Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Adjacent ear
Patent
1983-10-12
1984-12-18
Rubinson, Gene Z.
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Adjacent ear
381 94, G10K 1116, H04R 128
Patent
active
044894414
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an improved method and apparatus for the nulling of a primary vibration (e.g. noise in a gas) by the "active" method, i.e. the generation of a cancelling vibration (e.g. anti-noise) which coacts with the primary vibration (e.g. noise) to at least partly null it in a selected location.
BACKGROUND ART
Various proposals have been made for generation of effective "anti-noise" signals and reference may be made to the specifications of U.S. Pat. Nos. 4122303 and 4153815.
This invention is concerned with improvements in a simple system for active noise cancellation which operates in the frequency domain and is sometimes referred to as the "virtual earth" system. This system is described for instance in the specification of U.S. Pat. No. 2983790 (Olson). The "virtual earth" system can be used to create a quiet zone in the vicinity of a microphone disposed in a sound field, by locating a loudspeaker closely adjacent to the microphone (e.g. some 10 cms away) and coupling the microphone and loudspeaker into a loop circuit producing an overall gain greater than unity and a 180.degree. phase reversal. This known "virtual earth" system operates by continually controlling the output from the loudspeaker so that it nulls the sound field at the microphone.
The known arrangement is shown in the first figure of the accompanying drawings to be discussed hereafter from the discussion of that figure, the limitations of the known system will become evident.
The present invention seeks to increase the distance over which a "virtual earth" system is effective without reducing the frequency range over which the "virtual earth" system can operate.
DISCLOSURE OF INVENTION
According to one aspect of the invention a method of attenuating, in a desired location, a vibration entering that location from a primary source of vibration which method comprises injecting into that location a nulling vibration of such waveform and amplitude that it will at least partially cancel the effect of the primary vibration in the desired location, the waveform being generated in an amplifying/phaseshifting feedback loop linking a vibration-sensing transducer and a closely proximate vibration-transmitting transducer, is characterised in that the waveform generated in the loop is amplified and used to generate a secondary vibration which is fed into the location to produce a null at a position remote from the vibration-sensing transducer of the loop.
The known "virtual earth" system uses the feedback loop as an automatic waveform generator which in a simple manner produces the correct secondary vibration for producing the "virtual earth" at the location of the vibration-sensing transducer.
By this invention it has been appreciated that the role of the feedback loop to produce the correct waveform, can be separated from the role of the loop to produce the correct amplitude. Thus by using the loop in its waveform shaping role and "over amplifying" the waveform signal, it is possible to move the "virtual earth" into the far field of the vibration-transmitting transducer without bringing the frequency at which the loop will oscillate into the working range of an active attenuation system (e.g. up to a few hundred Hertz).
The vibration-transmitting transducer used in the feedback loop can be used to produce the secondary vibration generating the "virtual earth" in the said location or the waveform fed to this transducer can be amplified and fed to a similar adjacent vibration-transmitting transducer, whose output is projected into the location.
According to a further aspect of the invention, apparatus for nulling a primary vibration in a selected location by using a specially generated secondary vibration fed to the location, which apparatus comprises a vibration-receiving transducer sensing the primary vibration, a vibration-transmitting transducer located adjacent to the vibration-receiving transducer and connected therewith in a phase-inverting feedback loop and is characterised in that a second vibration-rece
REFERENCES:
patent: 2983790 (1961-05-01), Olson
patent: 3826870 (1974-07-01), Wurm et al.
patent: 4044203 (1977-08-01), Swinbanks
patent: 4122303 (1978-10-01), Chaplin et al.
patent: 4153815 (1979-05-01), Chaplin et al.
Dwyer James L.
Rubinson Gene Z.
Sound Attenuators Limited
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