A microphone is an acoustic-to-electric transducer or sensor that converts sound in air into an electrical signal.
Microphones are used in many applications such as telephones, hearing aids, public address systems, film production, radio and television broadcasting, in computers and for non-acoustic purposes such as ultrasonic checking.
Most microphones today use electromagnetic induction (dynamic microphones), capacitance change (condenser microphones) or piezoelectricity (piezoelectric microphones) to produce an electrical signal from air pressure variations.
Microphones typically need to be connected to a preamplifier before the signal can be amplified with an audio power amplifier or recorded.
This spring-suspended microphone, with its original box and instruction leaflet, was made by the company Telsen Electric Co (1935) Ltd and dates to between 1935 and 1940.
This microphone, an Ace type 68, which came with a transformer, could be used for personal and home recording.