Active attenuation of noise in a closed structure

A system for the attenuation of sound waves produced in a closed structure having walls, an interior and an exterior surface by at least one source of sound, said source sound waves producing a plurality of areas of high acoustic pressure and low pressure within said interior of said closed structure, and at least a portion of said source sound waves impinging against said exterior surface of said closed structure in a pattern and inducing vibration of said walls, said system comprising:

• first input sensing means disposed adjacent to an area of high acoustic pressure within said interior, and second input sensing means disposed adjacent said source of sound, said first and second input sensing means being operable to sense said source sound waves and produce electrical signals representing the amplitude and phase characteristics of said source sound sensed thereby;
• first cancelling means disposed within said closed structure and being spaced from said first input sensing means, and second cancelling means disposed adjacent said closed structure wall and being spaced from said second input sensing means, said first and second cancelling means being operable to generate cancelling sound waves of corresponding amplitude but 180.degree. out-of-phase with said source sound waves for combination therewith;
• first error sensing means disposed adjacent to a high acoustic pressure area within said closed structure and being spaced from said first cancelling means, and second error sensing means disposed within said closed structure and being spaced from said second cancelling means, said first and second error sensing means being operable to sense the acoustic summation of said source sound waves and cancelling sound waves and produce electrical signals representing the amplitude and phase characteristics of said combination of said source sound waves and cancelling sound waves;
• and
• first electronic controller means connected with said first input sensing means, said first cancelling means and said first error sensing means, said first electronic controller means being operable to process said electrical signals from said first input sensing means, produce outputs for driving said first cancelling means to produce said cancelling sound waves, and to adjust said outputs based on said electrical signals from said first error sensing means for the production of revised outputs for driving said cancelling means;
• and
• second electronic controller means connected with said second input means, said second cancelling means and said second error sensing means, said second electronic controller means being operable to process said electrical signals from said second input sensing means, produce outputs for driving said second cancelling means to produce said cancelling sound waves, and to adjust said outputs based on said electrical signals from said second error sensing means for the production of revised outputs for driving said cancelling means.