

And speaking of tia driver, which is an open BA driver used in majority of 64 Audio iems (usually placed in the nozzle), in Duo design they refer to it as a “complete Tia System to reduce unwanted resonance and distortion by allowing 9mm DD + Tia high driver to radiate into the single large Tia bore with no obstructions to the front of the driver”.  If I understand it correctly, the tubeless output of DD driver goes through open BA tia driver where the sound is mixed and comes out of the nozzle and into your earcanal.

Last, but not the least, Duo also features 64 Audio own Linear Impedance Design (LID) where despite a low impedance (9ohm), Duo should sound the same when paired up with different sources, regardless of their output impedance.  Just keep in mind, every source has their own sound characteristics which is going to contribute to the final sound you hear based on the synergy between IEMs and the source.  But the actual output impedance of the source shouldn’t have the effect on the sound.

And again, I want to mention that while this is supposed to be open sound design with a mesh/grill faceplate and only -12dB of isolation, there is hardly any sound leakage.  People standing a few feet away from me couldn’t hear any sound, and I even tried to hold my phone an inch away from Duo in my ears while recording ambient noise and didn’t hear anything.

The fit.


Page 2 – Sound analysis, Eartips selection, and Cable pair up.
Page 3 – Comparison, Source pair up, and Conclusion.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s