Flat sources for active acoustic shielding based on distributed control of a vibrating plate coupled with a thin cavity

Air cavities between plates are often used to improve noise insulation by passive means, especially at high frequencies. Such configurations may suffer from resonances, such as due to the mass-air-mass resonance. Lightweight structures, which tend to be undamped, may suffer from structural resonances as well. Active methods have been suggested for improved noise insulation of plates, using piezoelectric patch actuators or inertial mass actuators. Other active methods for improved noise insulation can be based on acoustic control of the sound field in the cavity, using acoustic sources and acoustic sensors. Methods based on feedforward control of the sound radiated from such panels with air cavity usually suffer from an irregular frequency response of the actuators on the radiating panel and insufficient acoustic control authority at low frequencies. This paper presents a method to realize the combination of the air cavity and a radiating surface with a well controlled vibration distribution over the radiating surface. A specific distributed controller results in a smooth and well defined frequency response over a broad frequency range, enabling effective feedforward control of the radiated sound. Experimental results agree with numerical predictions.