Two Western Electric double button carbon microphones from 1938. Developed by Western Electric in 1921, the double button carbon microphone was a higher fidelity version of the ordinary carbon microphone and was widely used for public address systems, recording, and radio broadcasting during the 1920s and 30s. They are now often referred to as "ring and spring" microphones due to the spring suspension system, which isolated the sensor unit acoustically from its support stand.