cockpit noise

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

"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

Put a muff over it? A muff keeps mine from triggering the voice-activation
of the ancient Softcomm intercom in a Taylorcraft, which is noise incarnate.

I recently flew a 172 which was amazingly quiet. We could talk in the
cockpit without much noise at all while the 172 cruised along at 125. Now
I can see why it was so quiet because as we took out the interior, including
the door and side panels for replacement because they looked like hell, they
were plush and foam-backed. So were the carpets. The doors were stuffed
with fiberglas insulation and so were other little nooks and crannies.

On Sat, 5 Jun 2004 18:43:46 -0400, " jls"
wrote:


"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

Put a muff over it? A muff keeps mine from triggering the voice-activation
of the ancient Softcomm intercom in a Taylorcraft, which is noise incarnate.

I recently flew a 172 which was amazingly quiet. We could talk in the
cockpit without much noise at all while the 172 cruised along at 125. Now
I can see why it was so quiet because as we took out the interior, including
the door and side panels for replacement because they looked like hell, they
were plush and foam-backed. So were the carpets. The doors were stuffed
with fiberglas insulation and so were other little nooks and crannies.


Just out of curiosity, how much did your useful load improve?
--
dillon

When I was a kid, I thought the angel's name was Hark
and the horse's name was Bob.

"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?

It's not so much the sensitivity as the noise canceling properties. Well
designed noise canceling microphones have inlets on the "lip" side of the
mike and matching inlets on the "front" side. The circuitry filters the
one-sided voice input from the "lip" side and uses that to transmit. The
noise that comes in both sides is thrown in the trash.

I'm not explaining this well, nor could I describe the circuit - but it
works. Pull the foam wind-noise muffler off your mike and see if there are
slits on both the front and back of the plastic housing. If there are, it
should be a noise canceling design. If not - look for another unit.

Rich "Talking out of one side of my mouth" S.

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

Sometimes the easiest solution to this problem is to put the mic closer to the
source of the sound that you want transmitted....i.e. your mouth. I find
frequently, that passengers are not used to having the mic that close to their
mouth...even perhaps touching their bottom lip.

Decreasing the distance to the source increases the "signal" strength. The
noise level remains constant. You have effectively increased your signal to
noise ratio.

Dave

I have a muff on the mike , if it was any closer I'd have to swallow it !
There are slits on both sides of the mike .
When using the radio the transmissions are noisy but undestandable , the
intercom is another story ,I can squelch out the noise but when speaking the
squelch opens and all you hear is engine noise ( not electrical
interference)with a voice in it . What I need to do is filter out the
background noise somehow. Any suggestions? Peter.

Get a better headset. The noise reduction in the mic of one (or more) of the
headsets plugged in is inadequate. I've used the gamut of different flavors, and many
of the well-respected brands have rather crappy noise reduction on the mics. My
cheesy $100 FlightLine 60HS-B passive headset had *great* mic noise reduction (albeit
at a lower sensitivity) than the Lightspeed 15K, 15XL, 25XL's I've used. Now I've
been using a Lightspeed QFR XC2, which seems to have noise attentuation somewhere in
the middle.

If you were to filter the noise out of the mic, you'll probably filter out the
voice signal you want too. Unless of course you do some very fancy filtering (read:
DSP)

-Cory
Peter Thornton wrote:
: I have a muff on the mike , if it was any closer I'd have to swallow it !
: There are slits on both sides of the mike .
: When using the radio the transmissions are noisy but undestandable , the
: intercom is another story ,I can squelch out the noise but when speaking the
: squelch opens and all you hear is engine noise ( not electrical
: interference)with a voice in it . What I need to do is filter out the
: background noise somehow. Any suggestions? Peter.



--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************

"Peter Thornton" wrote in message
...
I have a muff on the mike , if it was any closer I'd have to swallow it !
There are slits on both sides of the mike .
When using the radio the transmissions are noisy but undestandable , the
intercom is another story ,I can squelch out the noise but when speaking
the
squelch opens and all you hear is engine noise ( not electrical
interference)with a voice in it . What I need to do is filter out the
background noise somehow. Any suggestions? Peter.

Usually, one of the things that contributes to this is the VOX operation.
When you start to speak, ALL mikes that are plugged in open up. You could
try using a PTT arrangement which only open the mike of the person speaking.

Rich S.

That reminds me, too.... some of the fancier intercoms have multiple
squelches. Mine has multiple thresholds (independently adjustable), but when it
opens, it opens all of them. Some not only have that, but only opens the mic on the
one that broke squelch. To narrow it down, I'd still say try flying with only one
headset plugged in. If that one headset makes too much noise, a new intercom won't
help.... new headset will.

-Cory


Rich S. wrote:
: "Peter Thornton" wrote in message
: ...
: I have a muff on the mike , if it was any closer I'd have to swallow it !
: There are slits on both sides of the mike .
: When using the radio the transmissions are noisy but undestandable , the
: intercom is another story ,I can squelch out the noise but when speaking
: the
: squelch opens and all you hear is engine noise ( not electrical
: interference)with a voice in it . What I need to do is filter out the
: background noise somehow. Any suggestions? Peter.

: Usually, one of the things that contributes to this is the VOX operation.
: When you start to speak, ALL mikes that are plugged in open up. You could
: try using a PTT arrangement which only open the mike of the person speaking.

: Rich S.



--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************