A microphone, colloquially called a mic, or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers and other electronic devices, such as mobile phones, for recording sounds, speech recognition, VoIP, and other purposes, such as ultrasonic sensors or knock sensors.
Shure Brothers microphone, model 55S, multi-impedance "Small Unidyne" dynamic from 1951
David Edward Hughes invented a carbon microphone in the 1870s.
Humphrey Bogart, Jack Brown, and Lauren Bacall with RCA Varacoustic MI-6203 ribbon microphones broadcast to troops overseas during World War II.
Inside the Oktava 319 condenser microphone
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities. The process of converting one form of energy to another is known as transduction.
Mechanical transducer