Shotgun microphone

The term shotgun microphone (shotgun mic) for short shotgun or interference microphone designates a microphone design with a special acoustic functionality, in which the microphone body is a conceptual part of the design through a pre-built interference tube . A shotgun microphone has a distinctive lobe characteristic .

Directional characteristic lobe

functionality

A pressure gradient microphone is placed in front of an interference tube that is open to the front and provided with slots or bores on the side. This causes a clear directional effect to the front in the range of medium and high frequencies.

Interference or shotgun microphone

Sennheiser MKH 416

The microphone capsule in pressure gradient design initially has a cardioid or hypercardioid characteristic. Sound waves arriving from the 0 ° direction along the pipe's longitudinal axis add up in phase at the pipe end. Sound waves that do not hit the interference tube head-on are diffracted into the tube through the side slits . A phase shift occurs; Interference (superimposition) leads to extinction within the pipe in the case of the sound arriving from the side. Due to this functional principle, shotgun microphones are also referred to as interference microphones or interference receivers.
The lowest frequency at which this cancellation works depends on the length of the shotgun used; The bundling works roughly from the frequency whose wavelength corresponds to the shotgun length.
Calculation example: If the directional tube is to be effective from around 100 Hz, the wavelength at the speed of sound is c = 343 m / s at 20 ° C:

${\displaystyle {\frac {343\,\mathrm {m} /\mathrm {s} }{100/\mathrm {s} }}=3{,}43\,\mathrm {m} }$

So you would need a shotgun length of well over 3 m. For reasons of handiness, the effective lobe characteristic for the common shotgun lengths of 0.3 m only results above 1 kHz and increases with higher frequencies. Below 1 kHz, the directivity corresponds to that of the microphone capsule - a cardioid or hypercardioid pattern. Strictly speaking, the shotgun microphone therefore has two directional characteristics. As a pressure gradient microphone, the shotgun microphone sounds quite poor in depth. When sounding up close, it reacts with a clear increase in the bass ( close-up effect ). It is therefore occasionally used as a report microphone (handheld microphone). Conversion techniques based on the principle of the condenser or electret microphone are common .

Practical use

Shotgun microphones are particularly suitable for situations in which microphones cannot be used at close range (mostly for optical reasons):

• Support microphone from a distance on theater stages and orchestral recordings
• Invisible microphone for cinema, film and television recordings (" Tonangel ")
• Clip-on directional microphone on video and film cameras
• Telemetry measurement on fast-flying objects
• Listening microphone at sporting events, e.g. B. in American football

In addition to the word “shotgun microphone” there is the word “shotgun microphone” with the same meaning. Often offered as an accessory for camcorders and television cameras, the shotgun leads to hopes that are often not fulfilled in practice. The frequent comparison with a telephoto lens and the possibility of zooming in is incorrect because no directional microphone amplifies the sound incident on its axis. The directivity comes from the fact that the sound from other directions is suppressed. In an anechoic room you can record “distant” sound sources with a sphere just as well as with a microphone in any direction. Only by reflected ambient noise or by lateral interference sound is a benefit resulting from the use of directional microphones. Even if the diffuse room sound is much louder than the direct sound - if the microphone is outside the reverberation radius , this cancellation no longer works reliably. Therefore, the effective directivity of each directional microphone decreases when the distance to the sound source increases and the diffuse field component increases.

See also

• Recording area
• Miking
• Microphone windscreen
• Proximity effect

literature

• Michael Dickreiter , Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Manual of the recording studio technology. 8th, revised and expanded edition, 2 volumes, publisher: Walter de Gruyter, Berlin / Boston 2014, ISBN 978-3-11-028978-7 or e- ISBN 978-3-11-031650-6

Individual evidence

1. ^ Michael Dickreiter: Handbook of the recording studio technology. 6th edition 1997, Volume 1, p. 171.
2. ↑ Thomas Görne: Microphones in theory and practice. 2nd Edition. Elektor-Verlag, Aachen 1996, ISBN 3-928051-76-8 , p. 97.