Wideband sound absorber obtained by combination of two microperforated panel absorbers with different air-cavity depths arranged in parallel

摘要

Microperforated panel (MPP) sound absorbers are widely known as one of the most promisingnext-generation sound absorbing systems. MPPs are usually used with a uniform depth of the aircavity. MPPs offer high absorptivity at mid-high frequencies, however, absorption frequencyrange is limited because of their nature as Helmholtz-type resonator. In this paper, the authorspropose a combination of two MPP absorbers with different air-cavity depths arranged in paralleland discuss its potential for achieving a broader absorption frequency range. First, measurementsof the normal sound absorption coefficient using standing wave tube are carried out for two typesof configurations of the back cavity: one is the case of the two cavities with a partition, and theother is not partitioned. Next, electro-acoustical equivalent circuit analysis is made for thesespecimens, and their sound absorption characteristics are discussed through both theexperimental and calculated results focused on the excess absorption. Finally, the reverberationsound absorption coefficient of MPP absorbers by combination of two different air-cavity depthsis also measured. The effect of the period and pattern of the arrangements on the excessabsorption is discussed.