Sennheiser M2 AEBT - Wired + Foam Spacers

3mm thick, closed-cell 'craft' foam spacers installed inside the ear pads
Detail and treble are both lacking. The pads on these headphones get flat quickly after a couple years of use. This is proven by my previous graphs of the same headphone without foam spacers in the pads. Measurements in different positions were wildly erratic and inconsistent.
Now, with spacers, channel matching and measurement continuity are vastly improved.
I recommend everyone who owns one of these to add foam spacers inside the ear pads... and boost treble with EQ.