An omnidirectional sound source is commonly used in room acoustical measurements. The omnidirectional directivity is usually approached by placing 12 loudspeakers in a regular 12-face polyhedron, called a dodecahedron. In the ISO 3382-1 standard on the measurement of room acoustical parameters, limits are imposed on the maximum allowable deviation from omnidirectional directivity of the sound source. If this deviation approaches the limits, it is recommended to take a rotational average over at least three positions around the source. The average over three equal-angular positions in the horizontal plane of a dodecahedron sound source proves to be unreliable due to the particular geometry of the dodecahedron. In this research, the impact of the stepwise rotation method on the measured directivity deviation of a dodecahedron sound source is investigated. This is done by determining the maximum directivity deviation from rotation measurements over a whole number of equal-angular steps varying from 1 to 8. The measurements have been performed in a concert hall at 1, 5 and 18 meters distance using a standard dodecahedron loudspeaker, a turntable and stationary pseudorandom white noise. It was found that the maximum directivity deviation from average within the critical distance of a dodecahedron sound source is ± 2 dB, when determined from 3 equal-angular positions. Only when using 5, 7 or 8 equal-angular positions, the maximum directivity deviation is reduced to ± 0.5 dB at all distances.
|Title of host publication||Proceedings of Forum Acusticum, Aalborg, 27 June-1 July 2011|
|Publication status||Published - 2011|
|Event||6th Forum Acusticum 2011 (FA 2011), 27 June - 01 July 2011, Aalborg, Denmark - Aalborg, Denmark|
Duration: 27 Jun 2011 → 1 Jul 2011
|Conference||6th Forum Acusticum 2011 (FA 2011), 27 June - 01 July 2011, Aalborg, Denmark|
|Period||27/06/11 → 1/07/11|