Research On Measurement System Based On Digital Sound Intensity Probe And Error Analysis

After reviewing and analyzing the sound intensity measurement theory and the existing sound intensity measurement systems thoroughly, in this dissertation a sound intensity measurement system was first proposed based on a digital sound intensity probe. Compared with the traditional analog, the front-end conditioning circuit is optimized and both a digital circuit based on SOC framework and a closed-loop calibration control circuit are highly integrated in the digital sound intensity probe. The proposed measurement system can directly output the corrected narrow band spectrum of sound intensity, the CPB spectrum as well as the total sound intensity level. By connecting external amplifier and speaker, the self calibration system of sound intensity probe can be also constituted. The design of the proposed measurement system based on digital sound intensity probe changes the structure of conventional sound intensity test system and resolves the deficiencies of analog p-p sound intensity probe such as bad general characteristics of interface, poor anti-interference, difficulty in parallel and high cost of test system.In order to develop a sound intensity measurement system based on digital sound intensity probe, the problems including hardware design, measurement algorithm and error analysis of sound intensity, software development, calibration method and measurement precision were studied in-depth in this dissertation. The main contents of the dissertation are as follows:In chapter one, the development history and the current status of measurement technique of sound intensity were reviewed; the classification, the characteristics and the development trends of measurement systems of sound intensity were discussed. Then the deficiencies of related products were pointed out and the main research contents of this dissertation were determined.In chapter two, three basic governing equations for continuum were introduced and the relationships among acoustic energy, acoustic energy density and sound intensity were analyzed. The characteristics of sound intensity measurement methods based on both p-u and p-p were discussed. The time-domain algorithm and the cross-spectral algorithm based on two microphones were also discussed. The error equations of instantaneous sound intensity, active sound intensity and reactive sound intensity were derived. The characteristics and physical meaning of important factors such as δPI,SPI0,Ld,F2and F3were analyzed.In chapter three, the parameter calculation and the implementation of hardware circuit were first described detailedly from the points of preamplifier, programmable gain, high and low pass filter, A-weighted pressure, SOC digital circuits and expansion module. Then several factors that influence the measurement accuracy in hardware of digital sound intensity probe were discussed and analyzed. Finally a design method of hardware system of sound intensity probe was proposed to get good measurement accuracy.In chapter four, the main factors generating errors in the digital sound intensity probe algorithm were analyzed first. Then the way how the factors of measurement noises, the quantitative noises, the spectral interference, the energy leakage, the frequency error and the phase compensation influence the calculation accuracy of sound intensity in the digital sound intensity probe algorithm was investigated. Finally a calculation algorithm for piecewise narrowband spectrum and CPB spectrum of digital sound intensity probe was proposed and the errors that may be generated in the proposed algorithm were also investigated.In chapter five, the calibration method and the accuracy of the digital sound intensity probe were investigated. Based on the acoustic model of microphone, the influence of low-frequency sensitivity to the calibration accuracy of the phase of sound intensity probe were analyzed when the pressure hole was exposed to the sound field and when the pressure hole was not exposed to the sound field, respectively. The measurement error model of sound intensity probe which is p-p and face-to-face was established. Two phase calibration methods of sound intensity probe implemented in anechoic room, vertical method and parallel method, were analyzed and compared. A parallel calibration method was proposed for digital sound intensity probe based on discrete frequency sweeping, which can be used in real engineering environment. By the proposed calibration method, a high phase calibration accuracy of the developed digital sound intensity probe can be achieved in an ordinary environment.In chapter six, the development process of PC application software of digital sound intensity probe was introduced on the Windows platform. The main frame of application, the operating mechanism in different communication modes, the control panel of a variety of applications and communication protocols were discussed in detail.In chapter seven, the key performance indicators of digital sound intensity probe such as A-weighted accuracy, sound pressure-residual sound intensity index, frequency response of sound pressure, frequency response of sound intensity and directivity were tested. The accuracy of digital sound intensity probe was also examined by experiments that compare the results of a standard sound power source (B&K4205) and a domestic rotary vane vacuum pump (Type2XZ-4A) in different acoustic environments. Finally two engineering application examples in which the noise sources were identified using digital sound intensity probe were described.In chapter eight, all the investigations in this dissertation were summarized and the topics that should be studied further in the future were proposed.