BREAK-IN :
Break-in is a controversial topic that easily stirs up heated debate in any audiophile circle. Some people believe in it...others dont...still others believe in it to varying degrees.
I believe in it to an extent. I believe that break-in or burn-in improves the sound quality of any speaker, headphone, subwoofer because you are, in effect, loosening the suspension to its optimal conditions. Just like a car engine needs a few 1000 miles to settle down before you take it for its first service - a headphone needs to be broken in for approximately N hours (N depends on the headphone...its impedance...and its sensitivity levels) before it starts to perform at its optimum.
The best way to burn-in a headphone is :
Create a CD with audiophile test tracks. Some of the tracks you will use are :-
* White Noise
* Pink Noise
* Pure Sine Wave from 10 - 30000 hz
* 10Hz, 20Hz, 30...40...50...60..80..100...150...200...600...800...1000hz (for the bass and midrange response)
NOTE - the tracks should be free of square wave patterns...NO CLIPPING IS PERMISSIBLE!!
Now - set these tracks to repeat. Play them and listen with the headphones on your head. Raise the volume about 15% more than your maximum listening level (maximum level with which you can still comfortably listen) and set the headphone aside for about 100 hours. You can wrap it in a towel to drown out the noise

This is what I do and it works - dont blame me if you screw up.