An Experiment on Optimization of Active Noise Control on a Three-Dimensional Extended Radiator

Abstract

In this experiment, a 10.6 dB reduction in the total radiated sound power for an extended radiator was achieved via active control through optimization of active sources. An acoustic boundary element program was used to determine the magnitude and phase of the active sources which minimized the total radiated sound power. This paper details the experimental verification of the numerically predicted active source strengths using a box-shaped acoustic radiator. The top and bottom of the radiator were thin steel plates which were driven in one of their structural modes by an electromagnetic shaker. The four corners of the top plate were removed to accommodate baffled loudspeakers, representing the active sources. To provide precise control of the experiment, the driving signals to the shakers and loudspeakers were generated and monitored by a control computer. The experimental results agreed closely with the analytical prediction, confirming that the optimum reduction had been achieved for the primary and active source configuration. The measured sound pressure reductions in the acoustic field of the radiator ranged from 8 dB to 19 dB for the 1,1 structural mode of the plates.