thanks for the replies,
i'm thinking of putting two capsules standing as close as possible in front of a speaker and pass some white noise throught them and monitor with a spectrum analyzer + listenning tests. i guess this should do ?
for now i tested my prototypes using an HDR7506 headphone set and a cheap mixer. One of the capsules was about 3dB less sensitive than the other, i then swapped the capsules around with their respective preamps and still got 3dB less on that same capsule... So its the capsule.
i will have to buy more of them as i only bought 4 and one was destroyed by doing some mounting tests for my microphone body prototype, two have the linkwitz mod (the ones with the 3dB difference) and one was kept original so i could make comparison tests against the linkwitz modified ones. so now i'm stock and have to buy more capsules to make an acceptable pair. though i am quite tempted to make the linkwitz mod to my last original WM61A and see if i can better match the gain with one of the already modded capsules...
also, i have a pair of (exellent) Avenson Audio ST02 i did some comparison tests against, i was not surprised to find out that it sounded quite different from the mics i've built (with and without the Linkwitz mod), the ST02 seems to lack bottom end
when compared to my prototypes (or my microphones are generous with low frequencies either way) also the ST02 have a tiny bit less gain but by ear the noise/hiss seems to be about the same.
i have no idea what capsules the ST02 use but i'm quite familiar with these mics as i've used them a lot (and i like them a lot) and by experience i almost always use a high pass filter when i use them (close or room mic) so i'm very curious to test my mics in real recording conditions and see what's going on with the very generous low end it seems ?
BTW, the circuit i'm using is the "standard" phantom powered design with the 2N5087s transistors found on the net.
i will post some photos of my proto soon
i would like to thank Stefan from http://www.homemademicrophones.com/ for maximum inspiration, Tape op who also inspired me with their omni mic project , and of course the great Lab members that take the time to answer my (apparently good) question ;-)
thanks
J