Got my HD600s a few days ago. Like Macc said, I was also disappointed when I first put them on. They sounded very dense, especially in mid/highs. However, I put it through some Source Direct albums on repeat for quite a while.... WOW.
The things just opened up! After about 4 hours of burning them in I noticed the bass seemed fuller. Yet, the mids still seemed a bit dense/closed. After about 8 hours, the cans really started to sound good. I stopped burning them in and started actually using them. I'm past 10 hours, probably 12-15 and they sound completely different than when I tried them on at first. Can't wait to get to the 20 hour mark
The things just opened up! After about 4 hours of burning them in I noticed the bass seemed fuller. Yet, the mids still seemed a bit dense/closed. After about 8 hours, the cans really started to sound good. I stopped burning them in and started actually using them. I'm past 10 hours, probably 12-15 and they sound completely different than when I tried them on at first. Can't wait to get to the 20 hour mark