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Old 28th April 2020
  #4
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It is often said that an object needs to be about ½ wavelength in size to reflect. This is obviously not a hard limit, but a gradually increasing thing. At 1 kHz, a surface larger than about 0,17 meters (1/2 wavelength) will start to noticeably reflect. An 0,34 m surface (1 lambda) will definitely reflect.

If the path length difference between direct sound and reflection is ½ lambda (or n + ½ lambda multiple); destructive interference will occur and you´ll experience a dip.

If reflection and direct sound are in phase (one or more whole wavelengths difference in path length); there will be constructive interference and you’ll get a boost (close to 6 dB assuming perfect reflection and minimal difference in travel length between direct and reflection (often the case if desk reflection).