The increase of the sound absorption through rectangular slot perforations

This paper describes several methods to predict the sound absorption of a surface with rectangular perforations. Theoretical and experimental works about rectangular perforations are reviewed and compared. In particular, the transfer matrix method is considered together with possible expressions for the surface, hole and cavity impedances. In this model, the surface impedance may be calculated summing resistance and mass terms to the characteristic impedance. Besides, fundamentals of models for numerical cavity modes, for microperforations and for double-porosity are described. A comparison of all previous models is also reported. Then, the paper shows the results of a few measurements of sound absorption of walls where rectangular slot perforations have been left between stone elements. Comparisons with theoretical models are carried out to explain different mechanisms of absorption. Finally, this paper aims to establish practical methods to develop broadband sound insulation devices through rectangular perforations. © 2013 Acoustical Society of America.