Revolutionary open back headphone design?

Axel Grell is the legendary engineer behind some of my absolute favorite headphones, including landmarks like the Sennheiser HD600 and HD650. Lately, he has been using his own brand to test out some... outside-the-box ideas.

The new Grell Audio OAE2 ($599) is the direct follow-up to the original OAE1, pursuing the exact same set of unconventional mechanical concepts: extreme acoustic openness, and placing the dynamic driver very far in front of the human ear. While OAE2 improves upon the original in several key areas, it remains one of the strangest, most unique headphones I have ever encountered.

On a physical level, the OAE2 features a lovely, somewhat retro-futurist aesthetic that looks quite nice without making you feel like an alien when wearing it. It offers full cup swivel, allowing it to lie flat inside its (admittedly, gigantic) carrying case.

Ergonomically, Axel fixed the main issue of the original by offering much better arm extension. It easily accommodates larger-than-average heads—both Cameron and I can actually wear this one comfortably, whereas the original wouldn't even fit Cameron's head. However, the headband padding is passable at best; the surface area is somewhat narrow, meaning those sensitive to top-of-head hot spots might experience some fatigue.

Theory

The core theory behind the OAE2 is dual-pronged: it aims to provide as open an ear chamber as possible, while also offering a tuning profile akin to a front-biased sound field, mimicking the experience of sitting in a room relative to a pair of stereo speakers.

By pushing the drivers forward and away from the ear canal, the ear remains completely unoccluded by the driver housing, resulting in an incredibly open acoustic environment, and importantly, producing the frequency response cue similar to what the ear would receive from speakers at a distance...

...or at least, that's the hope. This doesn't actually work for me very well.

While I deeply admire the ambition to break conventions, this is a design philosophy I seriously struggle to get behind for multiple reasons... not least of which is that the headphone does not actually fulfill the treble criteria necessary to even approximate the timbre of a front-biased sound field.

But also, wearing headphones means you are wearing a sound helmet. Without active head-tracking, when you turn your head, the sound field moves directly with you. Your brain receives the exact same fixed frequency response at all times, meaning it lacks the dynamic situational and directional cues—to say nothing of the lack of reverberation or crosstalk—required to localize sound out in front of you.

Axel’s goal here isn't actually about generating an artificial soundstage, but rather seems to be about capturing a speaker-like timbre... but unfortunately, the real-world execution introduces a massive amount of acoustic volatility.

Sound

Up until about 6 kHz, the Grell OAE2 is spectacular. The bass is beautifully extended, solid, and punchy without ever bleeding into the lower mid-range or obscuring clarity. The midrange itself is phenomenal, completely fixing the dark, overly shouty character that plagued the original OAE1. If the response simply continued on this trajectory, it would easily be one of the best-sounding headphones on the market. But past 6 kHz, things go completely off the rails.

If you look at conventional measurements taken on the B&K 5128 test fixture we use, the graph shows a massive, deep hole in the treble.

However, when I measure the OAE2 on my own head using in-ear microphones, the reality is almost the exact opposite. Because the drivers sit at such an extreme, distant angle relative to the ear, my individual anatomy completely alters the high-frequency response vs. what we see on the measurement fixture.

On my head, that supposed treble hole turns into a massive, sharp railroad spike right between 7 kHz and 8 kHz. This creates intense, immediate sibilance, aggressively highlighting the harshness in vocal consonants like S, F, and T sounds. It makes the overall listen incredibly bright and incisive, and certainly unlike whatever speaker-like timbre was originally intended.

Conclusion

The Grell OAE2 is an undeniable improvement over its predecessor, delivering truly awesome bass and midrange performance. But because its unique acoustic design makes the treble response entirely dependent on your specific ear shape—but not in a way that mimics speakers, or anything good sounding—it is completely impossible to predict how this headphone will sound to you based on industry-standard test fixtures graphs alone.

It is an admirable, highly intentional break from convention, but the severe sibilance on my head makes it a struggle to enjoy, and the design/theory while novel is the definition of risky.

For me, the OAE2 lands a 5.1 out of 10 for sound quality, bumped to a 5.3 in overall score due to the solid comfort on my head. Because it is so uniquely sensitive to positioning and anatomy, this is the absolute definition of a headphone you should never blind buy. Try to hear it in person first, because for some, it might be great—but for others, it will just be uniquely strange.