Robert Hickling
Wei par Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
A vector sound-intensity probe can be used to measure the sound-power of a moving source that has an axisymmetric sound field. The source moves along the axis. The vector probe measures intensity normal to a hypothetical cylinder coaxial with the source path and simultaneously tracks the source. In this way it is possible to determine the intensity (sound-power per unit area) distribution over the surface of a long cylinder enclosing the source. If the cylinder is long enough, the contribution of the ends can be neglected and the intensity distribution can be integrated to obtain the sound power of the moving source. This procedure was applied to a small moving continuous sound source (i.e., a driven Bruel & Kjaer 8105 hydrophone) in a water tank. The vector sound-intensity probe consisted of four hydrophones in the tetrahedral arrangement, intensity being measured with the cross-spectral method [see Hickling et al., J. Acoust. Soc. Am. 94, 2408--2412 (1993)]. Good agreement was obtained between the sound power of the moving source, the sound power of the source when stationary and the sound power of the source estimated from information provided by the hydrophone manufacturer.