DIY Audio Electronics from Zynsonix.com: Cable and Mods for Sennheiser Massdrop HD6XX
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...]
Questions: Custom Cans copper mod HD650 HD600 HD6XX : r/headphones
Sennheiser HD 600 Series Mod - A Practical Evaluation Of The CNC Copper Mass Loading DIY Kit By Custom Cans • Music For The Masses
Jupiter Audio Research "J-Mod" (HD650 mod) | Headphone Reviews and Discussion - Head-Fi.org
Jupiter Audio Research "J-Mod" (HD650 mod) | Headphone Reviews and Discussion - Head-Fi.org