By drivers, i mean the diaprhams and speaker cones in the headphones.
They soften up, get looser, more suple. More suple means the driver moves easier and more accurately.
Like if you have a draw which isn't on runners, you have to pull it and then jag it side to side before it comes out and moves how you want. Alot of the energy you put into that was wasted moving the thing.
Then you do the same thing with a lubricated draw on wheel runners and it can slide in and out accurately and quickly with little effort.
Same theory with speakers.
They get better over age (to a limit) because they can move better, and they can respond better. Typically with new headphones, with sub 20hours of use (maybe 40hours on some headphones) they have very weak bass response and boring mids. This is why you must never judge a headphone until it is atleast 50hours used with moderate/loud listening volumes. They sound so much different after them hours, typically a lot better bass response and the high's are not as painfull on the ears.
You notice it alot more in some speakers and headphones than others. The most extreme case was my Shure SE530 earbuds. I tried them at first and they were horrible. i mean utterly disatrously terrible. They were the most tinny sounding, lowest bass output, stringent peircing high headphones i had ever heard (no exageration) they were worse than the stock iPod earbuds. Within the next 12hours (yes, only 12 hours) they changed into a thing of immense audio quality. Best bass in iem's (in ear monitors, aka earbuds) i have ever heard, they had such rhythm and tonality it has to be heard to be beleived.
Hope that cleared it up
I do hope you repped me for all this xD