I was having an issue with my TH900s. There was a narrow range of frequency, somewhere within that of a tenor voice, which would linger a bit. It was not an echo, it was just a decay which sound very much like an echo. And it happened in one eat. If I reversed my headphones, wearing them backwards,the sound switched ears. However, if I turned the earpads 180degrees so that they were backwards too, the sound disappears. So now I always wear my phones backwards. And I keep the ear pads oriented to the ears a the are designed. I feel like the sound has improved slightly, and that odd echo which is not an echo had disappeared. Also I think they are more comfortable. They grip better.