When people say 'dynamic', I think they are actually talking about 'compressed'.
Dynamic would mean that the phone produces the loudest passages at a very maximum relative level to the quietest passages. That is, the phone has a very high dynamic range measured in relative dB (with the lowest amount of distortion).
I think HD 600 is incredibly dynamic. Most studio headphones that are drive very loud need to be dynamic (with proper amplification!).
How can you hear it? It plays the subtle parts very subtly and loud parts loudly, if one has enough of amplification (this is not a sideline to anyone, but we all know HD600 requires good amplification).
Is DT770 dynamic?
I don't have enough experience with it to evaluate it as a whole, but the very little experience I had with it on X-Can V2 was that with that amp it certainly did not sound dynamic to me.
Are AT cans dynamic? I only have a very short exposure to W100, but I think it plays being dynamic by having a bump in the c. 2-4 kHz region, making it sound like it's more alive and have a feel of dynamics.
In my opinion 'dynamic' (as a technical term, meaning relative range of loudness values) usually means completely opposed to what people mean when they say 'dynamic' (the perceptual description, meaning alive, scary, punchy, kicking or whatever).
After all, most people consider CDs that are compressed to oblivion to be the most dynamic, alive, hot and kicking. These kind of CDs have the most narror dynamic range and are by definition, not dynamic, but compressed.
Any thoughts?
regards,
Halcyon
PS A compressed or non-flat headphone will bring out gobs of detail from your old records due to playing the soft parts louder and enabling our hearing to hear sounds that were mostly masked on flat headphones.