Simple method to determine the transmission loss of gypsum panels

In recent years, a new technique for the determination of the transmission loss of sandwich panels has been applied to simple and composite building materials. The method is based on a model which, given an anisotropic panel, requires physical and mechanical properties of the materials making the structure and the natural frequencies of two beams cut from the plate, orthogonal directions, to determine its sound transmission loss. A simple test procedure can be used to measure the frequency response functions (FRF) of the two specimens. The beams are suspended in free-free conditions and an accelerometer is placed at one side. An impact hammer is used to excite the specimen to the other side, while an analyser correlates the data from the transducers. Once incorporated in the mathematical model, these simple input data allow to compute the bending stiffness of the beams, the critical frequency of the panel, the internal and the radiation losses and, finally, the panel transmission loss. The radiation losses of the panel are estimated according to Maidanik’s work. A software has been developed to implement the mathematical model and several experimental measurements have been performed in order to validate it. One series of tests has been carried out on some gypsum panels, testing them in a laboratory using sound transmission rooms and the previously described model. Finally, a panel placed between the two rooms and moved by a shaker was used to measure the sound intensity and the vibration velocity levels through a probe and a set of 9 accelerometers. The purpose of the test was to make an estimation of the sound radiation ratio. Predicted and measured results are compared. The agreement is fair.