No, no problem - I've just got a decent collection of headphones, aiming for variety, and have noticed that my experiences with them seem to match the phenomenological/qualitative reports of others when it comes to "fast or slow" especially... And further that there seems to be something related to driver speed that may show up as a given sort of treble profile on a frequency response graph. See Grado graphs, Beyer graphs, Sennheiser graphs... But it's a weak hypothesis at the moment because there's just not a lot of data to go on at the moment, the plural of anecdote is not data
I don't have the requisite free cash to buy every headphone I'd want to test, but if I had access to Headroom's testing setup I'd work out an experimental design which in order measured driver mass and impedance, then frequency response, then impulse response, then square response at 40 and an octave above, then waterfall plots of short pink noise pulses.
To put it straightforwardly, headphones with spikey looking treble seem to be fast, while headphones with dipped treble seem to be slow. I would like to know more about why that is. Two that interest me in particular are the AKG K701/702/Q701 and the HD-650, because they use really similar driver technology and despite substantially varying impedance (1khz, average and peak) require more or less the same power to be driven appropriately, but they don't behave very similarly in many aspects. Sennheiser's Duofoil and AKG's Varimotion both use a thicker center mass to act as a sort of tweeter for nearly-discrete high frequency reproduction, and thinner diaphragms around the center for reproduction of the sub-bass, bass, midbass, midrange and low treble frequency reproduction. They have their own names for it of course, haha, but nonetheless what it is doesn't differ dramatically. Many other factors go into the
overall sound reproduction, of course, and it would be really foolish to ignore all that, but there's something about the drivers specifically which interests me and I would like to be able to explore it in more depth. So while the 10khz-20khz octave doesn't hold a tremendous amount of information per se, it's one of the few hopefully comparable data points that might offer some evidence that could eventually lead to a better answer for my question, which doesn't intercede between me and my enjoyment of headphones at all but which sure does make me curious as to what could be the cause of what I and others hear.
I'm not the original poster of this thread, the OP's question isn't mine, just somewhat related since it made me think of how much more useful it would be for me to have a linear graph of the interesting high frequency profiles of various cans without having to figure out a way to test them myself in person. Hope that explains it. May not be anything that interests anyone else in the least, just a pet curiosity of mine.