A range of flat hot-compacted single-polymer composite panels made from oriented polypropylene and polyethylene with differing dynamic modulus and damping capacity were freely suspended and subjected to mechanical excitation, allowing their acoustic frequency response over the audio bandwidth to be measured. The audio response over selected bands was correlated with the dynamic modulus and damping capacity measured in bending in these materials and compared with the response of a traditional composite material, namely, carbon-fiber-reinforced epoxy resin. Low damping and high dynamic modulus were found to result in relatively high output levels from the hot-compacted flat panels, which contrasted with the results previously measured on a traditional cone-shaped speaker made from a hot-compacted polypropylene material, which found high damping to be advantageous. The results of the current study on flat panels are explained in terms of mechanical impedance of the panels and their corresponding efficiency. It was concluded that the best flat-panel audio response came from compacted polyethylene sheets, which combined high stiffness, low density, and a low level of damping. (c) 2005 Wiley Periodicals, lnc.