A standard type of sound absorbing ceiling elements manufactured by DAMPA,Denmark, is constructed of a perforated metal plate, a thin plasticmembrane, and a layer of mineral wool. Tests made by the manufacturer indicatedthat although the mineral wool was removed, the sound absorptionof the elements was preserved to a certain extent. In order to investigatethe sound absorbing properties of this new type of element the absorptioncoefficients for a large number of test specimens were measuredin an impedance tube. Based on the measurement results a simple theoreticalmodel describing the sound absorbing properties was developed.
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