The revision of the ASHRAE-36 standard required the improvement of the method of measurement of sound power at discrete frequencies. One of the means by which the accuracy of the sound power measurement can be increased is the rotating vane and therefore the research concentrated on its application for this purpose. In order to perform the study of the vanes, the statistical properties, which determine the accuracy of measurement, have to be studied f i r s t . Although theoretical relations for the statistical propei'ties of the sound fields at single frequencies were recently developed, their applicability had to be experimentally verified. Deviations from the diffuse sound field even at high modal densities were found. Major effort was concentrated on the explanation of the principles of the modulation of sound field by rotating vanes. It has been found that the vane provides the frequency and amplitude modulation of the sound field. Simple theory of the frequency modulation was worked out and experimentally verified. The effect of combined modulation was studied in terms of spectra generated by the vane action.