Fluctuation theory of thermal acoustic radiation

Wave statistical theory of the thermal acoustic radiation in a medium is presented on the basis of a model of hydrodynamic fluctuations. The wave stochastic equation is derived for the pressure fluctuations with given random mechanical forces. This theory is applied to the problems of the thermal fluctuations of the pressure in (1) an unbounded medium and (2) an acoustic resonator while taking into account the directivity diagram of a transducer. In the case of a resonator, the conditions for measuring of separate resonance peaks are estimated depending on the ratio of the transducer and the resonator dimensions and values of absorption of a medium. (C) 1996 Acoustical Society of America.