Prediction of sound reduction index of plenum window by the surface impedance approach

The paper predicted the sound reduction indices (SRIs) of plenum windows with various configurations by the surface impedance approach (SIA). Assuming that the glass panes of plenum windows are rigid, two spaces connected through a plenum window can be taken as a three-coupled space. In terms of a multiply connected space, the SIA enables to characterize the acoustical properties of each sub-space by its own descriptors – blocked pressure and surface impedance across the coupling interface surface between any two sub-spaces. With the descriptors identified, the sound radiation in the entire space can be predicted accordingly. The sound radiation due to a point source in an acoustical space consisting of a rectangular space, a plenum window and a semi-free space was successfully predicted by the approach. Providing the diffuse sound field is generated in the rectangular space, the SRIs of plenum windows could be determined with the predicted averaged sound pressure level in the diffuse source space and the predicted sound intensity level across a prescribed measuring surface in the receiver space, i.e., the semi-free space according to the standard ISO 15186–1. The SRIs of five plenum windows were studied by the SIA. The predicted results are in good agreement with the measured ones obtained in the laboratory environment, which indicates the feasibility of the SRI prediction by the SIA.