According to many sources, AKG recommends about 300 hours burn-in in order to really reach intended operating capacity with these. I've never seen a better example of the effectiveness of burn-in than with these K7XXs. I read about the efficiency of using "pink noise" to burn-in headphones on head-fi and it seems like a really good route to take for some. Companies and manufacturers have been using it with audio systems fo years. This is an excellent source with instructions on how to use it: http://www.jlabaudio.com/pages/audio-burn-in-download.