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Noise cancellation

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US3826870A
US3826870A US2155470A US3826870A US 3826870 A US3826870 A US 3826870A US 2155470 A US2155470 A US 2155470A US 3826870 A US3826870 A US 3826870A
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sound
noise
waves
channel
member
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R Wurm
A Bergson
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QUEST ELECTRONICS CORP
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QUEST ELECTRONICS CORP
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16LPIPES; JOINTS OR FITTINGS FOR PIPES; SUPPORTS FOR PIPES, CABLES OR PROTECTIVE TUBING; MEANS FOR THERMAL INSULATION IN GENERAL
    • F16L55/00Devices or appurtenances for use in, or in connection with, pipes or pipe systems
    • F16L55/02Energy absorbers; Noise absorbers
    • F16L55/033Noise absorbers
    • F16L55/0333Noise absorbers by means of an active system
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16Methods or devices for protecting against, or damping of, acoustic waves, e.g. sound
    • G10K11/175Methods or devices for protecting against, or damping of, acoustic waves, e.g. sound using interference effects; Masking sound
    • G10K11/178Methods or devices for protecting against, or damping of, acoustic waves, e.g. sound using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10Applications
    • G10K2210/128Vehicles
    • G10K2210/1282Automobiles
    • G10K2210/12822Exhaust pipes or mufflers
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30Means
    • G10K2210/301Computational
    • G10K2210/3011Single acoustic input
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30Means
    • G10K2210/301Computational
    • G10K2210/3013Analogue, i.e. using analogue computers or circuits
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10KSOUND-PRODUCING DEVICES; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K2210/00Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30Means
    • G10K2210/321Physical
    • G10K2210/3219Geometry of the configuration

Abstract

A pipe for an engine exhaust is joined with a cancellation tube in a V-joint and beyond this joint a single pipe portion extends to an exhaust opening. The cancellation tube provides a shunt path for sound waves produced by a sound transducer disposed at the outside end of the cancellation tube. The sound transducer is driven by an amplifier and phase inverting network which in turn responds to a sensor transducer in the first pipe. This transducer establishes a signal in accordance with the noise in the first pipe and the sound transducer thus produces sound waves corresponding to and about 180* out of phase with the engine noise. At the V-joint, the noise of the engine exhaust is largely cancelled by the waves in the cancellation tube.

Description

United States Patent [191 Wurm et a1.

1111 3,826,870 1 July 30, 1974 [541 NOISECANCELLATION 21 Appl. No.: 21,554

[52] US. Cl 179/1 P, 181/33 L, 181/33 C [51] Int. Cl H04r 1/28 [58] Field of Search 179/1 D, 1 F, 1 FS, 1 P,

[56] References Cited UNITED STATES PATENTS 6/1936 Lucg 179/1 P 3,071,752 1/1963 Strasberg 179/1 P 3,396,812 8/1968 Wilcox et al 181/48 FOREIGN PATENTS OR APPLlCATlONS 132,227 9/1932 Austria 181/48 Noise Source Changer F Primary Examiner-William C. Cooper Attorney, Agent, or Firm-Andrus, Sceales, Starke 8L Sawall 5 7] ABSTRACT A pipe for an engine exhaust is joined with a cancellation tube in a V-joint and beyond this joint a single pipe portion extends to an exhaust opening. The cancellation tube provides a shunt path for sound waves produced by a sound transducer disposed at the outside end of the cancellation tube. The sound transducer is driven by an amplifier and phase inverting network which in turn responds to a sensor transducer in the first pipe. This transducer establishes a signal in accordance with the noise in the first pipe and the sound transducer thus produces sound waves corresponding to and about 180 out of phase with the engine noise. At the V-joint, the noise of the engine exhaust is largely cancelled by the waves in the cancellation tube.

5 Claims, 2 Drawing Figures PATENIE JULBomM Changer INVENTORS Robert J. Wurm y Arnold A. Bergson %WZAALQ Attorneys NOISE CANCELLATION BACKGROUND OF THE INVENTION This invention relates to active noise cancellation and more particularly to active noise cancellation in sound transmission channels that carry sound waves from a noise source.

Various noise sources transmit sound through confined sound transmission channels. For instance, combustion engines cause pulsating, high volume noise which is most noticeably emitted through their exhaust channels. Previously, noise suppression for this exhaust has involved passive devices such as mufflers, that are effective silencers only at the expense of obstructing the free flow of the exhaust, resulting in undesirable back pressure on the engine. Other sound transmission channels present similar difficulties in noise reduction. It has been recognized theoretically that active noise reduction concepts could be employed to cancel noise waves. However, the prior art has not revealed a successful active device for use in confined channels.

For example, noise is very often random in character, and for effective cancellation, the active device has to nearly duplicate the noise waves. In the prior art, active noise cancellation has been provided only for single or regular tones, and therefore is not useful for such applications as engine exhaust noise cancellation. As well, prior art devices are dependent on the noise source, requiring tuning to the source in order to duplicate the waves. Further problems are experienced in attempting to obtain a mechanical arrangement of the active device in order to provide cancelling waves which are in the same wave plane as the noise waves. Without this matching of the wave planes, cancellation occurs only at points, or only for a small part of the noise waves.

These and other problems in the art have not previously been solved. The theory has not developed into successful practice.

SUMMARY OF THE INVENTION The invention is directed to an active noise cancellation concept which is successfully employed in confined sound transmission channels and even with such severe noise sources as combustion engine exhaust systems. Other uses and advantages of the invention will be apparent from the drawings and description.

The practice of the invention provides effective noise cancellation in any confined noise channel, such as pipes, solid bars, and the like, regardless of the noise source and without obstructing the use of the channel. The noise source is at one end of a first transmission channel so that sound waves are generally confined within the channel. A second transmission-channel, or a cancellation channel, is joined to the first at a joint.

Cancelling sound waves are provided in the cancellation channel, and are channeled to the joint. At the joint, the cancelling waves are generally oppositely out of phase with, but effectively in the same plane as the noise waves in the first channel. The amplitudes and shape of the noise waves and cancelling waves are also similar, so that the two largely cancel beyond the joint.

To provide the cancelling waves, a sensor transducer is disposed at a predetermined position on the first channel. Being in communication with the pressure pulses which'comprise the noise in the channel, the sensor transducer establishes a corresponding signal to drive a driver transducer that is disposed on the cancellation channel at a predetermined position such that the distance between the sensor and the joint is related to the distance between the driver and the joint, and the sensed sound wave and the cancelling wave meet at the joint. Phase inversion is provided for the sensor signal to cause the cancellation wave to be generally oppositely phased from the noise wave at the joint.

This structure operates in accordance with the invention to provide effective noise cancellation, which works regardless of the noise source, is effective for practically any noise frequency or complexity, and avoids obstruction of the use of the sound transmission channel.

The sensor is positioned on the first channel so as to minimize feedback from the cancellation wave, which otherwise could cause instability in the system. This feedback will also be effected by the angle of the joint, and the optimum form of the invention, as limited by practical considerations of design, would be to have a relatively small angle inclined toward the noise source; although, a less perfect practice of the invention could be accomplished at any angle for channels whose thickness are small relative to the wave lengths involved.

The drawings illustrate the best mode presently contemplated by the inventor for carrying out the invention.

In the drawings:

FIG. 1 is a perspective view of an example of the invention with parts shown diagrammatically; and

FIG. 2 is a diagrammatic illustration of the invention.

DESCRIPTION In the drawings, a noise source 1 is diagrammatically shown as a four cylinder combustion engine in FIG. 1. The engine has four exhaust ports which emit exhaust into a manifold 2 connected to an exhaust pipe 3. Pipe 3 extends to a V-joint 4 where it is interconnected with a cancellation tube 5 in a V configuration. Added to the V-joint is a rear exhaust pipe 6, to add a bottom leg to the V-joint. Exhaust from source 1 passes through pipes 3 and 6 and out an exhaust opening 7 in the latter.

Cancellation tube 5 and exhaust pipe 3 are shown intersecting at a small angle, of the order of 30 or less for optimum operation in this example, and both are preferably at an angle relative to rear pipe 6. More complete cancellation of the noise will result at these small angles. But good cancellation can occur with any angle at the joint, if the diameter of pipe 3 is considerably less than the noise wave length. In that case, the pressure waves will be generally oppositely phased across the joint.

To produce cancelling sound waves in cancellation tube 5, an active system 8 couples to the exhaust pipe and cancellation tube. Included in this system is a sensor 9, which is a pressure responsive transducer with a diaphragm 10 in communication with the inside of pipe 3 through a hole 11. A seal 12 is disposed between the body of sensor 9 and pipe 3 to avoid leakage of exhaust from hole 11 into the atmosphere.

Sensor 9 may be a standard microphone for producing an electrical signal of a frequency corresponding to the noise waves of the exhaust at the position of sensor 9 and of an amplitude proportional to such noise waves. This signal is supplied via leads 13 to a phase changer network 14 and "from there to an amplifier 15. Network 14 and amplifier 15 are individually known and network 14 has an active network which causes phase shift in the signal so as to be opposed to the amplitude of the sensor signal. Optimum phase shift would be 180.

Amplifier l5 drives a driver transducer 16 to create and propagate cancelling pressure waves through cancelling tube 5. Driver 16 may also be a conventional device and is shown attached over'the outer end of the tube to couple the output of driver 16 to the cavity and close the end of the tube. in this embodiment, the driver should be a high intensity transducer to match the noise source.

The components of active system 8 drive driver 16 to produce sound waves of the same amplitude and shape as the noise picked up by sensor 9. These components are interdependent parameters which, by testing, may be chosen in accordance with the particular devices employed. The distance between sensor 9 and joint 4, or the intersection point of the two wave planes, and the distance between that point and driver 16 is another important parameter. With the 180 phase shift and with the same transmission media, these distances can be nearly equal. The intersecting waves are then out of phase after having traveled through the same distance. The phase changer network could include a suitable delay timer, not shown, so that the sensor could be moved closer to the noise source. The delay would account for the greater distance of travel for a wave from the-sensor to the joint. Except where the wave lengths are very short, such as one-fourth the length of tube 3, slight variations in these distances will not unduly hamper noise cancellation. However, if sensor 9 is too far forward of driver 16, the cancellation can be effective only with more complex and exact phase changer networks, and the noise can be cancelled only if the noise waves are predictable.

The angle of intersection of the waves is a less important factor for effective noise cancellation. Wave pulses 17 are illustrated in FIG. 2 to demonstrate this. Where the pulses from the source and from the cancellation are as nearly in the same plane as practicable when they intersect, most effective and full cancellation will occur at joint 4. With usual wave lengths in engine exhaust noise, however, effective pressure wave cancellation will occur across the full diameter of the joint even where the angle of intersection is 90 or more. For this reason, the angle between the axes of pipe 3 and cancellation tube 5 should be made as small as practical, but the matter is not critical unless the pipe diameter is large compared to noise wave length.

Feedback from the joint to sensor 9 will also have to be considered in deciding the exact arrangement of the sensor relative to the joint. The sensor should be, in effect, shielded from feedback of the cancellation waves for optimum stability. The arrangement of the sensor is best determined by trial and error testing with a particular system, and the drawings show a simple example of a successful arrangement.

The invention thus may be employed to effectively cancel noise in a tubular channel such as an exhaust pipe. The concept may be employed in any confined channel, however. The operation of the invention in this example could be initiated in any suitable manner,

4 such as by a i elay starter switch, not shown, interlocking with the ignition system for the engine. Sensor 9 automatically drives driver 16 whenever exhaust noise is experienced, and as described previously, the cancelling waves'are produced in cancelling tube 5.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims which particularly point out and distinctly claim the subject matter which is regarded as the invention.

We claim:

1. An active noise reduction system for a noise source, comprising:

a first sound transmission member defining a sound channel for the noise source;

a second sound transmission member defining a second sound channel joined to said first sound channel at a common junction and extending outwardly from said first sound channel;

a sound sensor transducer coupled'to the first sound transmission member and generating an electrical signal corresponding in frequency with and proportional to the sound in the first sound channel at the point of coupling, a driver member connected to and actuated by said transducer and generating and sending cancelling sound waves through said second sound channel to the first sound transmission member to meet the sound waves from the noise source at said common junction, and

said first and second sound transmission members being straight tubes and joined with an angle of less than and generally in a V-configuration and with an exhaust opening located at the apex of the V-configuration.

2. An active noise reduction system for a noise source, comprising:

a first sound transmission member defining a sound channel for the noise source;

a second sound transmission member defining a second sound channel joined to said first sound channel at a common junction and extending outwardly from said first sound channel;

a sound sensor transducer coupled to the first sound transmission member and generating an electrical signal corresponding in frequency with and proportional to the sound in the first sound channel at the point of coupling, a driver member connected to and actuated by said transducer and generating and sending cancelling sound waves through said second sound channel to the first sound transmission member to meet the sound waves from the noise source at said common junction, and

a phase change and amplification stage connected to said transducer to receive said electrical signal and to said driver member and producing generally a phase inversion,

said sensor transducer and said driver member are spaced generally equidistant from the intersection of said first and second sound channels in the direction toward the noise source.

3. An active noise reduction system for a noise source, comprising:

j a second sound transmission member, said member being straight and substantiallyshorter than the first member and defining a second confining sound channel joined to said first sound channel at a common joint and extending outwardly from said first sound channel and rearwardly toward said input end at a selected angle;

said selected angle being less than 90 to define a V- configuration and selected to establish essentially coincident planes for the first sound waves and the sound transducer means connected to said first sound cancelling sound waves at the common joint.

transmission member and to the input portion of 4. The apparatus of claim 3 wherein said selected said second sound transmission member in spaced 10 angle is of the order of 30. relation to the connection to the first transmission 5. The apparatus of claim 3 wherein the diameter of member and sending cancelling sound waves through said second sound channel to the first less than the noise wave length. sound transmission member to meet the sound said first sound transmission member is substantially-

Claims (5)

1. An active noise reduction system for a noise source, comprising: a first sound transmission member defining a sound chaNnel for the noise source; a second sound transmission member defining a second sound channel joined to said first sound channel at a common junction and extending outwardly from said first sound channel; a sound sensor transducer coupled to the first sound transmission member and generating an electrical signal corresponding in frequency with and proportional to the sound in the first sound channel at the point of coupling, a driver member connected to and actuated by said transducer and generating and sending cancelling sound waves through said second sound channel to the first sound transmission member to meet the sound waves from the noise source at said common junction, and said first and second sound transmission members being straight tubes and joined with an angle of less than 90* and generally in a V-configuration and with an exhaust opening located at the apex of the V-configuration.
2. An active noise reduction system for a noise source, comprising: a first sound transmission member defining a sound channel for the noise source; a second sound transmission member defining a second sound channel joined to said first sound channel at a common junction and extending outwardly from said first sound channel; a sound sensor transducer coupled to the first sound transmission member and generating an electrical signal corresponding in frequency with and proportional to the sound in the first sound channel at the point of coupling, a driver member connected to and actuated by said transducer and generating and sending cancelling sound waves through said second sound channel to the first sound transmission member to meet the sound waves from the noise source at said common junction, and a phase change and amplification stage connected to said transducer to receive said electrical signal and to said driver member and producing generally a 180* phase inversion, said sensor transducer and said driver member are spaced generally equidistant from the intersection of said first and second sound channels in the direction toward the noise source.
3. An active noise reduction system for a noise source, comprising: a first sound transmission member defining a confining sound channel having an input end for transmission of first sound waves from the noise source; a second sound transmission member, said member being straight and substantially shorter than the first member and defining a second confining sound channel joined to said first sound channel at a common joint and extending outwardly from said first sound channel and rearwardly toward said input end at a selected angle; sound transducer means connected to said first sound transmission member and to the input portion of said second sound transmission member in spaced relation to the connection to the first transmission member and sending cancelling sound waves through said second sound channel to the first sound transmission member to meet the sound waves from the noise source with the cancelling sound waves being of corresponding amplitude and of an opposite phase from the first sound waves; and said selected angle being less than 90* to define a V-configuration and selected to establish essentially coincident planes for the first sound waves and the cancelling sound waves at the common joint.
4. The apparatus of claim 3 wherein said selected angle is of the order of 30*.
5. The apparatus of claim 3 wherein the diameter of said first sound transmission member is substantially less than the noise wave length.
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Cited By (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3936606A (en) * 1971-12-07 1976-02-03 Wanke Ronald L Acoustic abatement method and apparatus
US4044203A (en) * 1972-11-24 1977-08-23 National Research Development Corporation Active control of sound waves
US4177874A (en) * 1977-04-01 1979-12-11 Agence Nationale De Valorisation De La Recherche (Anvar) Active acoustic sound absorber device
US4185167A (en) * 1976-06-28 1980-01-22 Acoustical Design Incorporated Sound masking package
US4231228A (en) * 1979-08-03 1980-11-04 Carrier Corporation Combination process tube and vibration attenuator for a refrigeration circuit
EP0040462A1 (en) * 1980-05-16 1981-11-25 Bose Corporation Electroacoustical audible noise reducing apparatus
FR2495809A1 (en) * 1980-12-05 1982-06-11 Lord Corp Device attenuation of the sound vibrations and vibration supression
FR2523658A1 (en) * 1982-03-17 1983-09-23 Deutsche Forsch Luft Raumfahrt Turbomachinery has low noise
US4489441A (en) * 1979-11-21 1984-12-18 Sound Attenuators Limited Method and apparatus for cancelling vibration
WO1989007701A1 (en) * 1988-02-19 1989-08-24 Noise Cancellation Technologies, Inc. Active sound attenuation system for engine exhaust systems and the like
US5097923A (en) * 1988-02-19 1992-03-24 Noise Cancellation Technologies, Inc. Active sound attenation system for engine exhaust systems and the like
US5119427A (en) * 1988-03-14 1992-06-02 Hersh Alan S Extended frequency range Helmholtz resonators
US5135079A (en) * 1990-02-28 1992-08-04 Kabushiki Kaisha Toshiba Noise prevention apparatus for a cable winch elevator
US5255321A (en) * 1990-12-05 1993-10-19 Harman International Industries, Inc. Acoustic transducer for automotive noise cancellation
US5327496A (en) * 1993-06-30 1994-07-05 Iowa State University Research Foundation, Inc. Communication device, apparatus, and method utilizing pseudonoise signal for acoustical echo cancellation
US5416845A (en) * 1993-04-27 1995-05-16 Noise Cancellation Technologies, Inc. Single and multiple channel block adaptive methods and apparatus for active sound and vibration control
EP0642115A3 (en) * 1993-08-06 1995-05-17 Shinko Electric Co Ltd Vibratory parts-feeder apparatus.
US5418873A (en) * 1993-09-09 1995-05-23 Digisonix, Inc. Active acoustic attenuation system with indirect error sensing
US5452265A (en) * 1991-07-01 1995-09-19 The United States Of America As Represented By The Secretary Of The Navy Active acoustic impedance modification arrangement for controlling sound interaction
US5541373A (en) * 1994-09-06 1996-07-30 Digisonix, Inc. Active exhaust silencer
US5662136A (en) * 1995-09-11 1997-09-02 Defense Research Technologies, Inc. Acousto-fluidic driver for active control of turbofan engine noise
US5693918A (en) * 1994-09-06 1997-12-02 Digisonix, Inc. Active exhaust silencer
US5967863A (en) * 1998-04-15 1999-10-19 Marchant; Gary R. Trolling motor
US6461144B1 (en) * 1999-05-07 2002-10-08 Alstom (Switzerland) Ltd Method of controlling thermoacoustic vibrations in a combustion system, and combustion system
US20030215101A1 (en) * 2002-05-15 2003-11-20 Siemens Vdo Automotive, Inc. Active noise control system with an elongated transmission member
EP1724527A1 (en) * 2005-05-13 2006-11-22 Siemens Aktiengesellschaft Combustion chamber and method of suppressing combustion vibrations
WO2008034943A1 (en) * 2006-09-21 2008-03-27 Wärtsilä Finland Oy Exhaust system for a piston engine and method of damping pressure vibration in an exhaust system of a piston engine
US20080175717A1 (en) * 2007-01-24 2008-07-24 Johnson Controls Technology Company System and method of operation of multiple screw compressors with continuously variable speed to provide noise cancellation
US20090240375A1 (en) * 2008-03-18 2009-09-24 Douglas Allen Pfau Vibration control system
US20100252358A1 (en) * 2009-04-06 2010-10-07 International Business Machine Corporation Airflow Optimization and Noise Reduction in Computer Systems
US9253556B1 (en) 2013-08-29 2016-02-02 ConcealFab Corporation Dissipative system for increasing audio entropy thereby diminishing auditory perception
US9286882B1 (en) 2012-03-07 2016-03-15 Great Lakes Sound & Vibration, Inc. Systems and methods for active exhaust noise cancellation

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US2043416A (en) * 1933-01-27 1936-06-09 Lueg Paul Process of silencing sound oscillations
US3071752A (en) * 1958-01-02 1963-01-01 Strasberg Murray Interference reduction apparatus
US3396812A (en) * 1967-07-05 1968-08-13 Arvin Ind Inc Acoustic quarter wave tube

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2043416A (en) * 1933-01-27 1936-06-09 Lueg Paul Process of silencing sound oscillations
US3071752A (en) * 1958-01-02 1963-01-01 Strasberg Murray Interference reduction apparatus
US3396812A (en) * 1967-07-05 1968-08-13 Arvin Ind Inc Acoustic quarter wave tube

Cited By (40)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3936606A (en) * 1971-12-07 1976-02-03 Wanke Ronald L Acoustic abatement method and apparatus
US4044203A (en) * 1972-11-24 1977-08-23 National Research Development Corporation Active control of sound waves
US4185167A (en) * 1976-06-28 1980-01-22 Acoustical Design Incorporated Sound masking package
US4177874A (en) * 1977-04-01 1979-12-11 Agence Nationale De Valorisation De La Recherche (Anvar) Active acoustic sound absorber device
US4231228A (en) * 1979-08-03 1980-11-04 Carrier Corporation Combination process tube and vibration attenuator for a refrigeration circuit
US4489441A (en) * 1979-11-21 1984-12-18 Sound Attenuators Limited Method and apparatus for cancelling vibration
EP0040462A1 (en) * 1980-05-16 1981-11-25 Bose Corporation Electroacoustical audible noise reducing apparatus
FR2495809A1 (en) * 1980-12-05 1982-06-11 Lord Corp Device attenuation of the sound vibrations and vibration supression
DE3144052A1 (en) * 1980-12-05 1982-07-08 Lord Corp "Active acoustic daempfungseinrichtung"
US4473906A (en) * 1980-12-05 1984-09-25 Lord Corporation Active acoustic attenuator
FR2523658A1 (en) * 1982-03-17 1983-09-23 Deutsche Forsch Luft Raumfahrt Turbomachinery has low noise
WO1989007701A1 (en) * 1988-02-19 1989-08-24 Noise Cancellation Technologies, Inc. Active sound attenuation system for engine exhaust systems and the like
US5097923A (en) * 1988-02-19 1992-03-24 Noise Cancellation Technologies, Inc. Active sound attenation system for engine exhaust systems and the like
US5119427A (en) * 1988-03-14 1992-06-02 Hersh Alan S Extended frequency range Helmholtz resonators
US5135079A (en) * 1990-02-28 1992-08-04 Kabushiki Kaisha Toshiba Noise prevention apparatus for a cable winch elevator
US5255321A (en) * 1990-12-05 1993-10-19 Harman International Industries, Inc. Acoustic transducer for automotive noise cancellation
US5452265A (en) * 1991-07-01 1995-09-19 The United States Of America As Represented By The Secretary Of The Navy Active acoustic impedance modification arrangement for controlling sound interaction
US5416845A (en) * 1993-04-27 1995-05-16 Noise Cancellation Technologies, Inc. Single and multiple channel block adaptive methods and apparatus for active sound and vibration control
USRE35574E (en) * 1993-06-30 1997-07-29 Iowa State University Research Foundation, Inc. Communication device apparatus and method utilizing pseudonoise signal for acoustical echo cancellation
WO1995001681A1 (en) * 1993-06-30 1995-01-12 Iowa State University Research Foundation, Inc. Communication device, apparatus, and method utilizing pseudonoise signal for acoustical echo cancellation
US5327496A (en) * 1993-06-30 1994-07-05 Iowa State University Research Foundation, Inc. Communication device, apparatus, and method utilizing pseudonoise signal for acoustical echo cancellation
EP0642115A3 (en) * 1993-08-06 1995-05-17 Shinko Electric Co Ltd Vibratory parts-feeder apparatus.
US5494151A (en) * 1993-08-06 1996-02-27 Shinko Electric Co., Ltd. Vibratory parts-feeder apparatus
US5418873A (en) * 1993-09-09 1995-05-23 Digisonix, Inc. Active acoustic attenuation system with indirect error sensing
US5541373A (en) * 1994-09-06 1996-07-30 Digisonix, Inc. Active exhaust silencer
US5693918A (en) * 1994-09-06 1997-12-02 Digisonix, Inc. Active exhaust silencer
US5662136A (en) * 1995-09-11 1997-09-02 Defense Research Technologies, Inc. Acousto-fluidic driver for active control of turbofan engine noise
US5967863A (en) * 1998-04-15 1999-10-19 Marchant; Gary R. Trolling motor
US6461144B1 (en) * 1999-05-07 2002-10-08 Alstom (Switzerland) Ltd Method of controlling thermoacoustic vibrations in a combustion system, and combustion system
US20030215101A1 (en) * 2002-05-15 2003-11-20 Siemens Vdo Automotive, Inc. Active noise control system with an elongated transmission member
WO2003098594A1 (en) * 2002-05-15 2003-11-27 Siemens Vdo Automotive Inc. Active noise control system with an elongated transmission member
EP1724527A1 (en) * 2005-05-13 2006-11-22 Siemens Aktiengesellschaft Combustion chamber and method of suppressing combustion vibrations
WO2008034943A1 (en) * 2006-09-21 2008-03-27 Wärtsilä Finland Oy Exhaust system for a piston engine and method of damping pressure vibration in an exhaust system of a piston engine
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