Active Control on the Acoustic Fields in Duct by combing the Controllable Plate Source with Loudspeaker Source

• Main Authors: Po-Kuei Chou, 周伯奎
• Other Authors: 陳國在
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/83080270179141727482

碩士 === 臺灣大學 === 工程科學及海洋工程學研究所 === 98 === The noise control can be divided into two methods including active and passive noise controls methods techniques.The passive control is used to reduce the acoustic fields at medium and higher frequencies,and the active control is used to reduce those one at low frequencies. In this thesis,it is to combine the controllable rectangular plate source and the controllable loudspeaker source for the Active Control of sound(ANC).A rectangular plate and the loudspeaker used as the secondary source for active noise control in a circular duct are developed. Between them,the rectangular plate is fixed on a steel frame vertically and excited by a PZT which is attached to the middle of plate.The rectangular plate is simple in geometry,light mass,easily to construct and only a modification on the materials already installed on duct is required little. We use FIR digital filter as the main structure of the control system in this experiment and take a single-frequency signal directly from a function generator as the reference input.Coefficients of the digital filter are adjusted by using a LMS algorithm in order to achieve the best performance. From the result of the experiment in this study,when the controllable sources are the rectangular plate and the loudspeaker,a locally maximum attenuation of sound pressure levels by 60 dB is reached,which proves that using the combination of a plate source with and the loudspeaker to adaptively active control of sound field in a circular duct is feasible.