Studies on the spatial variation of decaying sound fields
Thomas W. Bartel, Edward B. Magrab · The Journal of the Acoustical Society of America · 1978
The spatial variation of the reverberation time was measured in the NBS reverberation room in the 1/3-octave bands from 80 to 10 000 Hz to determine the following: (1) the effects on the precision of the spatially averaged reverberation time due to (i) vane speed and vane orientation, (ii) loudspeaker location, and (iii) the area and location of an absorbing panel and its absorption coefficient; (2) the selection of the parameters in (1) above such that the measurement uncertainty of the reverberation time is minimized; and (3) the overall measurement uncertainty for this optimum configuration as a function of the number of microphone locations and the number of decay curves recorded at each microphone location. For an 11-m2 panel with relatively little low frequency absorption and with the vanes oriented at 22.5° from the vertical and rotating at 7.5 rpm, an analysis of variance indicated that the total uncertainty of the measured average reverberation time (one standard deviation from the mean) was less than 0.5% from 160 to 4000 Hz and less than 1.5% from 80 to 10 000 Hz when 20 decays at each of six microphone locations were used.