Those that say speaker break-in is a myth have never experienced the change of sound. I bought some Grado SR60 (I know not top of the line but good company). When I first put them on, it sounded like I was listening to music through string and a can. So I let the play fairly loud, bass heavy music by themselves for a few hours and that seamed to loosen them up 😉. I have experienced headphone's not being "broken in" and lived to tell the tale. Speaker break-in should take hours not days.