In my more embarrassing years, I hugged some subwoofers. And when I first fired up the Ultrasone PRO 900 closed-back headphones, I felt that familiar husky frequency. The bass slam was real, even without a metal grill imprint in my skin. The response was boomy, even by Ultrasone standards (the company's HFI-780 was previously a bassophile's dark fantasy). However, left alone to a healthy 100-hour playlist, these PRO 900 cans settled into a character less about my initial imagery and much more about riveting imaging.
The PRO 900s were tested playing all manner of MP3s, Apple Lossless and FLAC files, SACDs, DTS 96/24 and 192/24 DVD-Audio (oh, even a few plain ol' CDs). Some artists analyzed included Depeche Mode, Delorean, Clark, Burial, OutKast, Björk, HEALTH, Can, Phoenix ... hell, even Paul Oakenfold's latest Perfecto mix; just because these plushy velvet ear cups are $549.95 doesn't mean audiophiles have good taste, and the 40mm mylar/titanium-plated drivers offered a physically involving, snobbery-repelling experience.
All sounds were auditioned through either a MacBook Pro/Native Instruments Audio 8 DJ outputting 96 kHz/24 bit or an Oppo DV-980H universal audio/DVD player paired to an Integra DTR-7.8 receiver. (The PRO 900 deliver 6 - 42,000 Hz, 96 dB max SPL at a relatively efficient 40 ohm impedance, so you can drive them with a laptop/iPod headphone output, etc. but a dedicated amp is recommended to resolve full details.)
“Boxy” does not apply to any aspect of the circumaural PRO 900; “extension,” however, is very apropos. The smooth lead in/lead out of transients, the directional cues, the airy soundstage—in these areas the PRO 900s shine. Tones reveal both proximity and extremities, rarely feeling congested. Mind, the PRO 900s are not neutral. Overall, there is a warm, rounded characteristic, which allows highs to avoid fatigue at the edges (note, however, these headphones are reasonably unforgiving of heavily limited/hot sources, so compress with caution). The mid-range seems mildly “recessed” at times, but with such prodigious bass and pronounced highs that isn’t surprising; more accurately, the mids aren't augmented, as these headphones are more deliberate than “forward.”
Isolation/clamping power is pretty good, so the PRO 900s would be capable for live tracking (assuming you can handle the potential damage stress). However, these really come across as comfortable headphones for mixing/mastering, for balancing cerebral and visceral in a more private monitoring solution. It aims squarely for the gut without neglecting the gilding.