Research And Development Of Sound Field Reconstruction System Based On Spherical Nearfield Acoustic Holography

Nearfield acoustic holography method is an important sound field reconstruction technique;it can be applied in sound source identification,and it has to be applied with a microphone array.The microphone arrayswith different sizes and parameters canbe used to the different acoustic environments.The open spherical array is used to reconstruct the interior radiation of sound field in an enclosed cavity structure whose size is greater than the array,and to reconstruct the exterior radiation of sound field of a source whose size is smaller than that of the array.At present,the theoretical fundamentals of sound source identification system with spherical array are all beamforming method based,which are only applicable for high frequency and far field,and none of them are capable to reconstruct the nearfield sound field of sources inside the array.Having this in mind,the author applied the spherical near-field acoustical holography method to reconstruct the near sound field within low to mid frequency range.In view of two situations above,a LabVIEW platform-based acoustic field reconstruction system is developed based on spherical nearfield acoustic holography,and an open spherical microphone array is designed and developed.The sound field of nearfield space can be reconstructed by the sound pressure data measured by spherical array integrated in this system.The main work of this thesis is as follows:The first chapter introduced background and references this research,the evolution of nearfield acoustic holography techniques as well as spherical nearfield acoustic holography method have been reviewed.The second chapter presented the general solution of acoustic wave equation in spherical coordinate system.Then the principle of sound field reconstruction based on spherical microphone array with spherical nearfield acoustic holography method has been introduced.And the optimum microphone distribution on the spherical array surface at designated points has been determined by spherical t-design integration rules.Chapter three introduced the hardware configuration and software architecture of sound field reconstruction system.The system is testedby the numerical simulation data of sound field reconstruction.Chapter four presents theresults of experiments to verify the accuracy and function of the software,one small speaker and electromotor were taken as target sources,respectively.The test results are illustrated in order to validate the efficiency and accuracy of this system.At last,the research results ofthesis have been summarized;the limitations of the developed system and outlookof the research and development are stated.