Experiments on the active control of sound radiation using a volume velocity sensor

The reduction of sound radiation from vibrating structures is an important problem in acoustics. The sound power radiated from a structure can be reduced by altering the dynamic properties of the structure or by isolating the structure from the source of excitation. This is generally termed passive control. In some applications, notably aircraft, the weight penalty imposed by passive control techniques can be prohibitively large, especially at low frequencies. In these applications active control systems which use secondary control actuators can be used as an alternative technique for reducing the sound power radiation.2''1 It has been shown that the volume velocity of a surface is responsible for the majority of the sound power radiation at low frequencies.3 It has therefore been suggested that the cancellation of volume velocity is an appropriate strategy for reducing the sound power radiation from vibrating surfaces.7 In order to actively cancel the volume velocity of a surface an accurate measure of the volume velocity is required. Designs for volume velocity sensors have been suggested using piezoelectric material etched or cut into specific shapes.4'6"° In the experiments described in this paper such a sensor is tested and used to control the sound power radiation from a rectangular aluminium panel.