Distributed Sound Source And Its Application In Active Acoustic Structures

The traditional passive noise control which comprises of the source control, path control and the received point control, in general, is not very efficient at low frequencies and hence active control of low frequency sound radiation has been studied. In recent years there has been much interest in the active acoustical structure. In this thesis, the study is focused on the characteristics of distributed sound source and its using in the active acoustical structure as the secondary source, including the following four aspects.Firstly, comparison between lumped and distributed sound source indicates that the distributed sound source is suitable than the lumped sound source when used as the secondary sound source in active noise control. A mathematical model of planar sound source has been presented.Secondly, the characteristics of distributed sound source are analyzed, the applications of the clamped plate in active acoustic structure are also studied, and then its theoretical model used as the secondary sound source in active noise control is developed.Thirdly, based on the simply supported plate used in the active acoustic structure, the influences of the plate parameters and the different kinds of excited forces on active acoustic structure are presented. According to the simulation results, the rules of the secondary sound source design have been introduced.Lastly, the plate's vibration modes and natural frequencies have been experimentally measured by LMS test Lab. Active control of sound radiation from rectangular plate by planar sound source is also investigated experimentally. The measurement of sound radiation power and sound intensity before and after control is conducted in the anechoic chamber, the experimental data show that the control performance is efficient. In addition, the influences of the secondary panel area on active control have been discussed.