Improvement of sound insulation and absorption performance without increasing weight or thickness has always been the pursuit of the acoustical society. For an acoustical wave in the low frequency range, neither insulation nor absorption is easy to be dealt with by a thin structure, because the noise insulation is restricted by the so-called mass law and the absorption is limited by the reactance of structural input impedance. In both cases, to achieve effective results, the mass of structures need to be handled properly. This lecture outlines the ongoing effort to improve sound insulation and absorption for lightweight structures. Besides, examples on the vibro-acoustic properties of lightweight plates subject to typical excitations are presented, and novel structures designed for low frequency sound absorption are also reported and discussed.
