First a note that all ratings are in the context of using that as a DJ headphone.  Going by audiophile standards it would be lower.   The reason I've emphasized use as a DJ headphone is because that's even what they were originally marketed as.  Can read all this on wikipedia but to summarize Sony has four headphones in this series: (from oldest to newest) MDR-V6, MDR-V600, MDR-7506, and MDR-7509HD.  The V600 was created in response to a lot of DJs using the V6.  It emphasizes bass and can be loud in the treble range as well.  This is intentional...