The single-button carbon microphone was widely used in the "candlestick" telephone made by Western Electric, models 299 and 323, from 1915 to the 1920s. This type of microphone was suitable for the limited voice range of telephones, but carbon produced too much noise for music recording.
Hoover with radio mics from Literary Digest 1929/05/04
The spring-mounted double-button carbon microphone was designed to keep the carbon granules inside the transmitter from moving and touching the diaphragm during operation. Western Electric introduced the first model 373W in 1920, followed by improved the improved model 387, the smaller 389 (used on top of a candlestick stand as the 1441CJ announce mic), and the model 600A.
1925 WE 1B used by Hoover from Literary Digest 1925/12/19
373-W in the WE 1B mount #25603 from AT&T Archives
The Western Electric 1A or 1B housings enclosed the same carbon transmitters used in the spring-mounted versions. The spring-mounted and enclosed versions were widely used in radio broadcasting 1921-1931.
