That doesn't happen based on any of my experiences or anything I've ever read. It could be your source, amp, DAC? I've never seen headphones adjust that much over time with any quantifiable data whatsoever. The TH900s are horribly V or U shaped and that's the biggest reason I eventually sold them (that and the tizzy treble had me avoiding so many recordings).
2/10/17 at 8:00pm