Edit: This thread was created to address the issue of irrelevance of disbelief in specific burn-in discussions that are found in the headphone forum. Somehow, it has been moved to the science forum (most likely because someone requested it) Thus, any confusion as to why I said what I said may arise as a result.
I'm going to make this as short as I can.
First of all, there have been a number of experiments in the last few years, both subjective and objective, to show that burn-in is a real phenomenon (at least for dynamic headphones with voice coils). You can easily and readily search for them and read them in your own time. At the moment, I can at least think of two, but I think there are others. One measured the tangible differences in frequency response between the two pairs (from a short while ago at head-fi), and another was done earlier this year by a couple of guys at innerfidelity in a double blinded test.
Secondly, although no definitive or 100% conclusive proof has been provided as for now (the reason why you are still skeptical, unless you didn't read the literature aka didn't do enough research), the consensus is that there is statistically significant evidence for burn-in. If you had known how many natural and social sciences use statistics as proof almost for everything, I'm sure you wouldn't have been as skeptical as you are. Not only mathematical and logical proofs can prove something, statistical proof is also scientifically based and is the reason for our current knowledge.
Thirdly, think about how we can never know for sure the sun will rise tomorrow morning, but we believe it nonetheless because it is statistically likely (with a p value asymptotically close to 1) that it will rise based on evidence in the observable period of time. There are many other examples that we take for granted when it comes to belief, like how the banks will give you back your deposits with whatever interest you're entitled to.
Last, definitive proof is not possible for this kind of test unless we can replicate an identical headphone at the quantum level or atomic level, which is quite some time away in our lifetime. Most, if not all, scientists agree that when the experiments are done right and the protocols are followed (like having good control subjects) the conclusion will be admissible. By the same token or in your (you, as in those who need impeccable evidence) own reasoning, you shouldn't believe 99% (100%?) of what you have been taught in high school and university about the world, because none of that knowledge was proven with "perfect" controls and under "perfect" conditions. Do you think you know almost nothing due to the lack of perfect evidence?
Still not convinced? That's okay. Just don't go to every single thread that's related burn-in and advocate you disbelief, unless the thread is asking specifically for your opinion on whether burn-in exists or not; or whether burn-in is psychological or not (almost always not the case here). That's like non-audiophiles (no, I don't mean average consumers, because I assume people who come here WANT to know more about audio-related things) come to head-fi uninvited and go to every single thread about audio gear and advocate their disbelief. How would you feel if they did that to us here?
Hopefully, this won't be seen as trolling as I (and maybe other like-minded people) just want to have some peace when discussing topics like burn-in. I personally don’t believe uber expensive cables or uber expensive amps, but I don’t go around to all the threads about them and tell them how it won’t matter. (So yes, I practice what I preach) Surely, you can understand my sentiments, given the elaborate analogies and so on. If I'm the minority here, that's cool. But that won't change the fact that I'm still annoyed about it. While majority does rule but it doesn’t necessarily mean that they're right anyway (the prominent example of the Nazi regime in Germany comes to mind).
I have nothing against your personal belief (as long as it is not about killing or harming another person); it does not concern me whehter you believe in burn-in or not.
Update: Here are some links to subjective and objective tests or experiments for those of you who don't like digging. Don't hesitate to contribute to this list. A caveat - this is not meant to be exhaustive, but just some reading materials or resources for skeptics and non-skeptics alike.
Edited by kingpage - 11/16/11 at 5:00pm