Aim To study a method realizing noise control for a physical model of progressive wave in a duct. Methods A mathematical model was constructed and a transfer function of the adaptive system for noise control was also worked out; moreover, the effects of some algorithms such as RLS,LMS and LSL on noise control were analyzed and compared. Results Without the feedback of sound, the mean noise reduce value(MNRV) of 27 5 dB for broadband noise from 0 to 500?Hz in frequency were achieved. When acoustic feedback took place and an air stream loudspeaker was used, the MNRV was only about 4 9?dB. But if the loudspeaker had a plain frequency feature, MNRV was improved by 10 2?dB. Conclusion The technique is applied to ruducing the noise from engines' exhausted gas pipes. It is, in principle, used for noise cancelling in a closed three dimensional space.
On the basis of the theory of adaptive active noise control(AANC) in a duct, this article discusses the algorithms of the adaptive control, compares the algorithm characteristics using LMS, RLS and LSL algorithms in the adaptive filter in the AANC system, derives the recursive formulas of LMS algorithm. and obtains the LMS algorithm in computer simulation using FIR and IIR filters in AANC system. By means of simulation, we compare the attenuation levels with various input signals in AANC system and discuss the effects of step factor, order of filters and sound delay on the algorithm's convergence rate and attenuation level.We also discuss the attenuation levels with sound feedback using are and IIR filters in AANC system.
