Experimental transmission loss investigation of sandwich panels with different honeycomb core geometries

Political Requirements like CO2 reduction lead to highly sophisticated design in aerospace engineering. Nowadays, structural components are multi-material composites, which combine a low mass with a high stiffness. The disadvantage is often an increased sound transmission due to these properties. Geometry variation of a honeycomb core in a sandwich panel is a promising approach to influence the transmission This paper presents experimental results of the transmission loss (TL) measurements for sandwich panels with different honeycomb cores of identical mass. A diffuse sound field from a reverberation room excites the sandwich panel and in the neighboring anechoic room the intensity is measured. This setup allows a narrow band TL measurement. Previous simulation studies show a shift of the Eigenfrequency dips in the TL up to 1000 Hz. This shift is not observed in the experiments probably due to the inherent damping. Nevertheless, the experiment shows a coincidental dip for a core with large cell diameter in the regarded frequency range, which depends on the core geometry. Also, the TL of this large cell core is higher compared to the other sandwiches for the frequency above the coincidental dip. This may allow preventing transmission in critical frequency bands for future aircrafts structures