Plane Sound Source-based Active Noise Control

In the past decades, active noise control has been developed rapidly, which can overcome the disadvantages of passive noise control techniques. However, it is the main difficulty how to make the technique of active noise control applying in the engineering successfully because of its complicated system. In order to apply active noise control techniques into practical engineering easy, adaptive acoustical structure was proposed. As a basic theoretic research of the adaptive acoustical structure, this thesis focuses on the following three aspects.Firstly, active control of low frequency sound radiation using planar secondary source is theoretically investigated. The sound power of the primary and secondary panels is calculated, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiated sound power. Then, according to the theoretic result, the control rules of how to choose and place the planar secondary sources are given from computer simulations.Secondly, the basic principle of the flat loudspeaker is introduced briefly, then theoretical model based on sound radiation is established and mathematical expressions for calculating sound pressure and sound power are derived. Radiation directivity and sound power versus frequency are given from computer simulations and applications of panel sound sources into adaptive acoustical structure are investigated.Finally, the characteristics of the sound field are compared between the flat panel loudspeaker and the lumped parameter loudspeaker based on experimental results. It is proven that the flat panel loudspeaker can be applied in active noise control by examining sound field of the combination of the flat panel loudspeaker and the active noise control experiment.It is concluded that the flat panel loudspeaker is more suitable than the lumped parameter loudspeaker when used as the secondary sound source in active noise control.