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Re: contact microphones - how?

eileen wants to contact live objects like a cat:
>>  I wonder if you could adapt a mic with a stethoscope for internal body
>>  sounds.
>I've actually thought of that. I was thinking how I could channel the 
>to something I could record, not to lose any of the sensitivity a
>stethoscope can offer.

the stethoscope just transfers the sound through a tube. Too much 
loss, and the mic can as well be at the source.

>Here's a great link I found on "how to" build a contact mic. I'm using it
>with a mini-disc recorder, so I had to change the 1/4" phone jack to a 
>stereo phone plug. Hopefully it will work when I put it all together.
>Someone else also suggested that I try something similar (with not as much
>work). Cut an RCA cable in half and strip the inside wires (2). Then 
>the wires to the Piezo disc (or attach the 2 wires already connected to 
>Piezo disc). From there it's a simple RCA to stereo 1/4" (or 1/8") adapter
>away from connecting into any sort of recording device. I haven't tried 
>option yet but sounds like it could work.

sounds like the same, since in that link, they just operate a Piezo 
disc out of a plastic box. And they are available without box, very 
cheaply, dont ask me where.
Dont forget that the piezo needs a high impedance input (at least 
like an electic guitar). If you drive it directly to the mixer, you 
loose all bass. Just put some stomp box in between, they usually 
convert the impedance even if they are switched off.

I am really used to drill a whole into the thing I want to capture ;-(
Then again, I have seen contact mics in the army for use in noisy 
ambients: Its a little black box you attach to the throat. 
Interesting sound. I guess there is a piezo in it. So it should work 
on the cats throat, too.
The point about piezo pickups is that they dont translate movement 
(since they are very stiff) but pressure. Either bending or pressing.
So the best way is to mount it where the pressure is biggest. Between 
string and bridge, or between the vocal chord and the bones that hold 
The less effective way is to attach it to the vibrating object (sound 
board, throat) and have a weight on the other side of the piezo which 
turns this movement into a force by inertia. I guess thats why the 
army throat mic was not very small (exept that they liked heavy stuff 
anyway when I knew the army, 20 years ago ;-). You see similar 
weights on contact mics attached to guitar tops. If its too light, 
you get no bass. If its too heavy, the guitar will sound less and the 
cat will not purr...
Also, the contact to the object should be pretty direct. So it may 
take some shaving of the cats throat ;-(
I would probably try a small dynamic mic (movement sensitive) 
attached to the throat first.

Have fun and tell us how it sounds or better put up some mp3...

You are free to send this text to the guy with the page about contact 
mics... ;-)

          ---> http://Matthias.Grob.org