NUMERICAL AND EXPERIMENTAL INVESTIGATION OF THE PERFORMANCE OF SOUND INTENSITY PROBES AT HIGH-FREQUENCIES

The influence of scattering and diffraction on the performance of soun d intensity probes has been examined using a boundary element model of an axisymmetric two-microphone probe with the microphones in the usua l face-to-face arrangement. On the basis of calculations for a variety of sound field conditions and probe geometries it is concluded that t he optimum length of the spacer between the microphones is about one m icrophone diameter; with this geometry the effect of diffraction and t he finite difference error almost counterbalance each other up to abou t an octave above the frequency limit determined by the finite differe nce approximation. This seems to be valid under virtually any sound fi eld condition that could be of practical importance in sound power det ermination. The upper frequency limit corresponds to about 10 kHz for an intensity probe with 1/2-in. microphones, which means that it shoul d be possible to cover most of the audible frequency range, say, from 50 Hz to 10 kHz, with a single probe configuration. The numerical resu lts have been confirmed by a series of experiments. (C) 1998 Acoustica l Society of America. [S0001-4966(98)04202-7].