Directivity

The pattern of sensitivity of a microphone according to direction, usually demonstrated as a polar diagram where the length of the radius in any direction gives the response in decibels of the microphone.

Usually this response is measured for various frequencies, the results of which may be combined in a single diagram, since in many cases a uniformity of response over a large frequency range is desirable. The directional characteristics of the acoustic radiation of any sound source including loudspeakers may also be indicated by such diagrams.

Directivity patterns of various microphone types. Note the frequency dependence of the omni-directional microphone pattern.

Directivity is also called field pattem, polar pattern, or directional characteristic, and the major types for microphones are:

• cardioid or uni-directional: having greatest sensitivity at the front, only partially at the sides, and little at the back;
• bi-directional or figure-of-eight: having greatest sensitivity at front and back, but little at the sides, usually used for interviews;
• omni-directional: sensitivity about equal in all directions;
• shotgun: highly focused or 'pointed' sensitivity in one direction only.

For a discussion of the Blumlein microphone technique, see stereophonic. Compare: Minimum Audible Angle, Parabolic Reflector.