The headphone comes with a two-year, parts-and-labor warranty; repairs are handled in Beyerdynamic's New York service center. Customers must supply a copy of the original sales receipt or proof of purchase to the service center to make a warranty claim.
The T90 sounds accurate and imparts less of its own sound on the music than most headphones, including a lot of audiophile models. The purity and clarity of the sound is astonishing, you can hear "into" recordings with rare precision. Lesser headphones smear those sonic details and homogenize the sound more. The T90's sound presented a clearer view. Some headphones with above-average clarity such as this have a lean tonal balance, but the T90's sound, from top to bottom, is neutral. When the music has a lot of bass, the T90 doesn't hold anything back, but it's not the sort of headphone that adds extra bottom. V-Moda's M 100 does; it supplies low-end fullness even when the music doesn't really have a lot of bass.
It's an expensive headphone, so the first question is, what can the T90's deliver that you can't get from a more-affordable audiophile design, like the new $399 Yamaha PRO 500? That headphone's sound is brighter and more immediate, the T90 is more expansive and refined. When listening to acoustic jazz or classical music, the T90 sounds more like being there at the concert. The PRO 500 never lets you forget you're listening to headphones, while the T90's open quality is more like listening over speakers; it's less in your head. The PRO 500 had fuller, though significantly less well-defined bass.
I next compared the T90 with the $1,000 Sennheiser HD 700 headphones, and noted the Sennheiser was more dynamically alive and detailed, and produced a broader and bigger sound field. The T90 countered with a richer, more inviting tonal balance, and better, more powerful bass. There was no decisive winner, just two headphones with different strengths and weaknesses, but the T90 sells for one-third less than the HD 700.
The T90 plugged into my iPod Classic sounded acceptable, but the bass was lightweight, and the headphone couldn't play all that loud. That came as no surprise as the T90 was never intended to be paired with portable devices; it's a stay-at-home design. The T90's uber-resolution won't be kind to the sound of low-bit MP3s or iffy streaming audio sources, but it will bring out the very best sound from well-recorded FLAC files, CDs or LPs.
I watched a few movies on my desktop, using a Red Wine Audio Corvina headphone amplifier. The T90's home-theater skills are first rate; it served up oodles of detail, a wide-open soundstage, and exceptional comfort over the course of a long movie.
The Beyerdynamic T90 is expensive, but for well-heeled audiophiles the price will seem reasonable. I know of no other less-expensive headphone that can match the T-90's combination of comfort, sound, and build quality. Perhaps the biggest downside to the T90 is that it's not well-suited to portable use, but few full-size, audiophile-oriented headphones are. The T90 is best savored at home, plugged into a high-quality headphone amplifier or AV receiver.