Sound absorbers with micro‐perforated stretched foils and porous materials

At the spring meeting 2004 in New York first results for the sound absorption of micro‐perforated stretched foils have been presented. The classical set‐up of a micro‐perforated sound absorber consists of a micro‐perforated panel in front of an air cavity. The sound absorption coefficient of these set‐ups can easily calculated with a high accuracy according to the well‐known approximation of D.‐Y. Maa if all defining geometrical parameters (diameter of microperforation, distance between orifices, panel thickness and air cavity depth) are known. In this contribution measured sound absorption coefficients of other set‐ups with micro‐perforated foils as well as combinations with different porous materials will be presented. For these assemblies no closed calculation model exists so far. Comparisons between computer‐based calculations of layered absorber set‐ups show promising results for some assemblies. Finally different applications in various rooms will be presented. As expected the comparison between the...