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...]
OG models (JAR580/JAR600/JAR650)
Questions: Custom Cans copper mod HD650 HD600 HD6XX : r/headphones
NwAvGuy: Sennheiser HD 650
HD600 / HD650 CNC Copper Mass loading mod DIY kit – Custom Cans Shop
Sennheiser HD 650 Mod Compilation | Page 4 | Headphone Reviews and Discussion - Head-Fi.org
DIY Audio Electronics from Zynsonix.com: Cable and Mods for Sennheiser Massdrop HD6XX
Sennheiser HD 650 Mod Compilation | Page 4 | Headphone Reviews and Discussion - Head-Fi.org