The Velocity (Ribbon) Microphone

Author: N.H. Crowhurst

Another microphone that uses the same basic idea is the ribbon type. Instead of having a coil of wire, however, a single flat flexible ribbon of aluminum, or aluminum alloy, is used. It moves with the air vibrations, and the magnet poles on either side of it cause it to generate currents. The two basic microphone actions are thus served by the ribbon alone - it acts as both diaphragm and transducer.

Basic construction of a ribbon microphone.

The ribbon microphone is also called the velocity type, because its response is proportional to the velocity of motion of the air particles in the sound wave rather than to pressure fluctuations. These microphones are also called pressure-gradient microphones because the movement of the ribbon is due to the pressure gradient - the difference in a pressure caused by the sound wave - between its back and its front. It is this constantly changing difference in pressure, of course, that controls the velocity at which the air particles move around the ribbon. Hence both "velocity" and "pressure gradient" are equally descriptive of the action of the ribbon microphone.