Predicting the Sound Transmission Loss of Honeycomb Panels using the Wave Propagation Approach

The sound transmission properties of sandwich panels can be predicted with sufficient degree of accuracy by calculating the wave propagation properties of the structure. This method works well for sandwich panels with isotropic cores but applications to panels with anisotropic cores are hard to find. Honeycomb is an example of anisotropic material which when used as a core, results in a sandwich panel with anisotropic properties. In this paper, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principle directions. These calculated wavenumbers are validated with the measured wavenumbers estimated from the resonance frequencies of freely hanging honeycomb beams. A combination of wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. These predictions are validated through sound transmission measurements. Passive damping treatment is a common way to reduce structural vibration and sound radiation, but they often have little effect on sound transmission. Visco-elastic damping with a constraining layer is applied to two honeycomb panels with standard and enhanced fluid coupling properties. This enhanced fluid coupling in one of the test panels is due to an extended coincidence range observed from the dispersion curves. The influence of damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal panel are very similar.