Research And Design Of Active Noise Control System In Enclosure

Noise is generated by the vibration of objects,which always disturbs human beings.In the field of national defense aviation,some cabin noises directly affect the operating environment of the staff,and noise-induced structural vibration may also affect the safety and service life of the equipment.Traditional noise reduction methods have poor effect on low-frequency noise suppression,and active noise control(ANC)techniques have received wide attention due to its excellent low-frequency noise reduction performance.This paper studies and improves the ANC system from three aspects of theory,system construction and experimental verification.The main work is as follows:(1)In this paper,the structure,theories and filtered-x LMS(Fx LMS)algorithm of the classical multi-channel ANC system were introduced.Aiming at the dual-channel ANC system,a new variable step-size Fx LMS(VSS-Fx LMS)algorithm was derived and simulated.The simulation results showed that the convergence speed and steady-state performance of the new algorithm were better than the traditional one,especially when the initial step size factor was relatively large or small.(2)A multi-channel ANC system controller was designed and manufactured.In hardware,the peripheral circuits,which include a noise signal acquisition module and a secondary noise output module,were designed based on the TMS320C6747 core board.In software,the underlying drivers of the controller were implemented,mainly including the multi-channel audio buffer serial port Mc ASP,SPI communication protocol,DMA transmission.The dual-channel classic algorithm and the dual-channel VSS-Fx LMS algorithm were transplanted on the above platform respectively.(3)Experiments were performed on the classic dual-channel ANC system and single-channel ANC system respectively.Conclusions were easily obtained from the exprimental results that the former system was more effective than the latter one,in terms of noise reduction range,amount and flatness.(4)Three different initial step-size factor were conducted in the comparative experiments of classic dual-channel ANC system and dual-channel VSS-Fx LMS system.The experimental results showed that the new algorithm can balance the convergence speed and steady-state performance,which is more efficient when the initial step-size factor value is relatively large or small.The experiemental results are consistent with the simulation.(5)The above experimental results contained a lot of high frequency noises.The causes of this phenomenon were analysized and the dual-channel VSS-Fx LMS algorithm was improved.The improved system can effectively reduce high frequency components and increase the noise reduction amount by 1-3d B in the condition that initial step-size factor was large or moderate.However,when the initial step-size factor was small,the system fails.The performance of the improved system depended on the reasonable adjustment of the parameters.