i'm still a relative newcomer to all of this, and had no prior experience with the concept of burning in speakers or headphones. i got my pro 900's about 2 months ago and after 20 minutes of listening right out of the box i was all set to return them. the sibilance. the earpads were covered with blood that was gushing out of my ears as they were repeatedly sliced open by the sibilance, even at lower volumes. it was awful. after some reading here, i was convinced to run pink noise through them, even though i scoffed at people's saying you need 400 hours of burn-in for ultrasones, especially the pro 900 because of the stiff titanium drivers. ~500 hours of pink noise at night, listening during the day later... the sibilance is literally gone. the same songs that made me wince, gasp audibly, and take the headphones off just a few weeks ago i can now listen to with a huge grin on my face. for sure, they are still bright cans, and i love them for their analytical, sharp treble. i enjoy a revealing can if you've got some decent source for it... and the sibilance is no more. the pink noise really worked wonders, and i couldn't be happier now with these. when i ran the pink noise through, i would set it to JUST over listening level. i do recommend it, and you most likely won't need such an extended burn in period for other headphones.