Building components and materials for low frequency airborne and structure-borne sound insulation

During the last years it has been observed a growing interest in the characterization of the acoustical performances of building elements at low frequencies. The proposal to extend measurements and ratings, in the frequency range from 50 Hz to 100 Hz (in small rooms) involves considerable experimental difficulties, and many papers have been published by various research groups, focused on this topic. In any case, experimental results show high uncertainties and the acoustical performances of the tested partitions are often unclear. Furthermore, many typologies of insulating systems (for both structure-borne and air-borne sound insulation) commonly used in dwellings, have structural resonances at that frequency range, allowing experimental data to be more inaccurate. It follows that, as a first observation, the actual acoustic insulation properties of such systems are not effective enough under the structural resonance. Except some special applications, in which peculiar insulation systems are adopted (such as box-in-abox systems for listening or recording rooms or seismic systems), the common partitions significantly insulate the medium or high frequencies, but are inefficient at very low frequencies. A general review of the recent literature (and also of the commercial proposals) clearly shows this lack. In this work, in very general and qualitative terms, the technical issue of achieving efficient insulation system at low frequencies, both for air-borne sound insulation and for structureborne sound insulation is addressed. Acoustical performances are analysed on the basis of traditional calculation models and experimental evidences.