Acoustic Power Minimization by Active Noise and Vibration Control. On the Acoustic Radiation Impedance and Zero Control Power Output.

Abstract

This paper deals with the acoustic power minimization problem from the viewpoint of an active noise and vibration control. This paper places a particular emphasis on the phenomenon in which the acoustic power output of the control source under optimal conditions always becomes zero. It is found that the acoustic radiation impedance at and around the control point source becomes reactive under the optimal condition, and hence power output of the control source results in null. It is also shown that the reactive acoustic intensity dominates even in the vicinity of the primary source in order to impede the sound radiation from its source. In active vibration control, the power flow in terms of a control force, applied directly to a vibrating structure in an effort to attenuate the radiated sound is found to be zero. Under the optimal condition for minimizing the total acoustic radiation power, the effect of the reactive sound field outweighs that of the active sound field significantly over the vibrating plate.