@E_Schaaf - do you have documentation of your HE-4 mods? I got wind of them in another thread and, being a long time HE-4 owner, was curious what you came up with. Mine have been gathering dust over the years but quarantine has brought me back to headphones. Unfortunately, I'm more sensitive than ever to the sibilance on these. Any chance anyone has had luck mitigating this? I once played around with a passive resistance filter (thanks to advice from Solderdude) which helped reduce treble intensity: Blue: stock Red: filter to bump up treble surrounding the 8k peak in an attempt to flatten the response Purple: filter to drop treble Note: the 200Hz - 1kHz sawtooth region is the result of removing the star felt on the back of the driver (the only other mod on these headphones). This was much flatter with the felt still present, though I don't have that measurement on-hand anymore.