Active intensity control for the reduction of radiated duct noise

Abstract

Mean intensity based active control for the cancellation of radiated noise out of the duct exit is studied. The active intensity control strategy is derived based on the relation of the exterior sound field radiated out of the duct termination and the interior sound field of the duct. One of the characteristics of this control strategy is that the maximum possible control performance can be maintained regardless of the sensor location, compared with the conventional local pressure control methods at either interior downstream or exterior field positions. This is a simple consequence of the active intensity at the interior downstream being not space-dependent as long as it is plane wave. A time-domain adaptive filtering method for the active intensity control is also suggested and experimental results for an open ended duct based on the adaptive filtering method are presented. For the purpose of practical comparison, experimental results for conventional sound pressure control based on the well known filtered-x LMS algorithm are also presented. The experimental results show the potential of the active intensity control strategy for reducing the emitted noise out of the duct exit. (C) 1997 Academic Press Limited.