ACTIVE NOISE CONTROL OF SOUND PROPAGATION IN THE DUCT

Abstract

This report presents general background information about ANC methods. Contrasts between passive and active noise control are described and circumstances under which ANC is preferable are given. An ideal filtering problem is discussed to introduce notation, properties, and analysis techniques that can be applied to adaptive transversal filters and adaptive algorithms: Steepest descent and LMS are discussed in detail. The report details the design of a closed loop feedforward adaptive noise control with LMS algorithm and the implementation of that design in real time with a DSP kit (TMS320C671 1). An experiment on a circular flow duct for active control of the acoustic transmissions produced 1/3rd octave band acoustic source at central frequencies of 50Hz, 150Hz, 400Hz and 600Hz is performed. The attenuation of sound pressure level 16dB to 20dB for open loop adaptive control system and 32dB for closed loop adaptive control system is obtained at measuring section M4