Free field equalization

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The free field equalization is a linearization of the frequency response of a pressure microphone that is located in the free sound field , which is also called the direct sound field D. In the free field , the sound hits the membrane from one direction, the main direction 0 °, at a right angle , in contrast to the diffuse field , which is also called the room sound field R, in which the sound hits the membrane evenly from all directions.
By interference of the reflected sound components with the directly arriving at the immission shares a sound pressure level change by up to 6 dB for frequency components whose wavelength is less than or equal to the diaphragm diameter is obtained in the main direction of 0 °. This is the so-called pressure jam . With pressure gradient microphones , there can be no free- field equalization or diffuse-field equalization .

With a free-field equalized microphone, this height increase is compensated for the main direction of incidence 0 °. In the free field, i.e. when there are no reflections, there is therefore a linear frequency response. In the diffuse field , the free-field equalized microphone exhibits overall height attenuation.

Analogous to this, there are also microphones that are equalized for the diffuse field, in which sound components come in evenly from all directions. In the case of diffuse field equalized microphones, a linear frequency response results in the diffuse field; in the free field, diffuse field equalized microphones show the treble increase described above.

The free field equalization and the diffuse field equalization are also used with artificial heads , loudspeakers and headphones .

literature

  • Thomas Görne: Sound engineering. 1st edition, Carl Hanser Verlag, Leipzig, 2006, ISBN 3-446-40198-9
  • Michael Dickreiter: "Microphone recording technology" 3rd edition, Hirzel Verlag, 2003, ISBN 3-7776-1199-9

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