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I may be mistaken but I think the piezoelectric effect produces a charge, not a voltage, to be precise. They have ideally infinite DC impedance, like a capacitor. True charge amps are hard to build but are used, instead of voltage preamps, for piezoelectric accelerometers in the acoustics and vibration instrumentation. But I've had fine results just plugging a bare disc into a guitar amp, and sticking the disc between bridge and body as Matthias suggests. Another conceptually interesting feature of piezo material is its symmetry-- if you apply an external charge to the material, it moves! (a very tiny bit). In my copious spare time I hope to develop an e-bow/Sustainiac like device that would work on non-metallic objects, using this principle. (Don't hold your breath.) Most piezoelectric material is also pyroelectric, meaning it generates an electrical response to heat. Perhaps some of the recent threads on "hot" looping can take note of this to good effect. :-) Does anyone really know how C-ducers work? I believe they are capacitive, because the foil inside the pickup thingy is not Kynar (a piezoelectric mylar) or anything like it. In fact I have made pickups with aluminum foil and scotch tape, which work amazingly well into a C-ducer preamp but don't make a peep plugged into anything else. Here's a link to some cool piezo sensor products: http://www.msiusa.com/piezo I bought this company's design kit from Digikey. They now have online ordering from their site, and I notice there are now some $25 hydrophone products listed too. The piezo cable looks really interesting. Bernie Krause recommended to me hydrophones from Underwater Acoustics in Vancouver BC. Barbara there was very helpful and sold me one of the very nice units they use for eco-tourist whale listening. Bernie also echoed the comments of many film sound designers, that a real world recording rarely sounds like we imagine it, especially with something so subtle as water. You often need to create the desired "nature" sound with multiple tracks and more in the studio. I couldn't find a URL for that company, but have the info somewhere on paper if anyone's interested. I did just find a link to another very nice looking professional hydrophone product: http://www.dolphinear.com/pro/index.htm If anyone has the $300 to blow on one of these, let us all know how well it works!!! My all time favorite underwater recordings use the tried-and-true but rather risky Neumann-with-a-condom technique. The serpent fight scene in the live action Jungle Book movie features sounds I recorded in this manner in a hot tub with my wife. I should loop those tracks and call it Freudian Field Day... -Alex S. At 4:57 PM -0300 10/3/02, Matthias Grob wrote: >>The piezo mic is two thin layers of metal, with a layer >>of ceramic between. Typically 1 to 2 centimeters in diameter, >>and less than a millimeter thick. When the element flexes, >>a tiny amount of electricity is generated. > >they react on pressure in the first place. In a lighter, you press >on them and the resulting voltage is so hight that a spark results. > >>A pre-amp is >>needed. > >the impedance depends on size. Its always bigger for low >frequencies, so a small element for full range needs about 2Megohm >input impedance. If you have a big element and/or dont need the low >frequencies, it can be much lower. > >>As far as I know, they work best on large, flat surfaces >>that resonate with the sound. > >between an activator and the base they work even better. > >>The prime example is the front of an accoustic guitar. > >better example is the bridge, between string and body. You can get >several volts there. > >>A flute probably won't work. > >yes, air movement is not enough, it takes a vibrating hard material. >The tube of a flute vibrates but maybe not enough. > >> >>However, what is so cool about them is that they are cheap >>if you make your own, which is pretty easy. Buy the bare >>element, or disassemble a Radio Shack buzzer, attach the >>wires, and you've only spent a couple bucks. Stick it to your >>instrument and see what happens. Try different spots, and >>wire two together for fun. I plan to embed a couple >>inside a hollow body kalimba I'm building. >> >> >>I originally found via Google some long posts from an >>guitar discussion group on the topic, but much instruction >>isn't needed because it is so easy. >> >>Yours in rhythm, >>Steve > > >-- > > > ---> http://Matthias.Grob.org