A random incidence microphone is designed essentially to measure sound pressure levels in a diffuse sound field as they existed before the microphone was introduced into the diffuse sound field. At higher frequencies, the presence of the microphone in the sound field becomes more significant and will influence the measured sound pressure levels.

In general, the sound pressure around the microphone cartridge will increase because of reflections and diffraction. This pressure increase varies with different incidence directions. A random-incidence microphone is designed so that it's frequency response characteristics compensate for this pressure increase, assuming that the sound waves arrive at random from all directions.