Closed-Back vs Open-Back Headphones: What Is The Difference?
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
Building YOUR Headphone IDEAS! Closed Back HD6XX! - YouTube