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7 - DIAPHRAGM MOVEMENT AND SIGNAL GENERATION

The process of signal generation in a microphone is dependent upon the sound wave setting up mechanical vibrations of the microphone diaphragm. The voltage generated by the vibration of this moving element may be proportional either to the velocity or to the amplitude of this oscillatory movement.

Constant velocity - If the sound intensity is constant and independent of frequency, then the velocity of the moving element must be constant over the whole of the audible frequency range in order to generate a constant electrical output. Electrodynamic moving coil and ribbon microphones are examples of this constant-velocity vibration. The amplitude of vibration of the moving element of an electrodynamic moving coil or ribbon microphone is inversely proportional to the frequency.

Constant amplitude – In this case, if the sound intensity is constant and independent of frequency, then the amplitude of displacement of the moving element must be constant throughout the whole of the audible frequency range in order to generate a constant electrical output. The electrostatic or condenser microphone is an example of this constant-amplitude vibration. On the other hand the velocity of vibration of the moving element of an electrostatic microphone is proportional to frequency.

Constant velocity/constant voltage signal generation is one aspect of the classification of microphones which is certainly of importance as a design consideration, but does not have a direct impact on the operational use of the microphone.