Description:
<jats:p>The spatial variation of the reverberation time in the 1/3-octave bands from 80 to 10 000 Hz was studied as a function of: (1) the surface area of the absorbing material ranging from 0 to 13.4 m2; (2) the orientation and rotational speed (0–10 rpm) of the vanes; (3) loudspeaker placement and type; (4) discrete microphone versus high-speed multiplexed data acquisition; (5) the number of microphones; and (6) the number of decay times averaged at a given microphone location. For the case of the vanes rotating at 7.5 rpm it was found that the standard deviation of spatial variation of the reverberation time from 12 microphones ranged from 1% to 12% of the mean value in the frequency bands below 400 Hz, was less than 0.5% from 400 to 5000 Hz and increased to 1.5% at 10 000 Hz. The values were virtually independent of the surface area of the absorbing material placed in the room. With the vanes stationary these percentages increased by as much as a factor of 5. In addition to the decrease in the spatial variance with the vanes rotating, the spatially-averaged reverberation time decreased by 2% to 15% in the frequency bands below 500 Hz.</jats:p>