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Piezo-electric microphones

You will hardly ever see a piezo-electric microphone these days. But if you look under the bridge of an electro-acoustic (acoustic-electric) guitar...


The piezoelectric effect is where certain crystalline and ceramic materials have the property of generating an electric current when pressure or a bending force is applied.

This makes them sensitive to acoustic vibrations and they can produce a voltage in response to sound.

Piezo mics (or transducers as they may be called - a transducer is any device that converts one form of energy to another) are high impedance.

This means that they can produce voltage but very little current. To compensate for this, a preamplifier has to be placed very close to the transducer.

This will usually be inside the body of the electro-acoustic guitar.

The preamp will run for ages on a 9 volt alkaline battery, but it is worth remembering that if an electro-acoustic guitar, or other instrument with a piezo transducer, sounds distorted, it is almost certainly the battery that needs replacing, perhaps after a year or more of service.

By David Mellor Thursday May 1, 2003
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