The acoustic sealing of holes and slits in walls

Abstract

The sound transmission through circular holes and through long slits in a wall of finite thickness is computed for oblique plane waves. These openings may be filled by porous absorber materials and/or they may be sealed at their end planes by plastic sealing layers. The absorber materials are modelled by their acoustic characteristic data (propagation constant and wave impedance) and the sealing layers are represented by masses. The analysis is treated as a boundary problem. The final quantities are the transmission coefficient or the transmission loss. Numerical results show the influence of the design parameters. It is found that the performance of openings with a porous and/or plastic sealing cannot be approximated by the results for empty and open holes or slits. As a result of these studies it is recommended to use a transmission loss of the hole reduced by its cross-sectional area and to use a transmission loss of the slit reduced by its width as the final quantities, once the sound transmission through such openings should be standardized. These reduced transmission losses are nearly independent of the area under most conditions of parameters and frequency.