For Audiophiles, By Audiophiles - ETA Mini O2 Review

The ETA O2 is a rare entry into the supra-aural headphone market, designed by enthusiasts with the goal of showing off what can be possible with the on-ear design.

4 months ago

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Kyle and I have been in and around the audio community for over a decade. Several household names today started when we were entering into the audio social space. Audeze, Dan Clark Audio, Schiit Audio, and ZMF; all of these companies started as we were new to the audiosphere. They were the underdogs at one time compared to Sennheiser and Sony.

Born from the community, ETA Headphones was created by Ev and Tommy. Now a three-person team of individuals whom we’ve shared social spaces with for a few years, ETA has released a handful of headphone models since their inception. Their mission to provide tailored headphones from the angle of “for us, by us” intrigued us to get hands-on experience with any one of their products.

We want to graciously thank Tommy of ETA for including us in a tour unit of the Mini O2. It's with great generosity that he and ETA allowed us to have it in our possession for so long.


I've bought my own pair of O2s after shipping the Den-Fi tour unit to Flux. The convenience of the form factor combined with the durability has given them a permanent space in my backpack. While open headphones aren't always the best choice for use outside, I do think it's nice to be able to hear my surroundings when walking around downtown or for quick errands, and for this use case, I don't ever wear them enough for the comfort to bother me.

Build & Comfort


The Mini O2 is an open-back supra-aural, or on-ear, headphone coming in at about 204g on my scale. For comparison’s sake, the Sennheiser HD600 and HD650 weigh about 260g.
The cable provided was the UPOCC Cable by Audiophile Ninja weighing in at about 56g with a tip-to-tip length of 52” or 1.3m. It is worth noting the cable listed on the website is significantly longer at 7ft or 2.1m.

I’d like to rip the band-aid off right now and say I’m not a fan of supra-aural headphones.
I’ve tried various Koss headphones with aftermarket comfort solutions in the form of pads and headband alternatives.
I could never get Grados to feel comfortable around my ears or on the head.
I feel my issue is that I’m more comfortable with a pad being around my ear rather than having direct contact with my ear. The phenomenon of discomfort also translated to other on-ear headphones like the Creative Aurvana Live as well as the Beats Solo 2.

I have had many sessions with the Mini O2 and while I don’t think it’s the most comfortable headphone for me on the ears, it is incredibly lightweight and doesn’t bother me on the top of my head. The headband is very much inspired by the Sony MDR-7506’s head cushion and height adjustment. Out of the 10 total notches for height, I’m at notch 6 with or without inserting an additional comfort pad.

However, the earpads prove to be my primary complaint with the Mini O2. The Ada pads contain a fabric that didn't gel with my ears, given the pressure points they applied. I never felt like I could be comfortable with the headphones in a longer listening session using these pads. I would soon be constantly reminded I was wearing a headphone, or that my ears/head weren’t a great match with the Ada pads. The E+ pads were significantly better in that regard for me, providing about an hour of use before I would want to take a break. The Ada pads sounded better to my ears than the E+ pads, but I appreciated the fit and comfort I could achieve with the alternates.

The cable from Audiophile Ninja is serviceable without any complaints. If you want a different cable from another manufacturer, try to avoid a heavy cable with the O2, as they are a very light pair of headphones.


I'm no stranger to supra-aural headphones and rarely found issues with comfort with anything other than the Audeze Sine. However, with the E+ pads, the metal grill of the driver presses on my pinna and after about half an hour, it's fairly uncomfortable. Since I've bought my own pair and am less afraid of damaging it, I've bent the metal adjustment to help significantly with comfort, but by "significantly," I mean an hour instead of half an hour.

Associated Equipment

Flux's Gear

> Qobuz and local files via Roon or HQPlayer on PC
> Dangerous Music Convert-2 DAC or Bricasti Design M1 SE
> Bryston BHA-1, Eddie Current Studio Tribute, or Zähl HM1

Kyle's Gear

> Qobuz and local files via Roon or HQPlayer on PC
> Accurate Audio B660 and USB to Fiber Converter
> Exogal Comet, Modded PS Audio DirectStream, or Sony WM-1Z
> Luxman L550A, Neurochrome DG300B, or Esoteric A100

Sound Impressions



The Mini O2 has an elevated bass region that I find very close to my bass preference target when I’m gaming or indulging in some of my vices. With all of my favorite headphones that I have at home, I always have to apply some form of additive bass shelf or peak filter via EQ. Thankfully, the Mini O2 serves me with enough bass below 100Hz that I can omit that common preference tweak. I’d like to applaud ETA for a headphone that outside of the upper bass tones bleeding into the mids a bit much for my preference, satisfies me in terms of overall quantity. For what kind of quality of bass I’m getting out of the Mini O2, I feel it has commendable punch and impact compared to most headphones I’m familiar with. I made sure that it wasn’t just my gear giving a helping hand so I swapped to an available JDS Labs Atom Amp/DAC stack and the O2 still exhibited substantial bass character compared to the difference between the signal chains.


The O2's bass changes character between my different amps to a degree that has to be heard to be believed. Off an Apple 3.5mm to USB-C dongle or my Sony WM1Z, the bass has decent punch but lacks the decay I would expect from a transducer that can hit as hard as it does. However, off my Luxman L550A, my ears literally vibrate with sub-bass. I've made sure this is not related to volume and in fact, the O2 out of the L550A continues to vibrate at volumes even 5dB quieter than the more portable sources. It's a fun trick, though I will say my Neurochrome DG300B amp seems to add some much-needed decay, at the cost of the visceral bass.



Before I looked at a graph of the Mini O2, I thought something was going on with the mids that reminded me of the HEDDphone One’s frequency response pattern from about 700Hz to 2000Hz. The fundamental frequency of vocals and instruments is pronounced more than some of the harmonics, creating a slightly reductive lens to which I heard certain albums I had previously discovered on other transducers. Pair this with the bass bleeding into the low mids, this reduced my use case with the Mini O2 towards an everyday headphone. Once I adjusted to the frequency response, it didn’t wow me when listening to tracks I was already familiar with on my most capable transducers. However, the Mini O2 did encourage me to discover more music, as I would eventually use a more preferential headphone.


It's inevitable that an on-ear design will be compared to a Grado at some point, as Grado is one of the few headphone brands that continues to focus on on-ear headphones. Luckily, I actually find Grados to be fun, so naturally compared the O2 to my RS1. While on-ear headphones usually have a bump around 2kHz, the O2's spike pales in comparison to the searing 2kHz peak the RS1 has. Unsurprisingly, the O2 is a lot less aggressively shouty than the RS1. The peak is slightly noticeable, especially if I've gotten accustomed my Caldera's sound signature, but I think the amount of shout is just enough to make driven music sound even more driven. I do agree with Flux's assessment that with the E+ cushions there's just a little more upper bass than I'd like, negatively impacting the midrange balance as a whole.



I can’t complain too much about the Mini O2’s treble. It doesn’t bother me with major peaks in my problematic areas at 8kHz and 10kHz. My issues with the treble reside with percussion and cymbals sounding a bit dull and muted and having some extra energy around 6 kHz. I feel it’s more of an issue of frequency response, further cementing that the O2 is not perfect for me in the treble in that regard.


Ditto--I do think I hear a bit of scratchiness in the transients that dulls out a little too much in the decay, possibly related to a relative lack of ear gain that comes after a mild peak at 2kHz. Treble measurements are not a great thing to count on, but I do think treble sounds slightly gritty.

Subjective Musings



The O2's timbre is in a similar ballpark to me as the Focal Elex. In this comparison, both are rough around the edges relative to perfect and would benefit from some informed source chain tweaks to help bring them closer to that ideal. The Mini O2 isn't similar to any headphones I own in this regard.

The Mini O2 is serviceable in the daily driver role I found myself using it in. I allowed myself to succumb to some brain burn-in and not be as bothered by its imperfect timbre. It was most tolerable with music containing instruments that weren't naturally sourced.

If I prioritized timbre in an open-back dynamic driver headphone, I would gravitate towards the Sennheiser HD600 or HD650 with new or minimally used pads.


I found the timbre to be somewhat strange. I haven't heard it in any other headphone before but I can't describe it as plastic (weak transients with fast decay and a slight "nasal" tone), or paper (sharp transient then very little decay). The O2 is more "scratchy" than anything. It's close to "paper-y" headphones like the Fostex TH900 or the OG ZMF Auteur but adds a hollowness to decay. "Wet" sounding amps like my DG300B does help with the hollowness but cuts more of the transients than I'd like.



For the price point, it’s solid. Minimal acoustic material damping in between the listener's ear and the headphone's driver benefits my interpretation. I hear the driver translating enough upstream information from the source chain that it’s not significantly below average. I feel there’s some information missing based on my recent experiences with speakers and in-ear monitors, but those are contrasted by completely different price brackets and somewhat irregular use cases.


I hear the Mini O2 adding a bit of emphasis to the macrodynamic side of my sound perception. I hear it being under what sets the macrodynamic standards for me with Audeze LCD4 or Focal Utopia where driver excursion hits a personal maximum for what I’ve experienced and still enjoyed.
Microdynamics on the O2 are decent. I perceive them being a little lackluster based on what I have around to compare it to (LCD-4 and Utopia) and I'd call the overall dynamic contrast good, if a bit middling compared to the flagship headphones I still own.


The Mini O2's stage is pretty good for a supra-aural headphone. I find some of it comes from the frequency response dip around the ear gain region to push some vocal overtones down into the mix. When using my Zahl HM1, I messed around with the Stereo Base control and added one step of its effect frequently while using the O2 to give it just a little more perceived width.


Compensated version of the previous measurement

Closing Thoughts


In 2023 and this first portion of 2024, I have listened to a dozen or so electronic music artists performing their live sets or curated setlists on YouTube in the time since first borrowing the Mini O2 from ETA Headphones. So many times, I put the Mini O2 on, and an hour or so goes by as I listen to a Boiler Room set and queue up another batch of tracks from a different artist. ETA Headphones unintentionally created a ripple in my personal life to finally discover music at a time when I was finding comfort in cycling through my own greatest hits.

The Mini O2 ultimately fulfills the role of a fun flavor headphone for me, even if it's not something I would consider the pinnacle of my listening ideals. I'd like to applaud ETA for making the Mini O2 the most capable on-ear headphone I have ever tried. The major caveat when it comes to any personal audio transducer is comfort, and my ears don't perfectly mesh with the O2 in that regard.


Like Flux, I think the O2 is an interesting flavor. It has all of the makings of a headphone that one would graduate to from a Koss KSC75 or Portapro. It's incredibly easy to drive, small enough to fold and put in a coat pocket, and has enough bass to counteract the inherent reduction in bass that comes with using an open headphone outdoors.

However, the one thing that detracts from the O2 more than the sound is something that is often overlooked by me: comfort. I never use the O2 at home because they're simply too uncomfortable for me to use for extended periods of time, even with my smaller-than-average flat ears. I understand the merits that ETA extolls regarding supra-aural designs versus circumaural (around ear) designs, but even the best sonics in the world wouldn't mean much if the experience is dampened from a physical perspective.

However, if anyone reading this happens to not have issues with the comfort, the O2 can be a very interesting, visceral experience.

Published 4 months ago


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