Effects of absorption placement on interior noise levels—A theoretical study

Abstract

The effect of the spatial distribution of absorbing surfaces on the sound field in enclosures is investigated. For a given overall level of absorption, the difference between distributing the absorption uniformly or localizing it in a single region is studied. Attention is focused on the high-frequency range having wavelengths small compared to the enclosure dimensions, but either large or small compared to the absorptive region. The distribution of mean-square pressure in a bandwidth is studied to ascertain the degree of uniformity throughout the enclosure, and particularly in the vicinity of the absorbing region. Of special interest is the effect of absorption on intensification zones, which are the regions near boundaries where there is a high degree of spatial correlation between modes. Depending upon the amount of absorption, the center frequency wavelength and/or the dimensions of the absorber are used to determine the size of nonuniform regions in the enclosure. The study is conducted using classical modal analysis. The results provide physical insight into the behavior of acoustic fields in enclosures.