Sound radiation efficiency of honeycomb and sandwich plates

There are many possible applications for sandwich and honeycomb structures in the vehicle and building industry. However, a lightweight and stiff honeycomb structure has often poor acoustic properties. It is therefore essential that some acoustic properties can be predicted and optimized. It has been found that the so called apparent bending stiffness of a composite structure is strongly dependent on frequency. The frequency dependence can be determined based on a sixth order differential equation governing the bending of the structure. In the model used, shear and rotation in core are considered. The frequency dependent bending stiffness can be determined by means of simple measurements on beams or through point mobility measurements on plates. Previously it has been shown that the sound transmission loss of a sandwich structure can be well predicted using conventional theoretical models for single leaf panels by exchanging a constant bending stiffness with a frequency dependent apparent bending stiffness. A similar approach has been followed to predict the sound radiation efficiency of sandwich or honeycomb structures by inserting a frequency dependent bending stiffness in Leppington's classical theory. Predicted sound radiation ratios are compared to full scale measurements on honeycomb structures. The agreement between predicted and measured results is satisfactory.