Study on the Effect of Active Noise Control Using Howling Canceller. Comparison of 1-Microphone System to 2-Microphone Delay System.
Seiichirou Suzuki, Takurou Hayashi · TRANSACTIONS OF THE JAPAN SOCIETY OF MECHANICAL ENGINEERS Series C · 1993
Howling occurs because the noise control signal from a secondary source is detected. A 2-Microphone system utilizing a time delay corresponding to the distance between the two microphones is often used as a howling canceller in long ducts where unidirectional acoustic wave is the main component. In this system, the delayed signal fed into a microphone is subtracted from another microphone signal. In short ducts, many reflected waves exist due to the difference in acoustical impedance at the ends of the duct. The authors show that in such cases it is necessary for the reflected waves opposite the opening end to be absorbed. For this purpose, the authors propose a system which they call the 2-Microphone delay system. In this paper, the noise reduction effect radiated from the noise speaker of the duct is examined. A noise control digital filter characteristic of the 2-Microphone delay system is examined theoretically and experimentally from the viewpoint of the digital filter causality. The noise control digital filter characteristic is compared with the normal 1-Microphone system without a howling conceller.