The calibration of sound intensity instruments—in particular, with respect to instruments' sensitivity to both sound intensity and particle velocity in the rated frequency range—is challenging for laboratories worldwide. The commonly used approach is to measure the pressure sensitivity and phase difference of a pair of microphones, and electrically test the analyzer. The intensity instrument cannot be fully calibrated if only the components of the intensity measurement system are calibrated. Ideally, the sound intensity instrument should be calibrated as a system, along with all its parameters being compared with traceability to recognized standards; this will increase the confidence in the validity of measurement results. Currently, calibration below 50 Hz is still not feasible. To meet this requirement, the Beijing Aerospace Institute of Metrology and Measurement Technology has developed a double coupler calibration system capable of generating an intensity or particle velocity level of known amplitude and direction traceable to recognized standards. This paper covers the principle of the double coupler technique, design of the system, and generation of the reference intensity signal. The calibration results are in good agreement with the theoretical calculation results.
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