BIDIRECTIONAL SENSITIVITY PATTERNS
A bidirectional microphone is a noise-cancelling microphone
(such as the Sennheiser HD 414 close-talking microphone that is
so popular in speech research).
A bidirectional microphone uses properties of a gradient microphone
to achieve noise cancellation. Sound pressure never arrives at the front
and the back of the microphone at the same time. However, noise, which
arrives from the side, does, and hence is cancelled.
These microphones have
directional sensitivity patterns:
Such microphones are very sensitive to placement, and cannot
be used interchangeably with recognition systems (microphone independence?).