64 Audio Duo Dual Driver IEM Review

64 Audio has been one of the most dominant audiophile brands this year now releasing their third major product this year. The U18s and the U6T made a huge impression on me with their ultra-detailed sound signatures showcasing high-fidelity without compromise. While the U6T was one of their most inexpensive models at the time, the Duo has come along to offer one of 64 Audio’s most economical to date. It’s sitting in the $1,199 price range, still being considered a high-end product, but for 64 Audio this is one of their most inexpensive UIEM to date. Let’s see exactly what it can do.

64 Audio contents

What You Get

  • Duo Universal In-Ear Monitors
  • 64 Audio Premium Leather Case
  • TrueFidelity Foam Eartips (S,M,L)
  • SpinFit Silicone Eartips (S,M,L)
  • Silicone Eartips (S,M,L)
  • Black Premium Cable
  • Round Sticker

64 Audio in hand

Look and Feel

Like most IEMs from 64 Audio, the Duo features the same style of housing but with a completely different faceplate. This is more in line with the U18s, which uses its faceplate to cover the entire surface of the earphone compared to a simple logo plate. However, the Duo’s design isn’t wholly for aesthetics, as the Duo features small pockets that allow for more airflow, shaping the sound signature further. There are only a few other IEMs that take on an open-back principle but the Duo is the only one I’ve seen that takes advantage of the entire surface area of the front plate. With the addition of a silver outline, the Duo presents a classy design that is both stylish and protective.

As for its comfort, this should be more or less what you’re used to with 64 Audio. The spout is wide enough to support a larger variety of ear tips, and the Duo already comes with a wide selection. I used to think 64 Audio’s UIEM selection wasn’t very comfortable, but I feel like they’ve improved the ergonomic factor of the cavity with each release. For long sessions of listening, I think the Duo will prove worthy.

64 Audio spout


Being a lighter system, 64 Audio doesn’t stack as many drivers this time around. However, they still implement their excellent Apex and tia technology. The tia-balanced armature controls the highs, and the 9mm dynamic driver relegates the low end. With the Apex Core, the Duo has a more controlled airflow with minimal obstructions. A wave sync system was also developed to add more integrity to the crossover between drivers.

64 Audio grille


I’ve always been impressed with the level of clarity and spaciousness included in past soundstages from 64 Audio. Considering the Duo’s open faceplates, I was expecting something great here and thankfully 64 Audio didn’t let me down. I felt a consistent openness with the Duo, creating a semi-holographic sound field that showcases complex imaging and identifiable layers between instrumentals, vocals, and sound effects. It’s rare for an IEM to display such an immersive sensation, but that’s not the only trick up its sleeve.

The overall size of these elements appears big, making for an incredibly grand stage. With help from certain aspects of the frequency response, the soundstage is heightened with quick and clear resonances that expand the scope of some tracks significantly. Huge orchestral scores will sound up to scale, and progressive rock odysseys will capture the proper sphere of musicality. I loved to just hear tracks dance around my headspace not only left and right, but forward and back. I’d equate this soundstage to a large oval, that performs with depth and accuracy to each mix.

Low End

For the Duo it’s all about the sub-bass for me. I can’t remember the last time an IEM vibrated with this much smoothness and depth. Listening to Colin Stetson’s rendition of “Sorrow” you get a meaty extension of the tracks droning low brass, which resonates through the sound signature with a deep tone that feels like it emanates from your chest. The rest of the bass timbre is very effective in providing great punch and impact to the frequency response. Electronic tracks from the likes of CHVRCHES will provide fast bass synth tones that will lift the instrumentals with a high amount of drive. This booming tonality is helped by a clean timbre that helps accentuate these frequencies without muddying them in the mid-bass.


I believe 64 Audio has a knack for implementing a spacious and articulate midrange to a majority of their IEMs. The Duo continues that notion by delivering a detailed response, especially when it comes to the upper mids, but I wouldn’t consider it very full. Some low-mids felt a little recessed in some areas, keeping the timbre from appearing richer. It’s hard to say if this was a response 64 wanted to avoid, but I felt more low-mid resonance would have added a bit more definition to an otherwise crisp timbre. Vocals and other high-mid instruments receive impeccable resolution, showcasing fine detail with an extra layer of texture to complete the timbre. Female vocals and high strings are a real standout.


There’s a mixed response coming from the high-end of the Duo. While some frequencies are textured and detailed, some of the tonality can verge on bright. The Duo won’t come close to harshness, but some sibilance can be heard at times. Sometimes this brightness is quite welcome, highlighting sparkly details and whispy cymbal crashes. However, this timbre isn’t consistent and has the chance to create a shimmery quality that can be hit or miss depending on the track.


While the Duo has a few characteristics to get past in its sound signature, this IEM still reaches quite the heights. Its soundstage is breathtaking at times, communicating complex imaging with exceptional clarity. The bass and especially sub-bass is incredibly textured and deep, hitting you with a feel so rare in most IEMs today. There’s less balance here than in some of their other models but still displays a great timbre overall. For its price, the Duo is certainly unique and worthy of being in 64’s line of earphones.

Pros  Cons
  • Excellent soundstage
  • Deep bass
  • Most affordable from 64 Audio
  • Crisp vocal response  
  • Style 
  • Comfort
  • Inconsistent treble

The 64 Audio Duo is available at Audio46.

Compare the ranking of various headphones, earbuds and in-ear monitors using our tools.

Discuss this, and much more, over on our forum.

MAJORHIFI may receive commissions from retail offers.
Previous articleiFi Launch Pro IDSD And ICAN Signature Editions
Next articleiFi Pro iCAN Signature Review – in Depth
Alex S. is a sound designer and voice-over artist who has worked in film, commercials, and podcasts. He loves horror movies and emo music.