(left) RCA 44-BX ribbon microphone from 1940. (right) RCA Type 44 with the cover off. The magnet is visible at center, and the narrow aluminum ribbon is suspended between the triangular pole pieces (top).
A ribbon microphone, also known as a ribbon velocity microphone, is a type of microphone that uses a thin aluminum, duraluminum or nanofilm of electrically conductive ribbon placed between the poles of a magnet to produce a voltage by electromagnetic induction. Ribbon microphones are typically bidirectional, meaning that they pick up sounds equally well from either side of the microphone.