A MEASUREMENT METHOD FOR DETERMINING THE SOURCE DATA OF ACOUSTIC 2-PORT SOURCES

Acoustic source data for fluid machines are of importance for calculating the acoustic field generated in a duct system and for analysis of source-load interaction effects. In this paper the problem of measuring source data for acoustic two-port sources in general is first described and critically discussed. A measurement method to determine the source data of an acoustic two-port source in the form of a source strength vector and a scattering matrix is then presented. This method consists of two steps. First the scattering matrix is determined by using external noise sources to create two independent acoustic test cases. As the second step, the source strength is determined by using a number of different acoustical loads to obtain an overdetermined problem. By solving the overdetermined matrix problem one can improve the prediction of the source data and it is also possible to verify whether or not the machine under test behaves as a linear source. For this purpose a special linearity measure has been defined. The measurement method has been verified and also successfully tested on an axial flow fan.