07/12/2019
Another unique transducer is the Geophone. Geophones were originally designed to detect earthquakes, but they are also used to explore for oil and gas, where they are deployed in large arrays to pick up the signals over an area that is excited by "thumpers" or explosive charges.
Geophones are constructed by suspending a coil of wire on springs around a strong magnet. any vibration in the vertical plane causes the coil of wire to move up and down, thus creating a varying current (A.C.) in the coil. This current can be amplified to produce sound that is the result of that vibration.
As a result, Geophones are very sensitive pickups for vibration and can be thought of as a "poor person's accelerometer" when used for sound-vibration pickup. They do not need special preamps or power to operate, just the normal mic input on a field recorder (or mixer board). In fact, they work especially well into balanced mic preamps with XLR connectors due to their low impedance. No phantom power is required.
Geophones do not have a very high frequency response since they are electromechanical transducers, but their tone is mellow and they respond to vibrations of only a few Hz. Good for a great many purposes.