yes, you need to burn in or run in... but that's to reach
100%...
when you first bought it, you should be able to have around 50-70%
.. and hope for 100% after burn-in period..
if you cannot tell the difference, why buy? it's either your ears
cannot make the difference or the earphone just damn right
lousy...
but i know sennheiser is a very good brand..