Alternatives to Three Designs for Broadband Sound Absorption

Three designs for broadband sound absorption by thin hard-backed layers, respectively, combine synthetic porous materials and resonant cavities, embed opposed arrays of horizontal plates in a porous layer and mount multiple parallel microperforated plates in a conical shell. The measured and predicted normal-incidence absorption spectra from these designs are compared with predictions for hard-backed porous layers of the same thickness that either have a small number of embedded vertical and horizontal solid partitions or consist of materials derived from natural sources. The comparisons suggest that broadband sound absorption spectra comparable with those of the more complicated designs can be obtained in ways that are simpler and potentially more sustainable for manufacturing and disposal.