Research On Some Key Problems Of The Measurement Of Sound Power By Scanning Sound Intensity

Sound Intensity is the sound wave intensity in sound field, which equals sound energy through the unit area perpendicular to the energy flow direction. Since the sound intensity is a vector in nature, which has the priority to sound pressure when used to describe sound field. Sound power determination using sound intensity methods can be categorized into the discrete point and scanning measurement methods. In this dissertation, the rectangle measurement plane is chosen, and convergence of rectangle, linear plus half circle and saw-tooth shaped scanning ways has been verified in theory. Meanwhile the relationships between the sound power measurement error and the scanning velocity, the size of the scanning plane, the distance from sound source to scanning plane, the scanning density have been investigated deeply. The errors of the two-microphone sound intensity measurement system have been analyzed and evaluated, the reduction methods of the measurement error has been described and utilized to correct the measurement system. In order to solve the high frequency cut-off problem that exists in the sound intensity determination using arithmetic-averaging sound pressures, many types of sound source have been adopted and sound intensity determination methods using arithmetic averaging and geometrical-averaging sound pressures have been compared. As a result of the analysis, the applicable scopes and characteristics of these two methods have been given in this dissertation. To testify the theoretical research, some experimental researches on the effectiveness of selecting rectangle measurement plane and the convergence of the three scanning ways have been conducted in the common and half-anechoic chambers respectively.In chapter one, the research meaning has been described, and the development history and current status of the sound intensity measurement technology have been reviewed, and the contents of this dissertation have been determined.In chapter two, wave motion equation, sound energy, sound energy flux density, sound intensity and its scaling method and the theorem of two-microphone sound intensity have been introduced. The theoretical, manufacture and random errors of the two-microphone sound intensity measurement has been analyzed in details, and the measurement reduction method has been given based on the evaluation of the measurement system using uncertainty theorem. The error functions of the two-microphone sound intensity measurement system has been deduced according to the transfer function, and the residual sound intensity method has been used to correct the sound intensity measurement system.In chapter three, the convergence of scanning sound intensity method determining sound power has been investigated, and the correctness of the rectangle, line plus half circle and saw tooth shaped scanning ways have been verified to be real scanning ways on a rectangle measurement plane. Meanwhile, this dissertation study if there are other real scanning ways that can be used to precise measurement results, the relationship between the reality of the scanning ways and the scanning velocity, the relationship between the sound power measurement convergence velocity when using the three scanning method aforementioned and the scanning type and scanning velocity, the relationship between the size of the scanning plane and the scanning errors. When the saw-tooth shaped scanning method is used on the rectangle measurement plane, the minimum value and value scope have been given according to three different sound source error values.In chapter four, in order to solve the high frequency cut-off problem that exists in the sound intensity determination using arithmetic-averaging sound pressures, the calculation methods based on the arithmetic and geometrical averaging sound pressures have been compared at the aspects of the calculating precision and quantity, and their applicable scopes have been given, where different kinds of sound sources are selected such as point source, planar sound field, monopole, dipole, quad-pole, vibrati...