Sound transmission loss estimation method by impact testing

In order to estimate sound transmission loss (TL) of walls at low frequencies where the effects of structural vibration modes are dominant, a new approach is developed. It is a hybrid of a numerical simulation of the incident acoustic field and modal testing of the wall. Conventional TL estimations need acoustic rooms which are large enough to realize a diffuse sound field. The main advantage of the method proposed here is that there is no need for large reverberant rooms. In executing this method, linear vibration characteristics of the wall and no holes or slits in the wall are assumed and that only impact data are used. The impact data are processed to extract modal parameters of the wall. Using the modal parameters and assuming a rain-drop force on the wall to simulate a diffuse sound field, the wall response is calculated based on stochastic vibration analysis. The total power radiated from the wall is estimated and as a result, the TL of the wall is obtained. This method is applied in a mockup test of a simply-supported plate. The results showed good agreement with the analytical results based on incident sound plane wave model. As a result, this method is proven to be an effective and reliable tool to estimate sound transmission loss of sound insulation wall at low frequencies.