GAUS, Mech. Eng. Dept., Univ. de Sherbrooke, Sherbrooke, PQ J1K 2R1, Canada
Originally, an acoustic cavity has been designed and fabricated to study active noise control strategies in a closed volume. It has a parallelepipedic shape of dimensions 0.868 mx1.15 mx1.0 m with walls made of 13-cm-thick reinforced concrete. The top is closed with a simply supported 6.63-mm-thick aluminum plate. The plate support was carefully designed to meet the simply supported boundary conditions. The plate is excited by a point force and its structural response is measured with force and accelerometer transducers. The acoustic field inside the cavity is also measured using microphones. Comparisons between calculated and measured natural frequencies of the plate shows that for most of the modes found in the 0--500 Hz range, the discrepancy is less than 1 Hz. Quadratic mean surface velocity and mean volume sound pressure have been calculated from frequency response functions measured for centered and off-centered point force excitations. Comparisons with calculated values shows very good agreement. The relative contribution of the various plate modes and cavity modes are well distinguishable.