I'll know more once I get back from Montana.
I am eagerly awaiting for your visit to BIG SOUND 2015 OMG and the write up to follow.
Last weekend I tried to replicate Tyll's shape but with my own twist. It seems like the thin Creatology foam plus polyester felt works well in a thinner ring – if you make it thicker it can over dampen the drivers and mess with the sound stage (from what I read on Tyll's writeup).
So I cut out a tapered ring, where the back (where the trapezoid connects) is 10mm wide, then near the front it tapers down to 4 or 5mm. I used the same trapezoid shape.
It sounded good but it looks like V2 of the mod introduced the layer of rug liner around the rest of the ear cup. I cut up the provided shape from the v2 mod PDF and tried to stick it in but it wouldn't fit. Clipping the rings in half made it so they fit PERFECTLY over the mushy metallic material, and do not cover the foam+felt at all.
Lastly, the HD800 has plenty of treble (to my ears) and it seems like the original liner helps reduce the 3kHz attenuation (can be seen in the original HD800 vs original no liner plots) so I put the liner back in. Also I am super paranoid about ruining the driver, so the extra protection is nice.
Ohhhh boy oh boy oh boy do these HD 800s sound good. Bass actually has that low end THUMP. Songs are still quite detailed and instruments are well separated spatially, but that ear-piercing peak at 6kHz seems to be tamed. I can actually listen to my most music without wincing. Before I felt constrained to only the purest of the pure recordings and that got old kinda fast.
Thank you for your work and everyone else who has contributed to this mod. Great stuff.