I just might do the earpad replacement measurement. I've got an old pair of 600s with mushy pads to use. Good idea.
662 hours is is almost a month. I just can't tie up my chamber for that long when there are so many headphones to measure. A perfect example of why I really can't do research.
Thanks for the comments!
I totally understand on the time thing - especially when half of that time the headphone is just sitting there, waiting to be measured again. I know you say you can't do research, but you've already done better than anyone can do short of the biggest audio companies and major research universities. It's excellent groundwork from which bigger studies could be developed, which is a big achievement in and of itself.
As for the 600 pads - I'm glad you like the idea; it'd be great to see what that results in. I was thinking about the different Grado pads, too, but figured that someone had measured them - you of course! I noticed that the link to the PDF for those tests is broken though: http://www.innerfidelity.com/images/Grado%20Headphones%20And%20Ear%20Pad%20Tests.pdf
Actually, the Grado pads switcharoo thing reminds me of the most popular HD 600 mod - taking out the foam clamped underneath the ear pad. That'd be something to consider doing too if you do in fact put the 600s on the test rig. Not quite related to the burn-in phenomenon, but interesting nonetheless.