but yeah at least the pads make burn in real for headphones. but I wish I had some better measurement gears to test things "for real".
The difference was way too obvious to be caused by pads. Still I listed pads explanation for completeness. I might take them out and test in parallel with the same pair of pads, if you nag me enough.
you're bringing a special case, you could try with little time passing which is a huge improvement and makes me trust that you really heard a difference. not something I believe for too many people when hey talk about stuff changing withing months. memory is just not that good.
but the problem with 2 pairs is that it adds one new variable. they could sound different simply because they're different pairs and manufacturing precision isn't great enough to give the exact same result all the time. I usually get somewhere about 2db variation between left and right ear, and looking at this http://www.innerfidelity.com/headphone-data-sheet-downloads , I'm not alone. so if they fail to do both ears, imagine that they must at least fail as much from pair to pair.
or you can just take all the models where Tyll measured 2 different copies, the differences are there and in magnitude that clearly can be audible. the real question is to know if it comes from burn in, manufacturing precision, the way the headphones were put on the dummy head, the calibration of the dummy head maybe changing a little with time, the temperature and humidity for all I know. it matters, I doubt that it matters audibly, but it's measurable.
and it's probably a mix of all those stuff. I'm not saying burn in doesn't exist(even if I would rather call it wear), there are mechanical parts, so they will change with time that is for sure. what I find weird is how people can claim they heard burn in specifically, when there are so many variables, + time, + how we have extra focus and perception when we just got our new toy, +the time to get used to put it in place, and how much the frequency response changes with placement... how can anybody be confident enough to make burn in claims when it could be so many other things causing the change?
again your example is special, I believe the way you tested is much better, but it's hard to go with the hypothesis that the 2 pairs sounded the same the first day they were used. from my still small experience with measurements, I would bet the pairs of headphone are audibly different from the start more time than not.