I love this new model from Audio-Technica's growing line of professional studio headphones. It features open-back earcups housing proprietary 45 mm drivers, and a unique headband with spring-loaded "wings" that self-adjust the fit. It's by far the lightest and most comfortable circumaural headphone I have ever worn. The earpads are covered in a breathable microfiber fabric that remains plush and cool, and there's just enough cushion to keep the drivers close to my ears for maximum fidelity, without earlobe contact. Being the gear geek, I appreciate the design of the Y-cable that plugs into the earcups. Each of the cable's earcup ends has a turn- to-lock, three-conductor TRS plug, so it doesn't matter which plug you use in which earcup jack; each receiving jack connects to the correct conductors for its respective left or right signal. Ironically, the headphone looks perfectly symmetrical, so the only way to tell the L/R assignment of the earcups is to look carefully at the inside of the headband for near-invisible markings identifying the sides. (I ended up placing a sticker on the right-hand side of the headband.) Also, only one Y-cable is included, and it's over 10 ft long, which is great if you're sitting in your favorite La-Z-Boy while listening to your hi-fi, or adjusting a compressor in a far-away rack against the side wall of your control room, but my preference is for a cable half that length. The only included accessory is a polyester-fleece carrying bag.
Overall, I would characterize the sound of the ATH-R70x as warm and inviting, but with plenty of honest detail. Low-frequency extension is exemplary for an open-back design, and I can clearly discern fundamental notes down to 22 Hz. Some distortion is audible at these extremely low frequencies, but I hear far less distortion in the ATH-R70x than in my open-back Shure SRH1840 headphone [Tape Op #89], particularly below 34 Hz. Moreover, the ATH-R70x's distortion is devoid of high-order harmonics, so it's less distracting, and deep bass notes don't sound falsely clicky. Moving up the spectrum from there, the volume takes a shallow slope up to 83 Hz, then tilts smoothly downward, contributing to the warmth I hear. Importantly, driver damping is well controlled, so there's very little distortion, ringing, or time-domain smearing in the lows and lower mids. A 3 dB peak at 3.5 kHz is followed by a -3 dB trough at 4-7 kHz, with some ringing at both 3.5 kHz and 8 kHz. Above 12 kHz, the extreme highs are gently tamed, but high-frequency detail is still there, thanks to good transient response and very quick settling time. Imaging is precise, with a strong phantom center surrounded by a wide soundstage.
Keep in mind that our individual head and ear shapes will affect how headphones sound, so what I hear in the ATH-R70x may not be exactly what you hear; but my listening notes should give you a general idea of what to expect. Also, don't let any of the numbers above scare you, because the peaks, dips, resonances, and distortions you might hear in high- quality headphones are far less consequential than the substantial blurring and inaccuracy caused by speaker-room interactions in all but the most perfectly treated rooms. My tests were done over a month's time — not only performing mixes and listening critically to familiar music (including songs I had mixed prior), but also listening to individual instrument sounds as well as test tones and impulses.
I'm not a fan of lifestyle headphones that emphasize bass and hype the highs. In contrast, the sound of the ATH-R70x is relatively neutral and absolutely unfatiguing, even for hours at a time. At $350 street, the ATH-R70x is not an impulse buy, but it's more affordable than many "luxury" headphones. I really enjoy listening to music on "open-air" headphones, and I own many models, going all the way back to several Sennheisers that I purchased in the '80s. But the ATH-R70x is the first open-back headphone in my collection that I would be confident using alone as a mixing reference, without a second closed-back headphone or a well-tuned subwoofer to inform me of the lows that would otherwise be missed or misrepresented. Consequently, this is the headphone I take with me between studio and house.