Many materials used for the construction and furnishing of buildings are required to have sound absorption properties aimed at preventing either echo phenomena or sound transmission to other parts of the building. Methods have therefore been developed to measure sound absorption in the laboratory. However, in many cases the value obtained is dependent upon the design of the measuring room. Moreover, values of greater than 1, which are theoretically impossible since they imply that more sound is absorbed than is incident, are frequently obtained.
The aim of the project is to develop a series of artefacts whose sound absorption characteristics are known both theoretically and experimentally. Techniques will then be developed to characterize measuring rooms and thus enable comparable sound absorption values to be obtained in different laboratories.
Flat reference absorbers have been developed for which it is possible to determine both theoretically and experimentally the 'true' sound absorption coefficients. Work is continuing to investigate the sound absorption coefficients that are actually measured with these reference absorbers in different reverberant rooms.