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directional microphone

A directional microphone is a microphone with a highly pronounced directional characteristic characterized by a narrow lobe pattern with a high degree of focusing. Sound that strikes the directional microphone perpendicularly is not attenuated, whereas sound arriving from the side is strongly attenuated. Directional microphones are based on interference. These are trains of vibrations that interact with each other and can cancel each other out. The directional microphone makes use of this principle, which is why it is also called an interference receiver.

In terms of construction, a directional microphone is an interference tube at one end of which the sound enters and at the other end of which the microphone capsule is located. The sound passes through the shotgun and hits the diaphragm of the microphone capsule. Since certain frequencies are affected in the tube, it is provided with opening slots on one side. This improves the sound image; at the same time, however, lateral sound enters the shotgun through the slots. This sound is reflected by the walls of the tube and forms interference with other sound that has entered through other slits, causing the sound signals that have entered from the side to be cancelled out.

Structure of a directional microphone with interference tube

Structure of a directional microphone with interference tube

The tube length corresponds to the wavelength of the lower cutoff frequency. At 1 kHz, the tube length would be 34 cm. The shorter the tube length, the higher the lower cutoff frequency.

There is a second principle for directional microphones: the parabolic microphone. It works with a parabolic mirror, which reflects the sound onto a pressure receiver at the focal point of the parabolic mirror. The directional effect of the parabolic microphone, which is used for recording bird calls, for example, only sets in above a certain frequency.

Directional microphone, Photo: Weidlinger, Austria

Directional microphone, Photo: Weidlinger, Austria

Directional microphones have the disadvantage that they have a high proximity effect, which occurs when the sound source is very close in front of the microphone. With this effect, low frequencies are emphasized more.

Informations:
Englisch: directional microphone
Updated at: 03.02.2014
#Words: 333
Links: microphone (Mic), focusing, sound, interference (I), receiver
Translations: DE
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