A microperforated panel (MPP) absorber is known to be one of the most promising alternatives of the next-generation sound absorbers. However, its absorption frequency range is limited to around two octaves because its absorption solely depends on the Helmholtz resonance mechanism. Therefore, the authors have proposed a combination of two different MPP absorbers in parallel, and revealed its potential for achieving a broader absorption frequency range in terms of excess attenuation. In this study, by the hybrid method of BEM and a mode expansion method, the authors investigate the relationship between the excess attenuation caused by the impedance discontinuity at the boundary of the two different MPPs and the sound absorption coefficient derived using the electro acoustical equivalent circuit model. Measurements of the normal incidence absorption coefficients are carried out to validate the equivalent circuit model, and in the experiments, the configuration of the cavity to realize the parallel arrangements for achieving wideband sound absorption is also discussed referring to the experimental results.
This paper examines the sound insulation of a single-leaf wall driven by a spherical wave. The transmitted sound field of an infinite elastic plate under a spherical wave incidence is theoretically analyzed and insulation mechanisms are considered. The displacement of the plate is formulated using the Hankel transform in wavenumber space and the transmitted sound pressure in the far-field is obtained by Rayleigh's formula in an explicit closed form. Moreover, a reduction index is also derived in a closed form by introducing an approximation into the vibration characteristics of the plate. Deterioration of the insulation performance under the spherical wave incidence is caused by an apparent decrease of wall impedance that depends on the directivity of the transmitted sound wave. The mass law for a spherical wave incidence is different from that for a normal plane wave incidence: doubling the weight of the wall or the frequency gives an increase of 3 dB (c.f. 6 dB for a normal plane wave incidence), which is also smaller than the field incidence mass law.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.