Audio transducers

A transducer is a device that turns one type of energy into another. A light bulb turns electrical current into light. A photodiode turns a varying amount of light into varying current. A radio transmitter antenna converts electrical currents into radio waves. A radio receiver antenna converts radio waves into electrical currents. These are types of transducers.

The term "transducer" most-commonly means a microphone and a bit less-commonly a loudspeaker.