Experimental investigation on sound transmission through cavity-backed panels

A considerable amount of information has been developed in architectural acoustics on sound transmission through panels. Emphasis has been on high-frequency transmission where “mass law” is applicable and coincidence effects are important. However, there has been only limited attention given to low-frequency sound transmission. Low-frequency sound transmission is stiffness controlled in the frequency region below structural resonances, and damping and stiffness controlled at resonances. Furthermore, the closed receiving room (cavity) behind the panel may have a significant effect on the panel dynamics and, therefore, the sound transmission. A panel backed by a closed cavity provides a meaningful model for studying low-frequency sound transmission of the type encountered in aircraft for example. Although some theoretical work has been done on the subject, only limited experimental data are available in the literature. The purpose of this paper is to present some experimental findings on the effects of panel stiffness and receiving space absorption on low-frequency sound transmission through panels into closed spaces. In addition, a simplified method for calculating the low-frequency noise reduction of a cavity-backed panel will be presented.