ETA Audio O2

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Headphoneus Supremus
The Best On-Ear Headphone I've Heard
Pros: open & airy, very resolving, great headstage, clean and full bass, most comfortable on-ear by far
Cons: upper mids/lower treble a bit too much on some recordings for my tastes (able to mitigate easily enough)
Many thanks to the people at ETA for organizing a loner for ETA's newest release, the “O2”. I imagine anyone reading this would be familiar with ETA by now, but there is lots of excellent information to be found on their website if you're not familiar with them ( / ). Like the Mini, this is an on ear headphone but the design is wholly new and created to maximize airflow, among other things. However just like the OG Mini, this was designed from the ground up by the minds at ETA. I'll add that like every headphone I've heard from ETA, I think they've done something special here. I'll try to keep it relatively brief but will gladly answer any questions I can.

Currently my audio chain is comprised of various WAV, FLAC & MP3 files played from JRiver on my refurbed HP Elite Desk via USB to a Schiit Bifrost 2 into either my Pro iCAN (1st version) or ZMF Pendant (also 1st version). The O2 is a 32ohm headphone, and the ifi was a wonderful match on low/medium gain. Interestingly where I found the O2 wasn't too sensitive for the Pendant, there was some slight noise detectable with no music playing (a common occurrence with the OG Pendant). Despite that the sound out of the low Z tap was truly engaging. Sadly I didn't discover this till the end of my listening, which is a shame because I really enjoyed the synergy there. I also experimented with various DAPs, all of which could drive the O2 without noticeable degradation. Keep in mind that although these are very efficient headphones that pair well with a quality dongle or phone, they do scale with "better" equipment IME. I have the word better in quotes because I found that it's more of a synergy than scaling up, so "better matched" might be more accurate. Either way I love the fact that I can enjoy these out of modest gear without feeling like I'm missing out. Puttering around the house with the O2 & an old Fiio X5 (2nd gen I think) was a real joy.

Comfort, Aesthetics and Build

Like almost all ETA Headphones I've handled, with the O2 build quality is quite solid if somewhat utilitarian. ETA utilizes 3D printed cups which may not look opulent, but to me they have an attractive vibe. Many are calling for ETA to produce products with more refined aesthetics, but I'm on board with sacrificing some looks in favor of saving a few bucks. They are still using a Sony headband, which I find to be perfectly adequate. An ETA developed and produced headband is confirmed to be in the works and this would likely dispel the last vestiges of DIY that seem to hang around their headphones. Earpads are of the snug over ear variety and posed no comfort issues during my time with them. It seems the aforementioned "E+" pads were installed and all listening was done with them. I found them more comfortable than any Grado-esque pads I've ever tried and I was able to wear them for hours with out discomfort. The headbsnd on these seem to have been pre-bent into an excellent shape at some point during (or before?) the loaner that minimizes clamp and helps with comfort I think.

Overall Sound

Like every other ETA headphone I've heard, I found the O2 to be a very engaging headphone, probably the closest to a "neutrally tuned" headphone that I've yet heard from ETA. I hear a very balanced tuning from the the O2, with good extension on both ends and a very slight mid-bass accent that play right into my preferences and doesn't intrude into the mids. Definitely some roll off in the sub-bass, but the reach down seems obvious to me and never left me wanting. Full, slightly dry midrange with a little bump somewhere around the 1-5Khz area as well that adds a bit more clarity and bite as it transitions to lower treble (sometimes a touch too much for my tastes), after which everything sounds pretty even to me, elevating incrementally instead of a downslope. Transients are the snappiest I've heard from ETA, staging is Larger than I've experienced with any of their headphones as well. Very good depth, decent width and imaging is slightly indistinct but not bothersome. Detail and nuances are readily apparent and approaching TOTL levels, even if just shy of those last few percentage points.

I'll intersperse my thoughts on sound with impressions with the Mini-S since it's the most comparable headphone I have on hand.

- Bass is fuller with the Mini S, which given the semi-closed nature isn't that surprising. "S" has lower reach to my ears, and a fuller mid-bass as well. O2 is definitely cleaner and tighter, it slams a touch harder as well. A matter of preference really as well as being dependent on the type of music being played.

- Mids are very similar with a bit more lower mid energy from the Mini S and more upper mid energy from the O2. I found O2 upper mids to be a bit too much at times with the Bifrost 2/ifi combo, but much less so with the Pendant. Weather that has to do with the Bifrost or the ifi or the combo itself I'm not sure, but the effect was definitely there. I was pleasantly surprised how much more in tune with my preferences the O2 was when used with the Pendant.

- Treble emphasis is more obviously pronounced with the O2, but I didn't find that aspect to be particularly fatiguing. I think after 2K or so, the O2 has more of an up tilt in frequency, and the "S" has a gentle downward trend. Plankton and detail retrieval would go to the O2, though not by a huge margin.

I found the O2 to have wider & deeper stage than the "S". I've always felt the "S" to be more on the intimate side, but never distracting. When placed next to the O2 the difference is more obvious. Being semi-closed, the "S" does feel more...well, closed in. The O2 is as open & airy as I've ever heard from a headphone. The unique design no doubt plays a big part here.
For my personal tastes, the Mini-S is closer to the sound signature I gravitate towards, but I could definitely be happy building a system around the O2, one that would mitigate the upper mid/lower treble emphasis. One that would likely involve tubes if the Pendant is any indication.

In the end, ETA has done a great job with the O2. At $600 (USD at the time of writing) I'd say the argument could be made for the O2 being a bargain, even if 6 Benjamins is nothing to sneeze at. Personal preference will (always) play a part here of course, but if under 1k is the market you're shopping in I highly recommend checking out the O2.
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