Magnus,
I forgot to discuss the audiograms. Mic noise is more audible in the
Kilohertz range, so you can ignore the house or other noises below 1KHz.
To get a cleaner noise graph, cover the mics with a pile of bedclothes whic=
h
will absorb the higher frequencies. The "thermal noise" of the vibrating ai=
r
molecules is the lowest noise you can get, and "excess noise" is the total=
air plus mic noise above that fundamental level. The theoretical minimum
"excess noise" would be 3dB as the air is vibrating on both sides of the mi=
c
diaphragm.
I have seen noise specs which were taken with the capsule disconnected.
These figures are meaningless.
Thermal noise rises with frequency, and sometimes shows up by rising on an=
audiogram above around 7KHz. This may be thermal noise in the mic, but an H=
F
tip-up means that you are at a low fundamental noise limit. The VP88 graph=
may show the start of thermal noise above 12KHz, which is promising.
David Brinicombe
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