KillerTzhMany in the audiophile world believe as a headphone has music or "noise" played through them they "break-in" so to speak. Many time people report improved bass... tamed treble etc... Obviously your mileage may vary... you may notice no difference in the sound over time, or you may notice some difference. IMHO it is more placebo than anything else, but to each their own
KillerTzhI never believed in burn in till I owned a Sennheiser PC-350 headset. It was one of the worst sounding headphones I have ever heard and I was very disappointed with them. However after about 40-50 hours of use, the sound signature really did start to change drastically. And later on when I did a mod to add a couple ports to them to bring up the warmth, the headset became my favorite headset to date. Pretty incredible change from at first when it was my most hated headset. lol.
wontonotnowThe changes I've noticed in headphones are more to do with the pads wearing in more than the drivers, although anything that moves is subject to a wearing in period. I don't think it's really that noticeable though. That's my take anyway.
I had a pair of Klipsch S4s that I didn't like at first, but came to love. I thought it was burn in. Turns out I'd just gotten used to them. After leaving them for years and coming back I found I wasn't so keen on them again...