A Design And Analysis Theory Of The Acoustic Diffuser Based On Micro-perforated Plate

Sound diffusion is an important branch of the acoustic research, using sound diffusion structure can get a good consistency acoustics. Quadratic residue sequence diffuser(QRD) is a very widely used sound diffusion structure, as for its simple structure, convenient proliferation and excellent diffusion performance. Micro-perforated panel absorber structure, first proposed by famous acoustics Maa, is a widely used sound absorbing structure because of its excellent features. In this paper, the micro-perforated plate acoustic theory and the thin plate vibration theory are studied and a micro-perforated plate with back wall model is proposed, by solving the acoustic impedance of the structure and matching it with the acoustic impedance of the QRD so that the model has similar diffusion characteristics with QRD.Firstly, the single-layer micro-perforated plate with back wall model is analyzed. Plate vibration equation under the action of acoustic wave is established, according to Maa and Takahashi’s micro-perforated plate acoustic theory. The acoustic impedance of the finite micro-perforated plate is obtained by using modal superposition method combined with micro-perforated plate fluid-structure interaction boundary conditions. Then the plate parameters of the nonlinear equation is established, giving the appropriate sheet size, making the acoustic impedance of the plate equal to the local acoustic impedance of QRD slot. As examples, the simply supported and fixed boundary entire circular plate, all edges simply supported square plate are studied and their acoustic impedance frequency characteristic curve are analyzed. The diffusion characteristics are compared between the diffuser composed by micro-perforated plate model and the QRD at different frequencies. The results show that the diffusion characteristic of the proposed model is similar to QRD.Further analysis of multi-layer micro-perforated plate with back wall model is carried out. First, the single-layer micro-perforated plate without back wall vibration equation is established and solved, the reflection and transmission of sound pressure are obtained and transform matrix of single-plate is established. Then, the multi-layer radiation matrix is obtained by the cascading method and further the overall reflection pressure of layers is obtained, thus the overall acoustic impedance of the multi-layer plate is obtained. As examples, three kind of micro-perforated plates are studied and their acoustic impedance frequency characteristic curve is analyzed, and the diffusion characteristics of diffusion plate composed by micro-perforated plate model and the QRD diffuser plate at different frequencies are compared. The results show the correctness of the cascade method and the diffusion characteristic of proposed model is similar to QRD, however smaller in size.