BTW, pertaining to the OP. I've measured five pairs of HD800 with s/n's from the hundreds to ~15000. (I can't say for units s/n ~20+), but all of the HD800 basically sounded the same and measured the same, at least on my rig (despite provided Senn graphs.) Maybe, maybe one pair, Maxvla's s/n ~15k seems slightly warmer with less of a peak in direct comparison with two other pairs (Jason and Analmort's) we happened to have had on hand for that session. Even then, the measurements on Maxvla's pair did not indicate any significant differences which would explain this. The subjective differences between so called early pairs and late pairs can probably be accounted for as follows: 1) individual pair characteristics; 2) music being played at the time; 3) equipment being used at the time; 4) mood and/or developing tastes.
It's possible the later production pairs do sound different, but I haven't encountered this specifically with early s/n and late s/n pairs in direct controlled tests using the same measurement equipment, and same sets of ears, test tracks, and gear. Besides, if you've ever talked to a Senn rep, they will say the HD800 is neutral and perfect. One tends not correct neutral and perfect.
Edited by purrin - 1/24/13 at 10:27am