I got the idea from the Nautilus speaker, which as far as I can tell uses similar physics to dissipate the back wave.
It’s crazy how open they sound. Huge back volume stuffed with rockwool.
I have a bunch of other designs too, let me know if you want to see more or any questions.
Thanks for reading!
Ps- I’m also making a version that is an easy (no tools, easily reversible) snap-on mod for Sennheiser HD6-series. I’ll make the files free (if you don’t have a 3d printer you can order the parts from Shapeways or Protolabs or wherever) if you want to hear it on your Senn.