If machines or apparatuses radiate partially coherent sound waves, locating their sources can be performed by the reconstruction of an acoustical hologram produced by the waves themselves. Since the practical spectrum of the sound fluctuates, a time average of the hologram signals can be taken, and a lock-in amplifier is used for the purpose. Using rotating gears as a test object, an experiment based on this principle has been successfully carried out to obtain the distribution of radiation sources at a frequency of 9·9 kHz.