Theory of a two source-location method for direct experimental evaluation of the four-pole parameters of an aeroacoustic element

Abstract

A new method, called the two source-location method, is described for measurement of the four-pole or the transfer matrix parameters for an acoustic element or a subsystem of elements by means of the four-microphone technique and use of the transfer function approach. Theoretical expressions are derived for the two source-location method, and these are shown to be identical to those for the two-load method. However, the two methods are conceptually different. The two-source method is shown to be functionally much more stable and entirely independent of the loading terminations. An uncertainty analysis is presented and used for estimation of possible nonequalization errors in the transfer matrix parameters. Finally, several examples of successful measurement use of the new method are included.