64 Audio Duo

Sound Analysis.

I analyzed Duo sound performance paired up with a neutral LPGT source while playing a variety of test tracks, such as Agnes Obel “The curse”, Sandro Cavazza “So much better” (Avicii remix), C-Bool “Never go away”, Ed Sheeran “Shape of you”, Alan Walker “Darkside”, Galantis “Hunter”, Iggy Azalea “Black widow”, Indila “Boite en argent”, Dua Lipa “Love again”, Counting Crows “Big yellow taxi”, Bob Marley “Jamming”, David Elias “Vision of her”, and Michael Jackson “Dirty Diana”.  I let it burn in for at least 150hrs before I started taking my notes.

I would like to start off by mentioning that due to lower sensitivity (98dB), Duo will require higher volume, about 8-9 clicks higher than my other average sensitivity IEMs.  It’s not a big deal, still easy to drive.  But when you are comparing and switching between different IEMs, don’t make the assumption that Duo will be OK at the same volume level as others.  The volume setting here is important, otherwise mids will be more recessed.  Push the volume higher which is still OK due to apex core design that relieves any sound pressure.

To my ears, Duo has a distinct U-shaped sound signature with a recessed perception of mids due to elevated bass and mid-treble.  The tonality is on a warmer and smoother side with a fuller body sound.  I didn’t find the sound to be micro-detailed or analytical, though tia driver helps to bring up the resolution.  And despite a warmer fuller body sound around bass and lower mids, the retrieval of details is good with the sound being clear, not muffled or veiled.  The overall sound has a relaxed, laidback presentation with a smooth, natural tonality, and a decent level of natural detail retrieval.

The bass has extra weight with a noticeable presence of extended and elevated sub-bass rumble that gives low end analog timbre, and mid-bass impact I associate with floor standing speakers.  Bass is relaxed, with average speed attack and decay, typical of DD driver, not too tight or articulate, but with a good control.  Sometimes extra decay of bass can contribute to thickness of lower mids body, but not in this case.  To my ears, I don’t hear bass spilling into lower mids.

Mids are smooth, detailed, natural, with plenty of body, yet without being muddy or veiled.  Especially when you focus on vocals, you can appreciate a natural organic tonality of both male and female singing.  So, lower mids have more body while upper mids are smoother and more organic. I usually look for sound separation and layering in mids, while here it is just average due to a more natural smoother tonality.  Mids are not lacking any details, just less revealing.  Also, when it comes to imaging, mids/vocals positioned farther out of your head, and sound a bit distant.  You do need to raise the volume to bring up mids quantity, especially due to lower sensitivity of Duo.  As I already mentioned, if you are switching between different average sensitivity IEMs and go back to Duo without changing volume, mids will be lacking resolution.  But as soon as you turn up the volume, they come alive.

Treble is the same way, need to pay attention to volume setting.  Duo is not for low volume listening.  Once you raise the volume to a more adequate listening level, the clarity and the sparkle of treble goes up as the tia driver starts to flex its muscle.  Here, lower treble is smoother, so don’t expect any harsh sibilance peaks.  Instead, the high definition and airiness of the treble comes from mid- and upper-treble extension.  Treble does pack some energy, but still sounds natural and with good non-fatigue definition.

Despite a more open sound, I wouldn’t call soundstage expansion to be super wide.  It is wide and definitely above average, but I hear more depth/height than width, with the sound surrounding you with more intimacy.  The open sound feeling comes from less isolation and zero sound pressure which makes you feel like you are wearing open back headphones, but with a benefit of hardly any sound leakage.  The imaging is good, not super precise due to more depth and less air between layers of sound, so don’t expect 3D holographic imaging.  But it is pretty convincing, nothing is congested, and it is easy to distinguish and position instruments and vocals.


Eartips selection.

The selection of eartips is crucial to any universal in-ear monitors and will affect the sound, especially the bass impact/quantity which depends on the seal.  Due to a large opening of my earcanals, I usually go for the largest size eartips to get a better seal.  Also, please keep in mind, eartips impressions are subjective and will be based on and relative to anatomy of my ears.

stock SpinFit CP145 – laid back smoother natural tonality with a more U-shaped sound sig.

stock TrueFidelity Foam tips – laid back smoother natural tonality with a more balanced W-shaped sound sig.

stock Silicone tips – these had a little bit of lift in bass and treble.

Azla Xelastec – more V-shaped sound due to lift in bass and treble.

Final Type E – similar to stock SpinFits.

Symbio F – similar to stock except treble was a bit brighter.

For me personally, stock CP145 and Symbio F were preferred eartips with Duo.


Cable pair up.

I’m aware that some people don’t believe in cables and have very strong opinion about it.  It’s not my intent to change those minds.  Instead, I’m just sharing what I hear during my testing.  What makes sense to me, a metal wire is a material with physical properties of resistivity, conductivity, purity, and unique geometry, all of which put together act as a filter between your source and earphones.  Variations of these physical properties can affect the conductivity of analog signal, resulting in a sound change, from a subtle to a more noticeable level.  If the talk about cables upsets you, please skip this section.  Otherwise, enjoy these short impressions.

stock to 64 Audio Premium Silver hybrid – the main change I hear is in mids, being a little more revealing and noticeably more forward.

stock to Eletech Socrates – very interesting effect of more elevated sub-bass and even stronger mid-bass punch and crisper treble.  The bass lift is actually not just subtle, but quite noticeable.

stock to PS Copper+ – another example of bass and mids lift, while treble remained the same.  Also, bass feels faster and tighter.

stock to EA EVO10 – in this pair up I hear sound sig being more V-shaped due to a stronger bass and lift in mid-treble.

stock to PWA 1960 2wire – I hear more clarity and resolution in mids/treble, but at the same time, bass is lifted and the tuning becomes a bit distracting.

I actually enjoyed 64 Audio premium silver hybrid cable pair up the most because it added some clarity to the mids and didn’t lift the bass like in pair ups with other cables.  Stock cable pair up is also good if you want a smoother and more laidback tonality.


Page 3 – Comparison, Source pair up, and Conclusion.

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