I can't remember which but Grado recommends 100 or 200 hours of cycled break in if you speak to them. I've had a few pair and they all responded positively to a few additional high volume 8hr sessions after normal run in. Obviously don't break them but louder than you could listen. The diaphragm doesn't have a rolled surround and relies on the natural compliance and damping of the material that supports the armature.
7/19/14 at 10:32am