Determination of The Scattering Parameters of Fittings in Industrial Buildings for Use in Computer Based Factory Noise Prediction Models: Part 2 – Scale Model Experiments

In a companion paper results obtained from computer simulation1 have demonstrated that the sound propagation characteristics of disproportionate rooms are determined by the product of the fitting parameters scattering cross-section (Q) and absorption coefficient (αobst) of fittings. It was also proposed that the absorption of a fitting as measured in a conventional reverberation chamber is equivalent to four times the product of those two parameters. This suggests that measurement of fitting absorption in a conventional reverberation chamber could provide the data required for input into current computer based factory noise prediction models. Since both parameters are required as inputs to computer models it would be necessary to separate them in some way from the data obtained in the reverberation chamber. In this paper two methods for determining the scattering parameters of fittings in industrial buildings based upon acoustical measurements are described. The accuracy of these is compared with that resulting from the application of a geometrical measurement method to determine the scattering cross-section (Q) of various shapes of model scatterers employed in experimental work employing 1:20 acoustic scale models. The values of Q obtained from each method were used to predict sound characteristics a model disproportionate chamber using RAYSCAT. The predicted results obtained from the computer model by inputting the values of Q determined using the acoustical measurement methods were found to be more accurate than those using the geometrical measurement method.