Diffraction errors at sound intensity measurement
The known systematic errors caused by finite-difference approximation and a divergence of phase characteristics of receivers' channels are inherent in a sound intensity measurement method by means of two microphones. Mutual influence of receivers owing to diffraction effects results in occurrence of new type of systematic errors. Diffraction can influence to a result of sound intensity measurement by two ways: by means of distortion of a pressure field of an incident wave by its dispersion on the other receiver included in a pair and by means of influence of change of acoustic resistance of receivers on their sensitivity. The error because of distortion of sensitivity of microphones increases at the small wave sizes of distance between transducers and decreases when the distance between microphones increases. The error owing to diffraction distortions of the pressure is taken into account together with an error of finite-difference approximation. This error increases with growth of wave distance between transducers. These two effects limit a frequency range of intensity measurements at low and high frequencies. Relative reduction of microphone sizes results in shift of intensimeter working range to higher frequencies. The obtained dependencies of diffraction errors of intensity measurement allow to choose a working range of the wave sizes of a distance between microphones. The relation between measured and true intensities allows to take into account the distortion of measured values, induced by the device, during processing of measurement results.
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