Speaker break in?

Does anyone know what the break in process is all about? Myth or fact? What is being broken in? Is there an optimum break in time? Low volume or high volume? I would appreciate feedback. My Revels (M20s) did sound better after a period of time. Why? The M20s sounded so much better than my previous speakers; I'm not sure if they were getting better or I'm just hearing more. Anyone with first hand experience? Set me free Audiogoners...
thanks in advance,