I changed the earpads on my HD 650 headphones in the 20s and it's like having brand new headphones (sound-wise)! They may be expensive for earpads, but as unbelievable as it may seem, they make a big difference. I had also tried imitation earpads, but they don't compare. The imitation ones had a thinner profile, which plays a big role in the sound result. At some point, I will compare them with a newer piece and I will come back with my findings.