Abstract: The invention relates to a method and an equipment for attenuating sound in a duct. Sound propagating in a duct is detected by means of a detector (2) and attenuated by using two successive monopole elements (3, 4) in such a way that both elements function as a dipole approximation and the elements are also used to approximatively produce the monopole radiation needed. A dipole control signal is fed to both elements (3, 4) at a phase shift which is 180° between the two elements. In addition, a monopole control signal is fed to the same elements (3, 4), only this time cophasally. Total volume velocities produced by the two elements (3, 4) are combinations of the portions obtained from the monopole and dipole sources.

Abstract: An active noise control system is provided to specify an input transducer, an error transducer, an output transducer and an active noise controller for generating an anti-phase canceling acoustic signal to attenuate an input noise and to output a reduced noise. The active noise control system also performs on-line secondary path modeling. For this purpose the active noise control system comprises, in addition to known systems, a secondary path change detection circuitry (6), a signal distinguishing circuitry (7) and an auxiliary noise control circuitry (8), all of them being used to model said secondary path.

Abstract: An air induction system for an internal combustion engine utilizes localized heat generation to produce a desired acoustic profile that attenuates noise propagated through the air induction system. The noise propagated through the air induction system varies over time to form a variable noise profile. A heat generating mechanism, such as a laser array or electric spark generator, produces a predetermined amount of heat within a localized area adjacent to an inlet to the air duct housing. The predetermined amount of heat is an amount of heat sufficient to produce a desired acoustic energy as a result of rapid air expansion at the localized area. A controller varies the predetermined amount of heat over time to produce a desired acoustic profile that cancels the variable noise profile.

Abstract: An air intake noise reduction apparatus is provided which can effectively reduce air intake noise even with simple construction requiring a small number of components. Four air intake passages 24, 25, 26, 27 which each have different passage lengths are formed by connecting an upper wall 17 and a lower wall 18 of an air intake noise reduction duct 11 which are flattened in a vertical direction with three partition walls 21, 22, 23. Air intake noise can be reduced by making pulsating air interfere with one another which is generated in the plurality of air intake passages 24, 25, 26, 27 which each have the different passage lengths in such a manner as to have different phases shifted from one another. In addition, since the partition walls function as a reinforcement rib, the rigidity of the air intake noise reduction duct 11 can be enhanced.

Abstract: An air induction system includes a duct that defines a passage for airflow to the engine. The duct is substantially clear of obstructions to improve airflow that in turn provides improved engine performance. A speaker generates sounds to provide a desirable engine sound. A controller drives the speaker to generate desired tones and sounds responsive to engine operation. The sounds generated by the speaker enhance, improve and provide desirable and proportional acoustic performance more reflective of the improved engine performance provided by the improved airflow.

Abstract: A sound source device is connected to one end of a pipe arrangement to supply sound into the pipe arrangement. Regenerators are installed to the pipe arrangement. Each regenerator serves as an energy converter that converts energy of an acoustic wave of the sound, which is propagated in the pipe arrangement, into another form of energy. Acoustic wave amplifier/attenuator apparatuses are provided in the pipe arrangement at a corresponding location between the sound source device and a corresponding one of the regenerators. Each acoustic wave amplifier/attenuator apparatus uses thermoacoustic effect to amplify or attenuate the acoustic wave and includes a cold heat exchanger, a hot heat exchanger and a stack that is held between the cold heat exchanger and the hot heat exchanger.

Abstract: An active noise controller includes a duct (2) of a stainless steel having the shape of a pipe and provided with an opening (1) at a first end thereof, and a loudspeaker (3)connected to a second end of the duct (2). The duct (2) is disposed with its opening (1) located at a distance not greater than half the wavelength of a sound produced by a sound source (4) from the sound source (4) so as to face the sound source (4). A sound produced by the vibration of the vibrating member (5) of the loudspeaker (3) travels from the second end of the duct (2) through the duct (2) to the first end of the same, and the sound is radiated toward the sound source (4). The sound radiated through the opening (1) has a frequency substantially equal to that of an unnecessary sound included in the sound produced by the sound source (4), an amplitude substantially equal to that of the unnecessary sound and a phase substantially opposite to that of the unnecessary sound.

Abstract: A Helmholtz resonator includes a chamber at least partially defining a cavity. The chamber has a neck which defines a passage that is in fluid communication with the cavity. The chamber and the neck produce a passive response to a sound wave produced by the internal combustion engine. The sound wave negatively effects engine performance. An active resonator is disposed within the chamber. The active resonator produces a forced response for supplementing the passive response and increasing the band width of the noise attenuating pressure wave. The Helmholtz resonator is in fluid communication with a portion of an air induction system that defines a passageway that carries the sound wave. A driver is connected to the active resonator, which is preferably a loud speaker, to drive the loud speaker and produce the forced response. The driver preferably utilizes a signal source, such as an engine speed signal, to synchronize the forced response with the engine speed.

Abstract: The invention relates to an electroaeroacoustic source (2) placed in a flow (V) or at the edge of a flow, consisting of an electrodynamic or electromagnetic motor means (5) generating an oscillating motion, and an element (3) coupled to the motor means (5) obstructing the flow so as to exert a dynamic action on said flow. This source can be used to produce an electroaeroacoustic system for the active noise control, particularly in a confined flow.

Abstract: An apparatus and a method of voice detection and discrimination apparatus for controlling a voice operated system. A protective ear terminal element in the apparatus protects the ear by providing acoustic attenuation. An inner electroacoustic transducer element on an inner side of the ear terminal element detects a first acoustic field and provides a first electronic signal representing the first acoustic field. An outer electroacoustic transducer element on an outer side of the ear terminal element detects a second acoustic field and provides a second electronic signal representing the second acoustic field. An electronics unit is connected with the electroacoustic transducer elements and includes first and second comparison members.

Abstract: A turbo-charged vehicle engine sound simulator (10) that is designed to function in combination with a vehicle having a coil (92), a tachometer (94), an alternator (96), an engine manifold (98) having a manifold absolute pressure (MAP) sensor (100), and a battery (90). The simulator (10) utilizes an engine RPM source (12), a vacuum pressure switch (14), a turbo-sound storage unit (28), a power amplifier (30), a loudspeaker (32) and a regulated power supply (34) to accurately reproduce the sound that is heard from a blow-off valve on a turbo-charged engine. The simulator (10) allows a person to provide the appearance that his/her vehicle is equipped with a turbo-charger.

Abstract: An air introduction system (10) includes an active noise control system (22) having an environmentally protected microphone (24). A microphone support structure (26) defines a louvered cage (38) over a microphone reception cavity (40). The microphone (24) is mounted to a circuit board (42) which fits within the microphone reception cavity (40). A cover (42) fits into the cavity (40) to encase the microphone (24) therein. An open cell foam (60) surround the microphone (24) and a waterproof material (58) encases the foam (60). The waterproof material (58) includes an excess of material such that waterproof material provides for internal air expansion and contraction. By locating the foam (60) between the microphone (24) and the waterproof material (58) improved transmission of acoustic waves is provided which thereby maintains microphone sensitivity.

Abstract: A method and apparatus for actively influencing the intake noise of an internal combustion engine. The apparatus comprises a controller (7) which senses the actual noise (I) via a microphone (16) and compares the actual noise with a reference noise signal which depends on the engine speed D and at least one further engine parameter P, such as, for example, the throttle (12) position. A comparison signal V generated by comparing the actual noise to the reference noise value is used to adjust a control signal Asum, which also depends on the engine speed D. The control signal is fed to an electromechanical transducer (14) which generates a correcting noise (20) which is superimposed on the intake noise (21) to produce the resultant actual noise (22), which should correspond as closely as possible to the reference noise value.

Abstract: A noise reduction system for use with an exhaust nozzle associated with a jet engine of an aircraft. The noise reduction system employs a plurality of flow-altering components disposed circumferentially about a lip portion of an exhaust nozzle. In one preferred form the flow-altering components each comprise piezoelectric transduction layers. The flow-altering components are caused to move in an oscillating manner by an AC signal applied thereto such that they move into and out of the exhaust gas emitted from the exhaust nozzle to achieve a desired degree of intermixing of the exhaust flow with the flow adjacent the exhaust nozzle. This produces a reduction in the noise generated by the jet engine. The noise reduction can be utilized during takeoff conditions of an aircraft.

Abstract: A ventilation assembly (10) for a window or door assembly is provided with an anti-sound system (80). The anti-sound system may include a sound generator (82), a noise sensor (88) and an error correction noise sensor (100). A control box (86) is provided for the anti-sound system (80). A solar cell (96) may be provided on a weather canopy (14) of the ventilation assembly for providing power to the control box (86). The ventilation assembly may alternatively comprise a wall vent, chimney or stack vent ventilation system.

Abstract: An apparatus for damping acoustic vibrations in a combustor as well as a corresponding combustor arrangement with the apparatus. The apparatus includes a Helmholtz resonator (4) that can be connected via a connecting channel (2) with a combustor (1). The Helmholtz resonator (4) contains a hollow body (6) the volume of which can be changed by adding or draining a fluid via a supply line (5), or is located adjacent to such a hollow body in such a way that the resonance volume (3) of the Helmholtz resonator (4) is changed when the volume of the hollow body (6) is changed. This apparatus makes it possible to adjust the resonance frequency of a Helmholtz resonator arranged inside a pressure container in accordance with the respective current operating point of the combustor to be damped, without having to pass movable components through the pressure container.

Abstract: The present invention relates to noise reduction technology for controlling exhaust noise in internal combustion engines such as an automobile engine and/or noise in a duct of an air delivery system such as air conditioning systems, and more particularly, to an apparatus and a method for controlling exhaust noise in an internal combustion engine or noise in a duct of an air delivery system using a conduit bypass pipe having variable or fixed lengths and dual mufflers.

Abstract: A resonator for noise damping in a sound-conducting tubular channel (2) is provided with an actively controllable sound generator (4) which is arranged in a resonator chamber (12) to generate interference noise (16) to be superimposed on the tubular channel noise. The resonator chamber (12) is connected via a sound-transmitting opening in a tube wall (3) of the tubular channel (2) to the inside of the tubular channel. A measurement signal from a sound sensor (8) arranged in the tubular channel (2), containing information about the sound spectrum in the channel, is connected amplified, to the sound generator (4) with the same frequency and with inverse phase position. To amplify the active suppression of the sound level by the resonator with a resonator of the smallest possible overall size, the sound-transmitting opening in the tube wall is constructed as a peripheral annular gap in the tube wall.

Abstract: An air induction system for an internal combustion engine utilizes localized heat generation to produce a desired acoustic profile that attenuates noise propagated through the air induction system. The noise propagated through the air induction system varies over time to form a variable noise profile. A heat generating mechanism, such as a laser array or electric spark generator, produces a predetermined amount of heat within a localized area adjacent to an inlet to the air duct housing. The predetermined amount of heat is an amount of heat sufficient to produce a desired acoustic energy as a result of rapid air expansion at the localized area. A controller varies the predetermined amount of heat over time to produce a desired acoustic profile that cancels the variable noise profile.

Abstract: An air induction system with active noise control includes a self-cleaning air filter that is integrated within an air intake housing. The self-cleaning air filter filters out contaminants such as dust and dirt particulates from air flowing through the intake housing. The self-cleaning filter is powered and controlled by the same electronic unit that is used to power the active noise control system.

Abstract: An active noise control system (26) includes an error microphone (28), a speaker (29) and an active resonator (30) which communicate with an ANC controller (32). The active resonator is a Helmholtz resonator which is coupled to an air introduction body (19). The resonance frequency of the active resonator is varied in response to the ANC controller (32) which provides logic which responds to sensor signals to eliminate low frequency noise such that the ANC system speaker (29) will effectively control and/or spectral shape the remaining noise.

Abstract: The present invention relates to a smart foam for active noise control in a duct and a device equipped with the same. In particular, the smart foam for the active noise control in a duct according to the present invention comprises: an external ring (52) made out of an elastic porous synthetic resin foam material of a certain length; an internal ring (54) made out of an elastic porous synthetic resin foam to be inserted into the said external ring (52); a ring type PVDF film (60) to be interposed between the said external ring (52) and the internal ring (54) for the radiation of sounds, on the outer and inner surfaces of which film conductive material layers are plated; and lead wires (64) connecting the conductive material layers (62) on the outer and inner surfaces of the said PVDF film (60) to different electrodes and conveying voltages thereto in order to enable the PVDF film (60) to radiate sounds.

Abstract: A flow tube for an induction system with a turbo charger includes a first tube half and a second tube half with a noise attenuation plate positioned between the halves. The noise attenuation plate includes a plurality of holes having varying diameter and depths. The first tube half, the second tube half, and the noise attenuation plate are integrally formed as a single piece during an injection molding process. The noise attenuation plate is folding along a first living hinge to overlap one of the first or second tube halves. The other of the first or second tube halves is folded along a second living hinge to overlap the noise attenuation plate forming a flow tube that defines a flow path. The noise attenuation plate is thus positioned in the flow path. When acoustic energy created by the turbo charger encounters the noise attenuation plate, the change in impedance results in acoustic reflections back toward the turbo charger.

Abstract: The device for the active sound attenuation of a sound signal propagated in a duct comprises: at least first sensor means for a first sound signal, attenuation actuating means supplying an active sound attenuation signal in response to a selected control signal, an electronic control means generating the active sound attenuation signal for the actuating means. The first sensor means and the actuating means are arranged completely inside the duct opposite one another and at a selected distance from the casing of the duct, the axis of symmetry of the radiation of the actuating means and the axis of symmetry of the first sensor means are substantially parallel to the direction of propagation of the sound signal in the duct, and the actuating means are arranged upstream of the first sensor means in the direction of propagation of the sound signal in the duct.

Abstract: Disclosed is a sound masking system including an airflow unit housing at least one speaker generating a masking sound field. The airflow unit is often an air diffuser set into a conventional suspended ceiling comprised of ceiling tiles. The air diffuser provides an acoustic hole in the ceiling plane whereby sound can travel into the room unencumbered by the plane of ceiling tiles. The speaker is housed within the air diffuser and is directed into the room to be treated. The speaker is capable of producing sound waves in a frequency that masks the human voice.

Abstract: An active noise cancellation system (20) for use with an assembly (22) includes adjusting the phase of a reference signal an amount that corresponds to a change in phase of the noise (26) within the system. A non-acoustic sensor (44) provides a signal regarding a position or frequency of a source of noise (28) (i.e., RPM's of a vehicle engine). Control electronics (32) provide a reference signal to the system noise canceling actuator (30) (i.e., a speaker) that includes the phase adjustment responsive to the sensor signal. In one example, the reference signal is delayed an amount of time corresponding to the phase change in the noise (26) as it travels through the system (22). In another example, the phase angle is adjusted.

Abstract: The present invention relates to a smart foam for active noise control in a duct and a device equipped with the same. In particular, the smart foam for the active noise control in a duct according to the present invention comprises: an external ring (52) made out of an elastic porous synthetic resin foam material of a certain length; an internal ring (54) made out of an elastic porous synthetic resin foam to be inserted into the said external ring (52); a ring type PVDF film (60) to be interposed between the said external ring (52) and the internal ring (54) for the radiation of sounds, on the outer and inner surfaces of which film conductive material layers are plated; and lead wires (64) connecting the conductive material layers (62) on the outer and inner surfaces of the said PVDF film (60) to different electrodes and conveying voltages thereto in order to enable the PVDF film (60) to radiate sounds.

Abstract: An active noise cancellation system (26) for controlling engine noise propagation through a vehicle induction system (32) is customizable to achieve a desired engine noise profile. A controller (34) of the active noise cancellation system drives a speaker (36) to generate a noise cancellation sound in a manner consistent with an individual's indicated preference for a specific type of available engine noise profile. By customizing how the speaker is driven, the system customizes the resulting engine noise heard in the passenger compartment. In one example, the system is customizable using a hand held communication device (24) such as a cell phone, a personal digital assistant or a so-called palm top computer. In another example, a resident communication bus on the vehicle is accessed through a user communication interface (28) supported on the vehicle.

Abstract: A modular air induction assembly comprises an air induction body, an air filter operatively attached to the air induction body, and a speaker operatively attached to the air induction body. The modular air induction assembly is then installed into the air induction system of a vehicle during production. The air induction body may also comprise a first portion and a second portion that permits service of the assembly following initial vehicle installation.

Abstract: A noise attenuation system (10) for an air induction system (12) includes an air inlet duct (16) having an open end (18) to draw in air and a loudspeaker (22) mounted within the inlet duct (16) and facing the open end (18) of the inlet duct (16). The air horn (24) is connected to the loudspeaker (22) to tune the sound output and increase the sound power from the loudspeaker (22) to optimize cancellation of noise generated by the air induction system (16) at lower frequencies. An open end (18) of the air horn (24) is positioned within a plane defined by the open end (18) of the air inlet duct (16). A microphone (26) is positioned near the air inlet duct (16) and is in communication with a controller (28). The controller (28) generates an input to the loudspeaker (22). The input to the loudspeaker (22) is out of phase with the noise detected by the microphones (26) to cancel a portion of noise emitted from the open end (18) of the air inlet (16).

Abstract: An active noise attenuation system for an air induction assembly is operably connected to an engine that generates a low frequency noise having a noise profile defining a peak noise. The system has an air inlet duct housing with an inlet and an outlet connected to the engine. A resonator is supported by the housing and is positioned between a speaker assembly and the engine to attenuate the peak noise resulting in an attenuated low frequency engine noise. A microphone senses the attenuated low frequency engine noise and generates an attenuated low frequency engine noise signal. A controller receives and phase shifts the signal and sends the signal to the speaker to generate a sound field to cancel or reduce the attenuated low frequency engine noise signal.

Abstract: A feedforward active noise control system (50) is provided for generating an anti-noise signal to attenuate a noise signal provided through a media. The feedforward active noise control system (50) performs on-line feedback path modeling and feedback path neutralization and includes a reference sensor (16), a secondary source (18), an error sensor (20), and an active noise control system controller (10). The reference sensor (16) receives the noise signal and a feedback signal (22) and generates a primary signal x(n). The secondary source (18) receives a secondary signal s(n) and generates a corresponding anti-noise signal. The error sensor (20) receives a residual signal and generates an error signal e(n) in response. The active noise control system controller (10) receives the primary signal x(n) and the error signal e(n) and generates the secondary signal y(n) while performing on-line feedback path modeling.

Abstract: A first rectifying net, a rectifying grid and a second rectifying net are attached, as a rectifying part upstream of a duct through which air for cooling flows. A noise detection microphone detects noise within the duct. An error detection microphone is placed in the downstream side of the noise to detect error noise. An arithmetic circuit inputs a noise signal of the noise detection microphone, carries out an arithmetic of a transfer function so that an output signal of the error detection microphone becomes minimum, and outputs a control signal to a control sound source. The control sound source radiates a control sound having approximately the same sound pressure as and an opposite phase of the noise within the duct. Thus, the coherence between the noise in the upstream and downstream parts increases, thereby enhancing a sound-muffling effect.

Abstract: The air induction system comprises an air induction body and speaker supported about the air induction body. A control unit communicates with the speaker, controlling its output. The control unit also receives a reference signal from an alternator of a vehicle engine and uses this signal to generate a noise attenuating signal based on the reference signal.

Abstract: A reactive sound attenuator which includes a sensor for detecting a sound parameter in a space, e.g. a duct, consists of a signal amplifier that is used to amplify a detected signal, an electroacoustic transducer and a cavity with at least one membrane. The membrane, which is capable of moving in a vibratory manner, is part of a wall of a space, e.g. a duct wall. A sensor, which is disposed in the immediate vicinity of, in or on the membrane, detects the vibrations of the membrane. The sensor's signal, which is amplified and inverted by the amplifier, controls the membrane vibration via the electroacoustic transducer.

Abstract: An active noise controller includes a duct (2) of a stainless steel having the shape of a pipe and provided with an opening (1) at a first end thereof, and a loudspeaker (3)connected to a second end of the duct (2). The duct (2) is disposed with its opening (1) located at a distance not greater than half the wavelength of a sound produced by a sound source (4) from the sound source (4) so as to face the sound source (4). A sound produced by the vibration of the vibrating member (5) of the loudspeaker (3) travels from the second end of the duct (2) through the duct (2) to the first end of the same, and the sound is radiated toward the sound source (4). The sound radiated through the opening (1) has a frequency substantially equal to that of an unnecessary sound included in the sound produced by the sound source (4), an amplitude substantially equal to that of the unnecessary sound and a phase substantially opposite to that of the unnecessary sound.

Abstract: An active noise attenuation system for an air induction assembly includes a housing that is mounted to a vehicle structure and a speaker assembly that is mounted within the housing to generate a sound field for attenuating noise. The housing defines an air inlet duct open end through which air is drawn. A microphone detects noise and modifies an anti-noise signal that is sent from an electronics center. The electronics center receives the signal, mixes with other engine signals, phase-shifts the signal, and sends the phase-shifted signal to the speaker to attenuate the noise. The speaker includes electrical connections that extend outwardly toward the air inlet duct open end for connection to the electronics center. The microphone and speaker are connected to the electronics center with flex cables.

Abstract: The air induction system comprises an air induction body and speaker disposed about the air induction body. A control unit communicates with the speaker and has at least two modes of noise attenuation signal generation. An engine speed sensor communicates engine speed data to the control unit. An engine load sensor communicates engine load data to the control unit as well. The control unit then selects one of the at least two modes of noise attenuation based on the engine speed data and the engine load data.

Abstract: An apparatus for reducing noise emitted by an electronic or other device and such devices incorporating the noise reducing apparatus. A mechanism for acoustically filtering undesired noise from an electronic device, particularly noise generated by a cooling mechanism is disclosed. In a preferred embodiment, noise is filtered at least in part with an appropriately dimensioned compressible air space. The noise reducing or filtering mechanism may be utilized with portable and non-portable computers, stereos, entertainment equipment and other devices.

Abstract: Embodiments of the present invention described and shown in the specification and drawings include a combination responsive to a sound wave that can be utilized as an acoustic liner and/or an acoustic energy reclamation device. The combination has a first plate having a passage for allowing a portion of the sound wave to pass through, a second plate having a hole, and a third plate having an adjustable compliance. The second plate is located between the first plate and the third plate such that the hole of the second plate is closed to form a chamber that is in fluid communication with the passage, and the compliance of the third plate is adjustable for altering a resonant frequency of the chamber to achieve a desired noise suppression of the sound wave.

Abstract: Pseudo space transmitting signal processing means of the signal processing means simulates the frequency response of the space up to the silencing point from a noise source, while pseudo inverse filter signal processing means simulates an inverse filter characteristic 1/(K×Sp×G1) for canceling the characteristic of the combined frequency response (K×Sp×G1) of K of noise input means, Sp of a secondary sound source speaker, and G1 up to a silencing point from a secondary sound source speaker. The pseudo space transmitting signal processing means and pseudo inverse filter signal processing means set a gain characteristic equal to an original space transmitting characteristic and inverse filter characteristic, respectively.

Abstract: A configuration of providing a microphone in a duct having an air current therein, for use in an active noise reduction device for reducing noise propagating in the duct by producing sounds counteracting the noise, includes an expanded room formed by enlarging an area of a cross section of part of the duct, wherein the cross section is perpendicular to a direction of the air current, and a microphone provided in the expanded room for picking up the noise in order to produce signals for the sounds.

Abstract: The active noise attenuation system comprises a speaker, a control unit in communication with the speaker, and a memory unit in communication with the control unit storing cancellation waveform data. The system uses the stored cancellation waveform data to create a cancellation waveform through a speaker in proximity to an air induction system to thereby attenuate engine noise. Sensors serve to trigger the release of the cancellation waveform as well as to affect the form of the cancellation waveform to ensure noise attenuation.

Abstract: The air induction system comprises an air induction body having a mouth emanating a first sound and a speaker emanating a second sound disposed about the mouth. The mouth has at least a first mouth portion and at least a second mouth portion wherein the first sound is louder at the at least first mouth portion than at the at least second mouth portion. The speaker has at least a first speaker portion and at least a second speaker portion wherein the second sound is louder at the at least first speaker portion than at the at least second speaker portion.

Abstract: The air induction system comprises an air induction body having a mouth. A speaker and microphone are both operatively connected to the air induction body. A support connects the microphone to the air induction body. The support may be rigid and extend over only a portion of the face of the speaker. The support may also be spaced a predetermined distance from the speaker face. This distance may relate to the location of the sound field emitted by the speaker. Both the speaker and microphone are in communication with a control unit. The microphone receives sound and communicates this sound to the control unit. The control unit then generates a noise attenuation sound through the speaker.

Abstract: An apparatus for reducing noise emitted by an electronic or other device and such devices incorporating the noise reducing apparatus. A mechanism for acoustically filtering undesired noise from an electronic device, particularly noise generated by a cooling mechanism is disclosed. In a preferred embodiment, noise is filtered at least in part with an appropriately dimensioned compressible air space. The noise reducing or filtering mechanism may be utilized with portable and non-portable computers, stereos, entertainment equipment and other devices.

Abstract: A method and system for attenuating the effects of unknown, unmeasurable and time-varying exogenous disturbances on multiple-input multiple-output dynamical systems are described. The disturbance rejection system is characterized in terms of an ARMARKOV or predictive model controller. The parameters of this controller are revised in real time at discrete time steps so as to generate an input to the dynamical system that attenuates the effect of the exogenous disturbance on any chosen set of measured outputs of the dynamical system. The method for revising the controller parameters involves the steps of defining a novel retrospective cost function based on windows of past data, calculating a gradient that is based on this cost function, and using an implementable adaptive step size that brings the controller parameters closer to optimal controller parameters after each revision.

Abstract: The present invention is an active-control system for attenuating noise in a duct having a fluid flow. An array of stators having a longitudinal length is positioned axially within the duct. A first array of sound sources capable of generating spinning mode sound and is positioned a distance upstream of a first plane defined by the upstream-most portion of the stators, relative to the fluid flow. The upstream distance is less than the longitudinal length of the stators. A second array of sound sources capable of generating spinning mode sound and is positioned a distance downstream of a second plane defined by the downstream-most portion of the stators, relative to the fluid flow. The downstream distance is less than the longitudinal length of the stators. A controller causes the first and second arrays of sound sources to generate sound including spinning mode sound such that it cancels a portion of the noise within the fluid flow that passes through the stators.

Abstract: A speaker, serving as an additional sound source, is provided close to a noise source, two microphones are arranged on a central axis of a vibration surface of the speaker to be spaced from each other, acoustic intensity of the speaker is measured from outputs of these microphones, and an input to the speaker is controlled by a controller such that acoustic intensity, that is, acoustic power of the speaker is set to be zero or minimized.