Thursday, 24 May 2012

I grew a microphone

So the image above is one of a few hundred crystals I grew from readily available kitchen ingredients in my kitchen the other night. It is a crystal of 'Rochelle' salt and is made by doing a bit of home chemistry with some cream of tartar and some sodium bicarbonate (both of these are available from any shop that sells baking stuff). The interesting thing about these crystals is that they are piezoelectric in nature meaning that if the are made to vibrate the produce a voltage. This is the exact principle in play with contact microphones and so with a bit of fiddling to clamp the crystal between 2 conductive plates (bits of tinfoil folded round a bare wire!) these crystals can be used to make this

I originally got the idea when I saw this video on Collin's lab ages ago.....

......but in the video Collin uses cream of tartare and sodium carbonate which I could not find...I wondered though if he could have made a microphone out of his crystals that he grew.....however like many thoughts I filed it away and promptly forgot about it. That was until I saw this post from the mighty Leafcutter John (I was perusing his site looking at his hydrophones...another thought on the great todo pile). In this post Leafcutter John provides the answer that if you bake sodium bicarbonate for an hour at 150C it turns into sodium carbonate...and he had indeed managed to get his crystals working as a contact mic.

So the other night I turned my kitchen into what I imagine a meth lab looks like and managed to grow some crystals and make the contact mic as seen above, now they are pretty low output and the mic preamp on my tinkering/hacking mixer didn't lift it much and I needed to attach the mic to a battery powered amp and then record the output. I attached this to my diy street sweeper bristle kalimba and had a plink around and here is the result with no effects but a bit of the top end hiss rolled off!

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