Yup. Electrostats seem to fall in the infinite baffle category as well.
Leaky pads may offer a porous coupling that I think acts like an anechoic chamber. However, while leaky coupling materials like foam (of several densities) or sponge may offer some acoustic impedance, it is not perfect as some air escapes through them. It may be possible to circumvent this by using a solid plate with an irregular (perhaps sponge like) material in the inside. But there might be more to it since using this still may result in too much gain in the low frequencies (using ones own senses as a reference).
I think there is indeed the possibility that the coupling type (leaky vs sealed) alters the radiation pattern depending on driver size and configuration. The alteration of the radiation pattern may not be uniform across frequency. This may indeed be a function of the can type: dipole vs infinite baffle.
Good to see some attempts at understanding the whole picture (in the field of padology..).
Worth remembering that the hole in the scull ( the actual ear opening) is small, and surrounded by a rather flat bone surface. This means that -in particular -in the case of electro- or magnetostats the ear is trapped between two parallel surfaces, with all the implications (despite the dampening effect of more or less succulent ears, various amounts of subcutaneous fat etc, differing considerable from person to person and btw probably giving much more FR variation than different pad materials).
In any case the standing waves between these surfaces, means that the distance between them will affect the FR to a certain degree in the high treble area. (Say, in some cases softer pads may simply reduce the distance in question).
In general, in the case of “tea cup” standing waves, some potential nasty peak could possibly be reduced by moving the drivers sideways relative to the ear, why some kind of eccentric pads might be of use. Rectangular, oval or irregular shapes would also be of potential benefit. (I have never drunk tea from rectangular cups, otoh)..
The Oppo measurements by Tyll showed a surprising regularity in the upper half of the chart. I think that by measuring the pads, it should be possible to isolate the -supposedly single! - determining acoustic factor in this case. (In the lower half of the chart everything seems to be about more or less seal, I suppose).
"... by using a solid plate with an irregular (perhaps sponge like) material in the inside. But there might be more to it since using this still may result in too much gain in the low frequencies"
One needs not fear too much bass in this case IMO, since modifying/tuning the plate by perforations or smth would always be a possibility. ( this reminds me somewhat about my recent post about futuristic 3D printed pads, individually fitted).
Olaf
