Development of Wide-Band Active Noise Control System for One-Dimensional Acoustic Duct Using Progressive Wave as Control Signals. 1st Report. Trial Construction of Control System and General Considerations of Noise Reduction Performance.

Abstract

A new active noise control system for air-conditioning ducts has been presented, together with experimental results. The control system detects the progressive wave component of fluid-borne vibration and then controls the second source feed-forwardly using this detected signal so as to eliminate the progressive wave in its downstream duct by producing cancelling (anti-phase) fluid vibration. The key points of the design of the active noise control system, in which a transfer function-based method is used, are the following : (1) satisfactory noise reduction performance achieved by matching the transfer function of the controller (specifically, the signal processor for control) with the desired (target) characteristics as much as possible, and (2) prevention of howling by increasing the degree of stability. It has been confirmed by both theoretical analysis and tests carried out on a small model apparatus that, when the present control system was operated, pressure pulsation(noise)in a duct down stream of the second source was reduced by aroud 1/10(20 dB) of that in the case where the control system was not operated for almost all harmonics of 40 Hz to 600 Hz, and that the present system had a far higher degree of stability than that of Lueg's system.