Actuators positioning for multichannel active control system in circular ducts

In the particular case of multichannel control, the acoustic power limit of loudspeakers may be an important restriction for active control application when the noise levels are very high. The goal of this paper is to present the different parameters that allow to minimize the power used by the control sources for a multichannel active control system in a circular duct. An experimental study of the longitudinal distribution pressure field for the particular case of higher order modes, as well as some experimentations with active control for different geometric conditions have been done to analyze this problem. The results of these experimentations have allowed us to understand that the most influential phenomenon that determines the control sources optimum position are the reflection from ducts closed end. With this result in mind, a simple and efficient methodology of positioning has been developed. The efficiency of this positioning method has been proved from experimental tests.