Research On Active Noise Reduction System In Confined Space

Noise pollution is ubiquitous in daily life,but it is easy to be ignored.The lowfrequency component of noise has the characteristics of long wavelength and low frequency,which is not easy to be detected,but it will cause clinical reactions such as dizziness and vomiting.At the same time,the vibration excitation of low-frequency noise will reduce the accuracy of production equipment then making it difficult to ensure quality.The traditional method to reduce noise is to use sound absorbing materials to establish a barrier during noise propagation,but this method has little effect on low frequency noise.Adopting active noise control can make up for the shortcomings of traditional methods.It is a new noise reduction method based on digital signal processing technology and has a good noise reduction effect for low-frequency noise signals.Active noise reduction system has become the main research direction of noise control because of its noise adaptive ability,convenient installation,and suitable for different environments.When the noise control system is running,the electroacoustic devices are responsible for the acquisition and playback of the noise signal,and the signal distortion directly affects the noise reduction performance of the control system.Therefore,it is significant to study the effect of frequency response characteristics of electroacoustic devices on noise control.In this paper,the noise field in a confined environment is taken as the research object.Based on the study of acoustic theory,the feasibility of active noise control is verified by combining the principle of acoustic interference.The principle of LMS algorithm is studied.Considering the noise delay problem in the actual environment,the offset path is introduced into the LMS algorithm and generalized as the Fx LMS algorithm.The off-line modeling method was used to identify the system characteristics of the offset path to solve the signal attenuation and phase misalignment caused by the acoustic delay problem.A noise control experiments are conducted on the mixed white noise signals to analyze the noise reduction performance of Fx LMS algorithm.In order to study the influence of the frequency response characteristics of the electroacoustic device on the modeling of secondary path during ANC system simulation,a new secondary path model analysis method was proposed.The frequency response curve of the electroacoustic device was simulated by using a lateral FIR filter.And the Fx LMS(Filtered-x Least Mean Square)algorithm was taken as an example to study the effect of the frequency response of electroacoustic devices on the noise reduction of the ANC system.The simulation results show that steep frequency response curve of the electroacoustic device will attenuate the amplitude of input signal,resulting in a phenomenon of amplitude mismatch,which makes the actual noise reduction of the control system much smaller than the ideal electroacoustic device model.The effects of electroacoustic devices on the noise reduction system are analyzed by the denoising effects of different situations.Aiming at the problem that the frequency response of electroacoustic devices affect the noise reduction of the system,the active noise reduction system structure was improved by combining an inverse filtering algorithm based on minimum phase decomposition.The frequency response curve of the mono system was modeled by using the inverse filter algorithm.Cascading the obtained inverse filter with the original system can reduce the degree of curve fluctuation and achieve a flat output.The simulation results show that the control system combined with the inverse filter algorithm has a better noise reduction effect on the noise signal.At the same time,by reducing the order of the inverse filter,the system can achieve the same compensation effect with lower order.