Double-layer gypsum panels: Prediction of the sound reduction index using the transfer matrix method

Gypsum board walls are widely used in buildings today. A possible way to considerably increase the sound insulation performances of such light-weight walls is to apply a double or triple layer of screwed boards separated from each other. The separation between the boards prevents the decrease of the critical frequency towards lower values, while retaining the improvement of the sound insulation performances provided by the double layer. In this paper the loss of acoustic insulation performances due to the thin air layer between the coupled boards is studied and a modelling technique based on the transfer matrix method is used to simulate the acoustic behaviour of the resulting structure. The simulations are compared with laboratory measurements carried out according to the ISO 10140 series standards, and 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 used.