Ultrasone has done a proper job when designing the PRO900s. Everything right from their exterior design to the sound quality is really top notch. The sound is quite bassy but it is not over powered like on some other headphones. The only two problems I came across in my listening tests were the slightly elevated upper midrange which caused some tracks to sound a bit too sibilant for my liking. Another minor issue is the midrange, it is a bit on the recessed side which is quite a shame because the midrange is incredibly detailed and refined.
Kept short, the sound of the Ultrasones can best be described as involving and intense which is emphasized by their highly musical tonality. Because of their powerful sound they sound nice with a lot of different types of music, with rock you have the powerful bass and the composed midrange giving everything the right feel, with electronica the tight low end is both fast and apt enough to keep up with the pumping beats.