Argue at will about the reality of burn-in, but these are the first headphone that showed burn-in is real.
After a couple of hours of play, I've never noticed much difference in any headphone, and differences could be chalked up to positioning, music choice, gaining familiarity, etc.
With these 1350's I noticed a certain dissonance with piano sonatas, usually in the mid-range or in a transition between high and low. Maybe this is the disconnect described earlier in this post. It was too prevalent and common to be related to a particular recording or era of recording. (The recording I noticed it on first, the first piece I played on the headphones was Uchida's Mozart Piano Sonatas.)
I knew about the importance of positioning as I had the T50's before these, so I couldn't attribute the problem to positioning. I just resigned myself to not listening to acoustic piano (as the headphones sounded great otherwise, esp. on jazz saxophones).
A few weeks, and anywhere between 20 and 50 hours of play, went by. I stumbled back into a piano sonata, one I know well and listened to frequently with the dissonance. Now, after burn in, no more dissonance. I played other piano sonatas and the sound was great.
This is first time I can definitively attribute burn-in to an improved sound, a particular improvement in a particular kind of music and instrument.
Otherwise, I love these for listening to classical or jazz music while reading, although I'm finding myself putting down my book more often now to listen to the music!
