Page "Acoustics" Paragraph 23

The transducers in most common loudspeakers ( e. g. woofers and tweeters ), are electromagnetic devices that generate waves using a suspended diaphragm driven by an electromagnetic voice coil, sending off pressure waves.

Electret microphones and condenser microphones employ electrostatics — as the sound wave strikes the microphone's diaphragm, it moves and induces a voltage change.

The ultrasonic systems used in medical ultrasonography employ piezoelectric transducers.

These are made from special ceramics in which mechanical vibrations and electrical fields are interlinked through a property of the material itself.