Abstract
This paper describes an active noise control technique to suppress the transmitted sound from a movable louver that is attached to a ventilation aperture and machinery opening. In this experimental study, proposed ANC (Active Noise Control) system is independent parallel control system using two IMC (Internal Model Control) feedback ANC systems. Each system is controlled using filtered-X LMS algorithm to minimize sound pressure at error microphone. One of them, louver-ANC system which secondary noise source is set at each bottom side of the louver vane. An opening of each movable louver vane is one-dimensional space similarly a duct. Transmitted sound is attenuated in this area which error microphone was set on outside near louver opening. The other one is slit-ANC system that is installed on an opening of machinery wall. The slit-ANC system is combined a slit resonator with active noise control. The slit resonator with ventilation aperture composed of thin air layer expanded with very short wall width is useful to reduce leakage noise at machinery wall. The thin air layer acts an acoustic resistance, inertance and capacitance. The secondary noise source oscillates the air layer with appropriate amplitudes and phases. The error microphone is located same position in case of the louver-ANC system. The rectangular slit resonator is designed to reduce resonant frequencies of an enclosure box in this experiment. Noise reduction is visualized by sound intensity measurement system, and sound power is calculated by distribution of sound intensity. The experimental results show that noise reduction is obtained from 5 dB to 13 dB of sound power in sound field on this proposed ANC system. And it is expected that the transmission loss of movable louver will be able to improve by using independent parallel control system of louver-ANC and slit-ANC.
