I do not hesitate to put a note in "Perfect" because it seems to lie in the same philosophy as the small Porta Pro: they both look a little sexy but its amazing that crosses decades and ways to stay ... a reference!
The Porta Pro has an excellent value for money but the ESP 950 is intended as a listening without compromise.
I have owned excellent headphone like the Stax Lambda Signature and I appreciated the delicacy of the high and the "open" side of the headphone.
But KOSS ESP 950 is a headphones frighteningly more uniformly over the entire bandwidth: not only the serious down very low but is extremely powerful!
The medium is just sounds very acute in place: the sound is clear, neutral!
I never listened to a headphone with as little distortion as many serious and pushing the volume.
He played in the same league as the Stax SRS and 007TII but KOSS is six times cheaper!
Always a brief reference for over 10 years is sold!