no ja som si tiež myslel, že je to o zvyku ucha na zvukovú charakteristiku. potom som to našiel v jednej recenzii spomenuté a začal som hľadať.
toto mi prišlo také najzrozumiteľnejšie:
"Burn-in is the process for exercising new audio equipment. Most headphones require at least 40 hours of burn-in time to reach their optimal performing state.

The main purpose of the burn-in process is to loosen the diaphragm of a newly crafted headphone and to stress the headphone driver. Most audiophiles agree that the sound quality will be noticeably improved after burn-in. "

http://www.jlabaudio.com/burn.php

poprípade: http://www.head-fi.org/t/56744/headphone-burn-in-faq