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 HD650 Review (Headphone) | Audio Science Review (ASR) Forum
Sennheiser HD 650 review
Sennheiser HD650 review | TechRadar
Sennheiser HD650 Review (Headphone) | Audio Science Review (ASR) Forum
Review: Sennheiser HD650 – Answering Questions About This Perennial Classic - Headphonesty