This paper reviews general methods of identifying noise sources in machinery and in particular it describes in detail two methods which have been studied by the authors on a truck: near field measurements and the coherence technique. The results of these two methods are compared with results of a third method in which the same truck with different sources wrapped and then sequentially exposed was driven past a microphone using the SAE J366b test.
The paper also reviews two different stationary indoor standard tests which have been investigated: the reduced drive-by simulation method, and the sound power method. These tests could be used to supplement (or replace) the standard SAE J366b drive-by test in some cases. Comparisons are made of data from the two tests developed and the SAE J366b drive-by data for the same truck.