Electrical audio signal processing systems and devices – Hearing protectors – electrical
Patent
1985-04-03
1987-03-31
Dwyer, James L.
Electrical audio signal processing systems and devices
Hearing protectors, electrical
381 94, G01K 1116, A61F 1102
Patent
active
046548718
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improved arrangement for the active cancellation of repetitive noise at the location of the ears of a person operating in an environment where there is at least a substantial background of such noise. The method and apparatus of which this invention relates has the advantage that because the cancellation only affects noise synchronised to the source (or sources) of the background noise, the bulk of the low frequency spectrum which is not synchronised remains unaffected, thus allowing good speech intelligibility, or improved audibility of sounds unsynchronised to the noise source, in the presence of low frequency machinery-induced noise. Thus warnings and sounds not related to the machinery will be substantially unaffected and their audibility can thus be enhanced by the method and apparatus described herein.
BACKGROUND ART
British Patent Specification No. 1577322 discloses a method of reducing the amplitude of sound variations received at a selected location from a source of recurring noise which employs a waveform generator producing a synthesised waveform capable of being used to generate a cancelling sound in the location for the noise entering that location and uses a triggering signal, derived from the source, to accurately relate the generation of the cancelling sound to the noise it is wished to cancel. This prior specification (the entire disclosure of which is herein incorporated by reference) forms the basis for the present invention.
It is also known from Wheeler and Halliday's published representation (entitled "An active noise reduction system for aircrew helmets--flight trials in strike aircraft") presented at Birkbeck College, London, on Feb. 16, 1981, to mount an active noise reduction system in a passive ear defender to cancel the acoustic noise field detected inside an ear defender. However this known arrangement is incapable of distinguishing between components of the noise field and is thus of limited use and is not effective at all for improving the audibility of random signals appearing in a high background of repetitive noise signals.
BRIEF STATEMENTS OF INVENTION
According to one aspect of the present invention there is provided a method for discriminating between a desired signal fed to an ear of a hearer and an interfering background noise in the hearer's ear, derived from a source of repetitive noise signals, which method comprises feeding a cancelling waveform to an acoustic transducer adjacent to the hearer's ear, and adjusting the cancelling waveform to optimise the efficiency of cancellation obtained in the hearer's ear, which method is characterised in that the noise-cancelling waveform is synchronised to the source of repetitive noise to selectively cancel that component of the sound reaching the hearer's ear which is derived from the said source.
In one embodiment, an open-backed headset is employed so that the repetitive background noise and the signal which the hearer wishes to hear are both airborne to the hearer's ear and the background noise is more strongly attenuated than the signal by an acoustic transducer carried in the headset. Normally of course separate acoustic transducers will be provided for each ear and suitably each transducer is fed with its own cancelling waveform derived from a separate waveform generator. The two generators can, however, receive common synchronising trigger signals from the noise source.
In a second embodiment, a closed-back headset is employed, the required signal being fed electrically to an acoustic transducer adjacent to the ear. Some background noise from the source of repetitive noise (particularly the lower frequency components) leaks around the seal between the headset and the wearer's head, but this can be selectively cancelled by feeding the appropriate noise cancelling waveform to the transducer with the required signal.
In a third embodiment, a headset is again employed, but here the noise signal is arriving with the required signal to the acoustic transducer in the heads
REFERENCES:
patent: 2972018 (1969-02-01), Hawley et al.
Bramer Terrence P. C.
Chaplin George B. B.
Smith Roderick A.
Dwyer James L.
Sound Attenuators Limited
LandOfFree
Method and apparatus for reducing repetitive noise entering the does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for reducing repetitive noise entering the , we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for reducing repetitive noise entering the will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2218318