Archimago's Musings: MEASUREMENTS: Sennheiser HD650 (~2010-2012) and HD800 (~2010). A comparison of two "Reference Class" headphones, and a look/listen to the "Sennheiser veil / darkness". [Inexpensive 2TB SSD and inflation in consumer electronics...]
Sennheiser HD 650 Stereo Reference Headphones 508825 B&H Photo
Sennheiser HD 650 Review - RTINGS.com
Is Headphones Break-in Real? - Study by RTINGS.com | Page 3 | Audio Science Review (ASR) Forum