Sound transmission loss of honeycomb sandwich panels

Honeycomb sandwich panels used for commercial applications are typically stiff and lightweight. They are optimized for mechanical performance, but have poor acoustical performance. Transmission loss (TL) is one of the metrics used to assess the acoustical performance of honeycomb sandwich panels. Transmission loss for these panels shows inferior mass law performance above coincidence frequency for commercially available panels. For superior transmission loss performance, it is critical to delay (maximize) the coincidence frequency, which is determined by the dispersive panel bending waves. Panel bending waves are characterized by three frequency regimes - total panel bending, core shear, and individual skin bending. These regimes are controlled by panel geometry, panel mass and elastic properties of the core and the skins. The coincidence frequency can be increased by designing panels with core shear wave speeds that are subsonic. In the present study, the influence of different panel design parameters, such as core density, core material, cell size, and cell structure, on the transmission loss of honeycomb sandwich panels is analyzed. Moreover, TL results of panels in three classes of core shear wave speeds - subsonic, transonic, and supersonic - are presented. For panels with supersonic shear wave speed, core density influences TL above the coincidence frequency, but other parameters like cell size and skin type show negligible effects. Panels with subsonic and transonic core shear wave speeds show improved acoustic performance compared to their supersonic counterparts. The mechanical performance of subsonic and transonic panel designs is generally inferior but can be improved when accompanied by weight increase.