Active noise supressors and methods for use in the ear canal
Goodwin, S. (1998). Active noise supressors and methods for use in the ear canal. (U.S. Patent No. 5740258). http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=5740258
A noise suppressor includes an input transducer and an output transducer adapted to be located in an ear canal. A housing is provided to support the transducers in the ear canal, and the housing provides an acoustically unobstructed passage from the entrance of the ear canal to the ear drum. The input transducer generates electrical signals in response to sound pressure waves entering the ear canal, and a portion of the electrical signal is processed to generate an inverse noise signal which is applied to the output transducer. Accordingly, the output transducer produces inverse noise pressure waves in order to reduce an undesired noise portion of the sound pressure waves reaching the ear drum. The sound pressure waves also reach the ear drum without significant alteration.