Active noise cancellation system

Details Active noise cancellation system Active noise cancellation system

1996-03-08

1999-01-19

Isen, Forester W.

Electrical audio signal processing systems and devices

Acoustical noise or sound cancellation

Adjacent ear

381 717, 381 718, 381 96, G10K 1116

Patent

active

058622349

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates in general to active noise cancellation systems, and in particular to such systems which employ a microphone proximate a listener's ear to receive essentially the same ambient noise received by the ear and a speaker for producing sound in the vicinity of the microphone to cancel the ambient noise.
Prior art as in U.S. Pat. No. 2,972,018 by Hawley et al. (1953) provide for a microphone which responds to ambient noise and a speaker which transmits an altered version of the ambient noise to provide a measure of noise cancellation in the region of the microphone. Virtually all subsequent patents of improvement incorporate some variant of this concept, but they all use microphones.
This invention takes advantage of the known fact that certain kinds of speakers (e.g. diaphragm speakers) respond to pressure waves of incoming sound (e.g. ambient noise) and produce an output signal representative of the incoming sound.
Other advantages and attributes of this invention will be readily discernable from a reading of the text hereinafter.


SUMMARY OF THE INVENTION

An object of this invention is to provide the means to implement active noise attenuation systems without the need to use a microphone.
A further object of this invention is to provide an active noise attenuation system in a which a speaker is used as a bilateral transducer, i.e. a transducer that both converts acoustic waves to corresponding electrical energy and converts electrical energy to acoustic waves.
These and other objects, which are apparent from this specification, are achieved by an improvement for at least eliminating the microphone from any ANC ("active noise control") device having at least a microphone which responds to ambient acoustic noise waves and a speaker which transmits an altered version of the ambient noise waves over a frequency range to provide a measure of noise cancellation in the region of the microphone, the improvement comprising: (a) bilateral transducer means, disposed in said region, for converting the acoustic noise waves to a corresponding first signal and for converting a second signal to corresponding acoustic waves; and (b) means for applying a transfer function to the first signal, over said frequency range, resulting in the second signal, the transfer function causing acoustic waves produced by the bilateral transducer to be generally equal in magnitude but opposite in phase to the acoustic noise waves impinging the bilateral transducer. The objects are also achieved by two embodiments of an ANC system. A first embodiment comprises: (a) a bilateral transducer means, disposed proximate a listener so as to be impinged by the same acoustic noise waves to which the listener is subjected, for converting the acoustic noise waves to a corresponding first signal and for converting a second signal to corresponding acoustic waves; and (b) means for applying a transfer function to the first signal, over a frequency range, resulting in the second signal, the transfer function causing acoustic waves produced by the bilateral transducer to be generally equal in magnitude but opposite in phase to the acoustic noise waves impinging the bilateral transducer. A second embodiment comprising: (a) bilateral transducer means, disposed proximate a listener so as to be impinged by the same acoustic noise waves to which the listener is subjected, for converting the acoustic noise waves to a corresponding first signal and for converting a sum signal to corresponding acoustic waves; (b) means for applying a transfer function to the first signal, over a frequency range, resulting in a second signal; (c) a feed forward circuit comprising: (i) acousto-electric transducer means, disposed to be impinged by the same acoustic noise waves to which the listener is subjected for converting the noise waves to a corresponding third signal, and (ii) means for applying a transfer function to the third signal resulting in a fourth signal; and (d) means for summing the second and the fourth signals to pro

REFERENCES:
patent: 4243839 (1981-01-01), Takahashi et al.
patent: 4712247 (1987-12-01), Swarte
patent: 4833719 (1989-05-01), Carme et al.
patent: 4985925 (1991-01-01), Langberg et al.
patent: 5267321 (1993-11-01), Langberg

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