The Use of Stationary Near-Field Diffusers for Improving Low-Frequency Measurements in a Reverberant Room

Abstract

For a monopole source, the interior reverberant mean-squared pressure is within ±1 dB of the asymptotic value if the source distance is greater than 0.5λ from a wall. For a spherical random dipole source, such as the Ilg reference sound source (RSS) used in the substitution technique of measuring sound power, this distance increases to about 1.0λ. Since most reverberant room dimensions are of the order of 2λ in the lowest 13-oct band of interest, some care must be exercised in low-frequency measurements. The mean-squared pressure was experimentally measured as a function of the location of the RSS in a 300-m3 a reverberant room. The results suggest that the first reflection from the walls dominates the pattern It is experimentally shown that stationary nearfield diffusers placed at the walls can be used to decrease the variance of the sound power output arising from the location of the RSS. The use of tilted walls in the design of a reverberant room should have the same effect.