Edited by Cristello - 9/5/13 at 9:18am
For the sake of clarity, would you be able to verify that it was only the driver being measured (and not other possible sources of resonances)? Also, I assume that the driver was measured "free-field". Is this correct?
I am testing a theory based on your data and some of my own, but am waiting to post any results until I can confirm their relevance.
I've not measured the driver out of its cup, if that's what you meant. I've measured the K 250 with and without a seal (the latter was a microphone capsule hanging freely in the air over the baffle) and gotten the same ringing in the measurements. I also got similar ringing from measuring the K 241, which is possibly the same driver but in a different cup. That specific measurement you quoted was with a seal.
I made a post there -> http://www.head-fi.org/t/566929/headphone-csd-waterfall-plots/855#post_8788251 specifically about smoothing out ringing on the K 250. For whatever reason, that convolution filter got rid of the ridges even though the other one didn't. (But the basic problem remains with that filter as well: it's tied to the frequency response you feed it, and without knowing the response at your own eardrum, its applicability is limited. Works nice for the measurement ear, though.)
xnor used convolution, did he not?
The transients produced by the driver are as fast as the test signal asks them to be; how much more can be asked for? The raggedness in the c graph I would attribute partly to poor SNR given that it was recorded at low volume. Aligning a and c on top of each other shows that the transients are perfect up and down. I dare you to find an electrostat that can do the same without the input being altered (I also dare you to show rather than just tell). Do this for me and I'll convolve a pair of phones that perform really badly stock.
EQ processes the signal before output, physical modding processes it either during or after output. All before it reaches the ear. If the resulting waves at the eardrum are the same, what is the difference?
I think my HE400s (planar) are fast, and when I say that I mean the drivers respond quickly and are well controlled. I think this is because the drivers/diaphragms are very light and easy to move and the magnetic field is very strong. In dynamic headphones the driver is heavier and more difficult to control.
Does that make sense?
Hopefully this is helpful...