Peter, there is more to it than simply "...reduce the sensitivity of
the mike".
In a noisy environment, it is the "signsl-to-noise ratio" (S/N) that
suffers. The "signal" being your voice and the "noise" being just
that. One can turn down the audio gain in the radio but that lowers
both signal and noise together and generally will not help (exception
mentioned later).
Rich S. was correct about the electronic-type noise canceling mikes.
There are also accoustic-type noise canceling mikes which also have
the holes on both front and back of the mouthpiece but each set of
holes feeds a tube that goes down the boom to a single microphone
element (dynamic), the two tubes driving opposite sides of the
element. The Military uses (used?) this type and altho somewhat
"tinny" sounding they are quite effective.

Exception regerding "turning down the gain": If by chance the audio
gain (mic gain) of the transmitter is set way too high, even a good
S/N mike will fail to yield good sounding audio because with the gain
too high the audio circuit overloads (limits) on the voice
(signal)allowing the noise to effectively rise to equal level.
Turning down the gain is an easy try and you may luck-out but it
probably won't be that easy.

Sid Knox
Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ


"Peter Thornton" wrote in message ...
I have the unusual need to decrease the sensitivity of my headset mike. The
aircraft I fly has a very noisy cockpit (tube and fabric two stroke pusher )
when I transmit the mike picks up alot of background noise. The headset is
an avcom ac900 flex boom ,mike is an M71 I tried a mike from a DC headset it
was better but still not great. Is there anything I can do to reduce the
sensitivity of the mike?

Thanks in advance , Peter T