So on my loudspeakers, Gedlee Abbeys, the designer used high density foam to reduce HOMs created by the large waveguide. I'm curious if this is the same issue we are seeing with headphones and if the same sort of foam could be used to make headphones sound more coherent. Most foam I've seen used is of a lesser quality type, I'd have to see where to get this stuff. Tissue degrades so I wouldn't choose that (and because of the issues mentioned a few posts above), but high frequencies are easily absorbed so there must be a better option available. I have a pair of K7XX I've hardly used so tempted to try out a few mods mentioned here. My experience with this sort of foam is that it diminishes the very top end a bit but creates better coherency and makes the sound more pleasing as those effects from sound radiating off of reflection points causes a lot of annoyance. Thinking of using something like 30ppi 4" open cell foam that many tried in econowaves. Anyone tried this on a headphone? What I'm curious to see is if the shape it's carved into can be tailored to an individual headphone. Good mod ideas so far.