I think denser memory foam would better. I couldn't find my stash.I noted less of a dip with the foam compared to the fiberfill. Denser memory foam may help. A larger cup may also help. Let me try opening the vents...HM5 pads are better. More open. More air and space. They don't affect the 200-300Hz dip.Keep baffle partially sealed with the Creatology. I liked this the best. It sounded too shouty with the baffle windows open and too dead with them sealed closed with tape.Foam is still being used in front of the drivers. This actually has a measurable effect of taming the peaks slightly around the 10kHz area.
Really interesting results! (specially on the raw driver 3k dip removal.) Are the distortion measurements raw driver or fully assembled HP? The bass distortion is lower than the HD650 which I think use 40mm driver (though probably different material.) I wonder if the larger size driver trades off distortion on the bass for the tremble.
Distortion is taken on a solid plate lined with Creatology foam. A mic wand is attached to the plate and care is taken to ensure a good seal. The headphone was set to 90db SPL A-weighted with white noise.For the raw driver, I simply placed the microphone on a free-air coupler next to the baffle removed from the cups. So the measurement does include the baffle around the driver.
