Study On Automotive Interior Active Noise Control Method Based On Sound Quality Improvement

Based on destructive interference of two sound waves, active noise control (ANC) is aforceful tool to be used to decline vehicle inner low frequence noise. And improvement ofsound quality is the intent of vehcle interior noise control. Conventional ANC adaptiveLMS algorithm and post-masking effort of human hearing were combined to developPmLMS (Post-masking LMS) algorithm in this paper, it intends to get lower loudnessvalue than LMS algorithm about canceling vehicle interior noise, at the same time,improve sound quality of that.Because of that loudness impacts sound quality in vehicle cabin greater than the otherobjective sound quality parameters like sharpness, loudness was selected as the index ofsound quality evaluation of automotive inner noise in this paper at first. Afterwards,automobile interior noises under uniform speed were measured and then filtered to gainsome samples as objects of ANC. After studied conventional LMS algorithm with it’sconvergence and accomplished it’s Matlab program, this paper studied post-masking effortwith it’s application, and then developed a new LMS algorithm—PmLMS algorithm, andthen implements simulation of automobile interior ANC with LMS algorithm and the newalgorithm in Matlab software. Results suggest that PmLMS algorithm get lower values ofloudness than conventional LMS algorithm with conditions of same iteration step size,fixed filter order and same control objects.At last, these two active filter algorithms with variable iteration steps were simulatedand analyzed, there are four same points of property:1, linear SPL (sound press level) andloudness value of simulation result of every measureing noise all decrease with increase insteps until the optimum step size, respectively, then shock phenomenon would emerge, unstable state and non-convergence would appear with longer and increasing steps. Higherthe automotive speed, narrower the range of appropriate step;2, reduced rates of the linearSPL and loudness value are slower with increasing steps;3, higher the speed, larger thevalue of RRAL (Relatively Reduced Amount of Loudness) under same iteration step, thatis to say stronger ANC capacity. Enhance rates of ANC capability under high speedcondition are higher than those of low with increasing step sizes;4, enhance rates alldecrease with increase in steps until the optimum step size, respectively. Above four pointsof property show that new PmLMS algorithm ensures the continuity of conventional LMSalgorithm.However, linear SPL and loudness value of measureing noises eliminated by PmLMSalgorithm with variable steps were lower than those of LMS, PmLMS algorithm is betterthan conventional LMS algorithm considering decrease of loudness, improvement of soundquality and raising convenient feeling by passenger. This advantage bases on shortenedrange of appropriate step.In practical application of LMS algorithm and PmLMS algorithm, there would be amatch between step size and vehicle speed in order to prevent the shock phenomenon andlead to better effect of noise elimination.