Sound power determination from surface intensity measurements on a vibrating cylinder

Abstract

The feasibility of using surface intensity measurements for the determination of sound power as a tool for noise source identification was studied with an experiment on a circular cylinder. This cylinder was an idealized model of a muffler shell of a heavy diesel truck. Two experiments were performed with the cylinder excited by an electromagnetic shaker. In the first one, the shaker was driven with a one-third octave band of white noise centered at 6300 Hz and in the second experiment it was driven with broadband white noise between 1000 and 5000 Hz. The sound power measurements were made in a reverberant room and the reverberant room method was used to provide a comparison with the sound power levels obtained from the surface intensity measurement. The acoustic surface intensity was computed from the cross-spectral density between the acoustic pressure and the normal surface velocity of the cylinder. An equation was developed to allow for inclusion of a correction for phase shifts that were caused by the instrumentation and by the finite distance between the microphone and the vibrating surface. The phase shift resulting from this distance was found to have a dominant effect in the higher frequency range and it was important to make these phase-shift corrections in order to obtain accurate measurements of sound power. After including these phase-shift corrections, reasonably good agreement was achieved between the sound power levels obtained from the surface intensity measurements and those from the reverberant room method.

Development of a hand-held sensor probe for detection of sound components radiated from a specific device using surface intensity measurements

“…The surface intensity method is used to measure the structure-borne sound propagated from machinery or radiated from the surface of a vibrating structure [2][3][4]. This method is a promising technique for sound power measurements of individual noise sources in the presence of a noisy sound field [5,6].…”