Omnidirectional microphone

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A spherical surface microphone , KFM , provides a type of separator stereophony in which the sound recording is roughly imitated by the human ear.

It was developed into a product by the microphone manufacturer Schoeps following a proposal by Günther Theile (IRT Munich) in a lecture at the Tonmeistertagung 1994 . It generates spectral differences , which are frequency-dependent level differences that are undesirable in loudspeaker stereophony .

construction

The KFM 6 consists of a reflective gray plastic sphere with a diameter of 20 cm, with two microphones with omnidirectional characteristics, the membranes of which are flush with the surface of the sphere, mounted 180 ° opposite one another. The recording area is about 90 °.
The KFM 360 consists of a similar sphere with a diameter of 18 cm. The recording area is about 120 °.

conditions

Attempts were made to meet the following requirements with this stereo sound recording process:

  1. The transit time difference and the frequency-dependent level difference are roughly similar to natural hearing.
  2. The frequency response is linear for direct sound from the front.
  3. The frequency response of the diffuse room sound should also be linear.
  4. Even the flush installation of both microphones can not prevent sound colouration due to comb filter effects between the two microphones, as diploma theses show.

Microphone placement

When setting up the microphone, particular attention should be paid to the following:

  1. The relatively large amount of reverberation recorded requires an acoustically good recording room.
  2. The frequency response of the diffuse sound can only be color-free if there is an increase in high frequencies in the case of direct sound from the side , because the shadowing at high frequencies is more noticeable in the microphone facing away from the sound.
  3. If the microphone distance is too small, laterally incident sound sources lead to an increased presence with unnatural sound sharpness.
  4. The dimensions of the sphere with a diameter of 20 cm (18 cm) give the system an area of ​​around 90 ° (120 °).

The step up to the spherical surface microphone in approaching the human ear is the artificial head , the HRTF signals of which are only intended for headphone playback .

literature

  • Thomas Görne: Microphones in theory and practice. 8th edition. Elektor-Verlag, Aachen 2007, ISBN 978-3-89576-189-8 .

See also

Jecklin disk | binaural sound recording | Equivalence stereophony | Ear gap | Separator |

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