About the Amazon GR02, here's the link:
Was available yesterday with 3 left. Must've been bought out, it's hot goods.
Lendmeurears is probably the closest to what I'd call "authorized seller" of VSonic IEMs on ebay.
The most natural response could be a bit V-shaped when measured on an uncompensated measurement head. The manufacturer should aim either for free field (open air) or diffuse field (room) response. Some more info: http://www.head-acoustics.de/downloads/eng/application_notes/Equalization_brochure.pdf
This doesn't contain "perceived bass" compensation, which typically should be ~6 dB/octave with 0 dB at 100 Hz, regardless of the mode of equalization - typically heard in low bass notes, slap bass and kick drums, but can be there in organ music and synthetic bass. It's even hard to measure those ranges. I'd say <= 35 Hz for the knee frequency of the rolloff is acceptable, anything other than this will have noticeably rolled off bass in some pieces..
It's easier to make a diffuse field sounding IEM, just because most IEMs have limitations at both ends of the spectrum... unless you count (properly designed) DDMs and multiple BA.
Single driver designs attempting free field sound tend to lack the bass and are somewhat rolled off in the highest end regardless. (Examples: ER-4S, RE272, CK10.)
Even diffuse field attempts tend to have some highest end rolloff or annoying resonances. The true art involves placing these likely inevitable resonances so that the user is not annoyed and the sound isn't too unnatural.
Edited by AstralStorm - 7/9/12 at 12:25am