| Abstrakt: |
Measurements were performed, under semireverberant conditions, to examine uncertainties in the two-microphone cross-spectral method for determining acoustic intensity. Calculations of the pressure gradient error, the error associated with the correction for phase mismatch, and the cross-spectrum random error are discussed. The results of preliminary tests performed under free-field and plane-wave conditions are also presented. The influence of semireverberant conditions on the accuracy of the intensity measurement was studied through the use of a standing-wave tube as a reference sound source. With the tube source placed in a 112-m3 room having reverberation times of about 0.5 s, the radiated power was determined both from the intensity measured inside the tube and from the intensity integrated over a spherical surface enclosing the source. For a measurement system configured to limit the errors listed above to 0.5 dB under free-field conditions, phase correction and random errors of several decibels occurred for measurements in the semireverberant room, when determined for the individual frequency components of the Fourier analysis spectrum. However, the calculated 1/3-octave-band sound power levels agreed within ±0.5 dB for the bands from 160 to 630 Hz. Reductions of the errors by selecting a probe configuration to increase the cross-spectrum phase, increasing the number of time records sampled, and, for measurements within a tube, increasing the tube radius are discussed. [ABSTRACT FROM AUTHOR] |
