Modelling and optimization of the sound absorption of wood-wool cement boards

The present article aims to characterize and improve the sound absorption of wood-wool cement boards (WWCB) with varying strand widths, densities, thicknesses and applied with varying air cavity thicknesses by using impedance models. Different rigid-frame impedance models were analysed to predict the acoustic impedance of this material, and their suitability for the WWCB was evaluated. The Johnson-Champoux-Allard (JCA) model with its parameters, porosity, flow resistivity, tortuosity and characteristic lengths, was found to be the most appropriate to model the normal incidence sound absorption. The relations between the bulk density of the board and the impedance model parameters are established for material characterisation and optimization. Optimum density values were found per strand in terms of the sound absorption in the frequency range 200-2500 Hz. Moreover, the use of a density variation in the boards leads to improvement of the sound absorption. Regarding the application of the board, the use of an air cavity with a thickness of 100 mm leads to an optimized sound absorption for every strand width.