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Directivity Index (DI)


Directivity Index (DI) and Polar Measures

The Directivity Index (DI) of a directional microphone array is the ratio of the microphone output for a sound source positioned directly in front of the microphone array to that array's output measured in a diffuse sound field of the same total acoustic power. A diffuse sound field is one in which the statistical distribution of sound energy is uniform throughout the sound field and the directions of wave propagation are randomly distributed. While this definition of a diffuse field DI is a theoretical ideal, a representative measure can be derived in a free-field using an anechoic chamber and single loudspeaker. The methodology for this approach is outlined below. Knowledge of a directional microphone's DI is useful in that this information may be interpreted as an estimate of the effective signal to ambient noise ratio improvement when the directional microphone is active. It is reasonable to expect that in many noisy listening situations increasing a directional microphone's DI will improve signal-to-noise ratio and result in improved speech recognition ability and comfort for the listener.


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