Study on the Howling Canceler in Active Noise Control : Two Microphone Delay System

An active noise control technique for prevention of howling is studied in this paper. A 2-Microphone system is often employed in a long-sized duct, where the propagation wave is the main component. However, in a short-sized duct, the reflected waves must be considered. In this case, the authors introduced the acoustic condition that the component of the reflected wave should be absorbed at the end opposite the opening end. The authors called this system the 2-Microphone delay system. The acoustic property of the duct for the 2-Microphone delay system was examined. The effect of this active noise control system with a howling canceler was compared with a 1-Microphone system. Their characteristics were examined by comparing theoretical results with the experimental results. The features of the individual systems have been determined. It was found that the digital filter in the 2-Microphone delay system implements the control filter characteristics except the frequencies determined by the distance between two microphones. On the other hand, the implementation of the 1-Microphone system was poor.