Sound reduction index prediction of double-layer gypsum panels through the transfer matrix method

Gypsum board walls are widely used in today's buildings. A possible way to considerably increase the sound insulation performances of such lightweight walls is to apply double-layer gypsum panels screwed together. Being the boards separated by a thin air gap, there is no shift of the critical frequency from the single-layer case. Moreover, it is possible to obtain an improvement of the sound insulation performances provided by the additional mass given by the double layer. The thin air layer is, however, responsible for a loss of acoustic performance due to the cavity resonance effect in the frequency range between 800 and 1600 Hz. In this article, the increase in the acoustic insulation achieved through the use of coupled gypsum boards is studied and a modelling technique based on the transfer matrix method is used to simulate the acoustic behaviour of the resulting structure; in particular, the thin air layer between the coupled boards is modelled. The simulations are compared with laboratory measurements carried out according to the international standard series ISO 10140. The transfer matrix approach is found to be suitable to describe the problem, provided that a modified model for the air gap between the boards is applied.