Difference with the HD650 (original) vs HD650 (2019) : r/headphones
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 – Thomann United States
Sennheiser HD 650 + Individual calibration | Without Software – Sonarworks Store