White(silver) driver vs black driver ?
New pad vs old pad (
http://sonove.angry.jp/HD650_Pad_effect.html) ?
Were the White(silver) driver AND new pad type introduced at the same time ?
Was the production change done in reaction to address the 'veil' that had been reported in their flagship a long time ago ?
Could pads being compressed slowly changing the sonic signature and account for differences perceived between different 'samples' ?
Circumstances under which was listened (mind set) when we 'remember' how a headphone sounded when we heard headphone W a while ago connected to X with music Y at location Z at a specific time of day ?
A spread in production materials used during the long time it has been manufactured ?
Can someone actually tell which sonic effect is caused by what aspect or a combination of them and in what extend/ratio ?
Maybe just accept that even the same model headphones (manufactured over many years) just don't sound the same and include personal preference as well to account for which 'version' person A and person B finds to be the best sounding.
Personal opinion: I have the 'old' (black with old pads) and did find it an excellent headphone, never heard the new an old side by side in the comfort of my own surroundings.
I sold my HD580 as well.
Don't listen to the HD650 anymore though.