Abstract: The invention uses tubes for the reduction of radiated duct noise. The tubes may be used to attenuate narrow band noise by diverting a portion of the acoustic energy through the tubes back into the duct. Upon reintroducing the diverted flow out of phase with the primary flow, acoustic cancellation is achieved. The frequency at which this occurs is dependent on the difference in the path lengths through the tubes and the separation distance—the distance separating the inlet and outlet of the tube. This invention can be used over varying frequency ranges by using an arrangement of flexible, constant length tubes. The effective frequency range is tailored by varying the separation distance and also allows the varying the angular arrangement of the tubes for more effective attenuation of spinning modes having varying propagation angle.

Abstract: The present invention relates to a noise attenuating window comprised of two panes of glass separated by a spacer tube. The spacer tube contains T-shaped acoustic resonator capable of targeting a single mode or multiple-mode to be attenuated.

Abstract: A wind turbine comprising at least a blade (11) having an aerodynamic profile with a leading edge (13), a trailing edge (15) and suction and pressure sides between the leading edge (13) and the trailing edge (15) that includes an anti-noise device (31) placed on the suction side formed by elements (33) that modify the frequency spectra of the boundary layer noise. Preferably the anti-noise device (31) is placed on the suction side between two sections corresponding to chord positions in the range of 40%-95% of -the chord length, measured from the leading edge (13).

Abstract: A resonator for an induction system includes an inlet and outlet with a resonator cavity arranged therebetween. A tube is arranged within the resonator cavity and at least partially extends between the inlet and outlet. In one example, at least one supplemental noise attenuation device is in communication with the arcuate tube, such as a quarter wave tube and/or Helmholtz resonator. A large opening is provided in the tube that opens into the resonator cavity. In one example, the large opening is arranged on an outer radius side and faces a large cavity portion of the resonator cavity. Additional supplemental noise attenuation is provided by a collar arranged concentrically relative to the tube providing an annular quarter wave tube that is coaxial with the direction of flow from the outlet.

Abstract: A duct for an induction system is provided that has an effective length between an inlet and outlet. An aperture is provided a wall of the duct at a location corresponding to a pipe resonance for attenuating noise at the pipe resonance frequency. In one example, the aperture is provided using a cluster of holes arranged at the location. Multiple apertures are arranged about a circumference of the duct, for example, at opposing sides of the duct. In one example, an aperture is provided at a distance of approximately one quarter the effective length from both the inlet and the outlet. A porous non-woven structure is arranged over the aperture to minimize pressure losses associated with the aperture.

Abstract: An assembly useful in reducing aircraft engine noise such as turbofan engine noise (730) comprises: (1) at least one tube “H-Q” having an inlet end (738), an outlet end (740) and a central tube portion therebetween; an (ii) at least one actuator operatively interconnected to at least one tube, wherein the actuator is capable of causing dynamic response by the tube. The assembly of this invention may be used in a method for reducing noise, the method comprising: (a) providing means for generating non-uniform noise energy about an inner surface and within a disclosure having at least an inlet; (b) providing an assembly for reducing noise comprising; (i) at least one tube having an inlet end, an outlet end and a central tube portion therebetween, and (ii) at least one actuator operatively interconnected to at least one tube, wherein the actuator is capable of causing dynamic response by the tube; and (c) directing at least a portion of the non-uniform noise into the assembly.

Abstract: An active countersound system for actively reducing the sound waves of primary sound waves, with a regulator unit, an error sensor, a reference sensor and several secondary actuators.

Abstract: A noise control system operable within a box-like structure provided by the dual bulkhead plenum of the vehicle dashboard positioned within the transfer path along which the noise is being transmitted from the source of the generated noise to the receiver of the noise in the passenger compartment of an automobile. The plenum is divided into discrete chambers into each of which is provided smart materials affixed to the walls of the plenum to be operable for selectively changing a property characteristic of the chambers to vary the acoustic resonance of the plenum and change the effectiveness of controlling the transmission of noise energy therethrough. A controller is coupled to the smart materials to change said property characteristic of the smart material in response to noise cancellation requirements.

Abstract: A plurality of openings are provided on the surface of a body casing which comprises a noise reduction chamber, and plate members (a reflecting plate and a sound waves introduction plate) are provided extending from an edge of each opening to the noise reduction chamber. The opening edges at which these plate members are attached have acute corners or rounded corners.

Abstract: A gaming machine comprises a sound signal output device, a plurality of attenuators, a signal bus and a speaker. The sound signal output device outputs plural sound signals including a BGM signal and a game effect sound signal in parallel. The attenuator attenuates at least the BGM signal of the plural sound signals outputted from the sound signal output device. The signal bus is adapted to input all the plural sound signals including the BGM signal attenuated in the attenuator and transmits the sound signals. The speaker converts the sound signals transmitted through the signal bus into sound waves and then turns up the sound waves.

Abstract: An interference-based exhaust noise attenuation device and method for exhaust flow from an internal combustion engine that generates compressive waves in the exhaust flow. The device includes at least a direct path for the exhaust flow; a looped path for the exhaust flow, with volumes of the direct path and the looped path differing by an amount that results in a staggered rearrangement of the compressive waves in the paths; a splitter that splits the exhaust flow into the direct path and the looped path; and a merger that merges the exhaust flow from the direct path and the looped path. When the exhaust flow from the direct path and the looped path are merged, at least some noise cancellation occurs. In other embodiments, plural direct paths, looped paths, splitters, and/or mergers can be used in various combinations.

Abstract: An apparatus for attenuating noise emanating from a cabinet housing noise-generating equipment includes a frame including at least one support member configured to be mountable on the cabinet, proximate the noise-generating equipment, at least one noise attenuation device mounted to each support member proximate the noise-generating equipment, the at least one noise attenuation device comprising a sound input device for receiving a noise signal output from the noise-generating equipment, a processing device for determining characteristics of the noise signal and generating a cancellation signal which is identical to the noise signal but approximately 180 degrees out-of-phase with the noise signal, and a sound output device for outputting the cancellation signal proximate the noise-generating equipment, to attenuate the noise emanating from the cabinet; and a noise absorption member mounted on each support member, the noise absorption members define surfaces that form sides of airflow channels through the appa

Abstract: An electronic apparatus includes a drive for recording/reproducing a recording medium, and a sound absorbing member having a Helmholtz resonator for insulating sounds at a predetermined frequency among sounds generated by the drive.

Abstract: An active sound muffler for reducing a sound to be reduced as emitted from a sound source located at one of the opposite sides of a sound insulating wall and diffracted and transmitted to the other side, the muffler comprises a control loudspeaker arranged at the front end or the other side of the sound insulating wall and adapted to output a control sound with a predetermined amplitude and a predetermined phase, a control microphone arranged above the sound insulating wall and adapted to gauge the sound pressure or the acoustic intensity of the sound to be reduced and that of the control sound and a control circuit for controlling the output of the control loudspeaker so as to minimize the sound pressure or the acoustic intensity, whichever appropriate, based on the outcome of gauging of the control microphone, and the control loudspeaker showing a line sound source characteristic.

Abstract: The present invention relates to an active muffler for an exhaust gas system of an internal combustion engine, in particular in a motor vehicle, having at least one antinoise generator for applying antinoise to the exhaust gas, whereby the antinoise generator has a diaphragm drive with which it is coupled via at least one coupling element in a thermally conducting and noise-reducing manner to an outside wall of the muffler, which is in contact with the environment.

Abstract: An active exhaust muffler for an exhaust system of an internal combustion engine, having a housing through which a pipe system passes, the pipe system designed to be permeable for airborne sound in a first space, having an antisound generator which is arranged in a second space and antisound acting upon a third space through a wall opening during operation, the wall opening being provided in a partition that separates the second space from the third space, whereby airborne sound is transmitted from the first space to the third space through a sound outlet. To increase the lifetime of the antisound generator and thus the exhaust muffler, a labyrinth is provided in the third space, blocking a direct path between the sound outlet and the wall opening, and providing at least one indirect bypass for the propagation of airborne sound between the sound outlet and the wall opening.

Abstract: An active muffler (1) for an exhaust system (2) of an internal combustion engine has a first space (3) and a second space (4) that is separated from the former via a partition (5). The partition (5) has a wall opening (6) into which is inserted an electronic sound absorber (7) having a chassis (8) and a diaphragm (9). During operation, the electronic sound absorber directs anti-sound toward the first space (3) and thereby reduces the sound emission generated by the exhaust system (2). The chassis (8) of the electronic sound absorber (7) and the partition (5) are made in one piece.

Abstract: A noise-suppressing receiver is provided. A noise pick-up and a receiver are fixed within a cylinder-like body. An insulation layer is set between the noise pick-up and the receiver. The insulation layer divides the cylinder-like body into a receiver module and a noise-collecting module. A reticulate cover is provided at an end of the cylinder-like body, and a front cap is provided on the other end. A circuit device is added onto the inner side of the front cap described above. The invention has the stronger capability of attenuating environmental noise and the good effect of suppressing noise, because of its unique structure and the corresponding circuit device.

Abstract: A pipe has an innermost layer, outside of which there is an inner electrode layer, outside of which there is an insulating layer, outside of which there is an outer electrode layer. The innermost layer is made of plastic by continuous extrusion and the insulating layer is made of foamed plastic.

Abstract: A process and system for noise reduction in multi-engine propeller-driven aircraft. The parameters of at least two propellers are adjusted with regard to frequency, amplitude, and phase so that the sound fields of the propellers are attenuated or completely extinguished by interference in the area of the closest aircraft fuselage.

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: An air intake silencer includes an air inlet pipe and at least one tuning tube in fluid communication with the air inlet pipe. A first length and second length of the air inlet pipe and the tuning tube, respectively, are selected to produce one-half wavelength cancellation of a selected frequency of engine noise. A plurality of tuning tubes located in a wrap-around relationship with on another may tune different frequencies of noise in a compact silencing unit. The air inlet pipe and tuning tube may be integrally formed into an air intake manifold that silences one or more engine air intake inlets, and the air intake silencer may be integrated into a motor cover.

Abstract: Disclosed is a segmented mixing device for reducing jet engine exhaust noise wherein mixing is enhanced between adjacent exhaust flows and between exhaust flow and free-stream flow. The device does so with a very small degradation in aircraft performance. The device is a segmented, triangular or trapezoidal shaped, curved extension to a nozzle's sleeve that results in a serrated trailing edge. The nozzle extensions enhance the natural free mixing of the jet's exhaust flows and therefore reduce the acoustic energy associated with the velocity differences between the streams in which they are imbedded. The novel structure forces adjacent flows to penetrate into one another to a greater depth than that achievable with free mixing and results in a more uniform flow in a shorter stream wise distance while limiting high frequency noise through utilization of root radii in the order of 15 to 20% of the segment's width at the intersection of a parent nozzle.

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: 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 vibration reducing apparatus comprising, a baffle subject to vibration, a first electroacoustical transducer characterized by a first mass seated in the baffle, a second electromechanical transducer mechanically connected to said first transducer or said baffle in the vicinity of the periphery of the first transducer. The rear sides of the diaphragms of the first and the second transducer are not connected to the listening area. The first transducer and the second transducer are constructed and arranged to receive a common electrical signal so that the movable element in the first transducer and the movable element in the second transducer move in phase opposition in response to the common electrical signal to significantly reduce the vibrating force imparted to the baffle.

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: An air introduction system (10) provides an active noise control system which includes a speaker assembly (28) in which the speaker support ring (36) is mounted to a speaker housing (32) without fasteners. In one speaker assembly, the speaker housing includes a plurality of extensions (40) which extend radially from an outer periphery of the speaker housing (32). The speaker support ring includes an edge (42) which at least partially surrounds the extensions (40). In another speaker assembly, the speaker support ring (50) includes a plurality of apertures (52) through a flange (54) which closely fits a speaker housing (32). The housing edge (54) and the speaker protection cone edge (56) are heated to a melting point of the material and the speaker support ring (50) is sandwiched therebetween. Heated material from the housing edge and the speaker protection cone edge pass through the apertures (52) to provide an effective bond therebetween.

Abstract: An actuator rail assembly for conveying an actuating fluid under pressure to at least one fuel injector, include an elongate fluid passageway being defined in a rail. A fluid inlet port is in fluid communication with the fluid passageway, the inlet port being fluidly couplable to a source of actuating fluid under pressure. A respective fluid outlet port is associated with each respective fuel injector and being fluidly couplable thereto for conveying actuating fluid to the respective fuel injector; and at least one fluid cavity having at least one throttling orifice, the orifice effecting fluid communication between the fluid cavity and the fluid passageway. An acoustic wave attenuator and a method of attenuation are also included.

Abstract: Apparatus for suppressing fluid-borne noise in a fluid conduit (12 or 12a) that includes a vibration sensor (36, 36a or 36b) for operative coupling to the conduit for providing an electrical sensor signal as a function of fluid pressure fluctuations in the conduit. A piezoelectric actuator (40, 40a or 40b) is adapted to be mounted on the conduit for imparting pressure fluctuations to fluid in the conduit. An electronic controller (38, 38a or 38b) is responsive to the sensor signal for energizing the actuator 180° out of phase with fluid pressure fluctuations sensed by the sensor. The sensor may be either closely coupled to the actuator, or separate from the actuator and disposed upstream of the actuator with respect to the direction of fluid flow through the conduit. The sensor in the preferred embodiments of the invention comprises a piezoelectric sensor, and the actuator comprises a stack of piezoelectric elements.

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 vehicle air supply noise attenuation system utilizes both active and passive methods of noise attenuation. A helmholtz resonator communicates with an air supply duct, and is designed to attenuate a narrow band of noise. An active noise control system, including a speaker and an electronic controller, is mounted within the resonator volume and attenuates noise over a wider band of frequencies. The combination of the active and passive noise control attenuates noise over a wide band of frequencies without requiring an overly large speaker.

Abstract: Disclosed is a means for reducing jet engine exhaust noise wherein mixing is enhanced between adjacent exhaust flows and between exhaust flow and free-stream flow. The device does so with a very small degradation in aircraft performance. The device is a segmented, triangular or trapezoidal shaped, curved extension to a nozzle's sleeve that results in a serrated trailing edge. The nozzle extensions enhance the natural free mixing of the jet's exhaust flows and therefore reduce the acoustic energy associated with the velocity differences between the streams in which they are imbedded. The novel structure forces adjacent flows to penetrate into one another to a greater depth than that achievable with free mixing and results in a more uniform flow in a shorter stream wise distance.

Abstract: An air induction system comprises an air induction body, a speaker with a first diaphragm disposed about the air induction body, and a second diaphragm spaced from the first diaphragm. A signal is generated from the first diaphragm and transmitted to the second diaphragm. The second diaphragm generates a noise attenuating sound.

Abstract: An active noise cancellation system (20) includes using a frequency domain response of a secondary path (44) of the system. The frequency domain response information provides an indication of a desired magnitude and phase of a reference signal that is used for generating a cancellation signal that drives a speaker (28) to achieve the desired amount of noise cancellation. Using a frequency domain response greatly reduces the number of computations required and the amount of memory used within the system controller. In one example, a reference signal adjustment module (40) applies the desired magnitude and phase adjustments to a reference signal having a known frequency. In another example, the referenced signal tone generator (22, 40) incorporates the desired amplitude and phase in the reference signal.

Abstract: An air introduction system (10) provides an active noise control system which includes a speaker assembly (28) in which the speaker support ring (36) is mounted to a speaker housing (32) without fasteners. In one speaker assembly, the speaker housing includes a plurality of extensions (40) which extend radially from an outer periphery of the speaker housing (32). The speaker support ring includes an edge (42) which at least partially surrounds the extensions (40). In another speaker assembly, the speaker support ring (50) includes a plurality of apertures (52) through a flange (54) which closely fits a speaker housing (32). The housing edge (54) and the speaker protection cone edge (56) are heated to a melting point of the material and the speaker support ring (50) is sandwiched therebetween. Heated material from the housing edge and the speaker protection cone edge pass through the apertures (52) to provide an effective bond therebetween.

Abstract: An air introduction system (b 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: An air induction system for a vehicle engine includes a sensor assembly for monitoring particulate concentration. The sensor assembly is mounted within an air intake housing, which has an inlet and an outlet. An airflow passageway extends between the inlet and the outlet to the vehicle engine. An air filter is mounted within the housing to filter particulates from air flowing through the airflow passageway. The sensor assembly can be mounted to an intake manifold or incorporated into a mass airflow sensor. The particulate sensor generates a particulate signal representative of particulate concentration entering the vehicle engine via the outlet. The signal is sent to an output device monitored by a vehicle operator.

Abstract: An extrusion apparatus and method, and a tubular product and a pipe made of several different materials.

Abstract: A system and method for the reduction of noise radiated by a vibrating structure at a given frequency are disclosed. In systems of the invention, a radiation-cancelling device that acts like a resiliently supported mass with a significant sound radiating area is attached to the exterior surface of the structure to be quieted. Radiation from such a device, when constructed so that the motion of the vibrating structure provides the driving frequency for oscillation of the spring-mass system in the radiation-cancelling device and so that the natural frequency of the spring-mass system in the radiation-cancelling device is lower than the vibration frequency of the vibrating structure cancels the sound radiating from the (preferably) considerably larger vibrating surface to which it is attached. If appropriate, more than one radiation-cancelling device may be attached to a given vibrating structure in a system according to the invention.

Abstract: An air induction system comprises an air induction body, a speaker with a first diaphragm disposed about the air induction body, and a second diaphragm spaced from the first diaphragm. A signal is generated from the first diaphragm and transmitted to the second diaphragm. The second diaphragm generates a noise attenuating sound.

Abstract: An air induction system for a vehicle engine includes a sensor assembly for monitoring particulate concentration. The sensor assembly is mounted within an air intake housing, which has an inlet and an outlet. An airflow passageway extends between the inlet and the outlet to the vehicle engine. An air filter is mounted within the housing to filter particulates from air flowing through the airflow passageway. The sensor assembly can be mounted to an intake manifold or incorporated into a mass airflow sensor. The particulate sensor generates a particulate signal representative of particulate concentration entering the vehicle engine via the outlet. The signal is sent to an output device monitored by a vehicle operator.

Abstract: This invention provides a muffling panel of a new-type lightweight construction having a function of effectively excluding sounds in low and medium sound ranges and high muffling and sound-absorbing properties in a relatively low frequency band area, and also having at least two parallel diaphragms, a frame body for fixing of the diaphragms and a vibration transmitting mechanism which links to the diaphragms and can mechanically transmit reverse phase vibration, wherein the vibration transmitting mechanism converts vibration of one of the diaphragms which vibrates when receiving a sound into reverse phase vibration thereof to transmit it to the other of the diaphragms, thus causing the other of the diaphragms to displace inward or outward and vibrate simultaneously with one of the diaphragms according to vibration energy of the above original sound.

Abstract: A modular Active Noise Control exhaust silencing system is provided including a housing defining an acoustic enclosure having an acoustic outlet port. A speaker is disposed within the acoustic enclosure and an amplifier is disposed within the housing and connected to the speaker. A microphone is associated with the housing for detecting the exhaust noise. A control unit is disposed within the housing in communication with the microphone for receiving signals therefrom. The control unit determines an anti-noise signal for the amplifier for creating an anti-noise responsive to a detected noise source. A port dish is disposed adjacent to the acoustic outlet port which serves as a noise cancellation aid.

Abstract: An apparatus for mounting a loudspeaker within an enclosure is disclosed. The apparatus includes a loudspeaker mounting plate formed within the enclosure, and a mounting boss formed within the enclosure which is separated from the loudspeaker mounting plate by a fixed distance. The loudspeaker includes a first surface for engaging the loudspeaker mounting plate and a second surface disposed opposite the first surface. A pressure plate is disposed between the second surface of the loudspeaker and the mounting boss. An axial force member is associated with the pressure plate, and the axial force member is operable for applying a force between the pressure plate and the mounting boss for securing the loudspeaker between the loudspeaker mounting plate and the mounting boss.

Abstract: The present invention is a trolling boat motor assembly that provides a motor displaced above the water line which is connected to a propeller shaft below the water line by one of a belt drive assembly, worm gear assembly, or flexible cable drive assembly. The motor is housed above the water line to limit the amount of noise transmitted through the water. There are noise insulating bushings placed beneath the motor to further limit the transmission of noise into the water and thus disturbing the marine life therein. There is a noise inversion device that transmits a signal 180 degrees out of phase from noise detected in the water, thereby reducing the amount of audible noise.

Abstract: The vibration detecting apparatus comprises a pickup 2 encasing a piezoelectric element 8 therein, a cord 3 for transmitting an electric signal output by said piezoelectric element 8, and a noise absorbent member 4 in the form of a lump made of rubber, and formed therein with a cord insert path having at least one direction-changing portion 14a, said noise absorbent member being mounted at a suitable position of said cord. The noise absorbent member is preferably made of low repulsion elastic rubber and is preferably spherical. The cord inser path 14 is preferably in the shape of substantially U. According to the aforementioned construction, noises such as a wind-cut sound and a frictional sound generated at the cord can be effectively removed.

Abstract: The present invention is embodied in an aircraft engine noise absorption system having a resonator cavity for absorbing incident noise except for a residue noise signal having a predominant frequency, the system comprising an actuator providing an actuator acoustic signal, a noise sensor for sensing the predominant frequency, and a controller for setting the actuator acoustic signal to the predominant frequency and varying one of a phase and an amplitude of the actuator acoustic signal to decrease the residue noise signal.

Abstract: A method and apparatus are provided for suppressing flow-induced cavitation n a fluid flow. At least one acoustic transducer is coupled to the fluid flow in a region that is susceptible to the formation of cavitation bubbles. The transducer (or transducers) applies an acoustic field to the fluid flow in order to raise the cavitation threshold pressure of the fluid flow above the total local pressure including the pressure drop induced by the fluid flow and the pressure due to the acoustic field.

Abstract: A system and method of attenuating noise generated in a multicylinder internal combustion engine as a result of opening and closing of the exhaust and intake valves in which cross passages extend between regions of the exhaust and intake manifolds adjacent the exhaust and intake valves of different cylinders in which the exhaust and intake valves open at approximately the same time. The acoustic waves of the noise caused by opening of the exhaust and intake valves respectively are set in mutual opposition to each other to thereby substantially cancel each other. A low mass flexible diaphragm in each cross passage prevents cross flow of exhaust gases while allowing transmission of the acoustic waves. Porous plugs restrict flow to the diaphragm while being sufficiently open to allow free transmission of the noise sound waves to the diaphragm to not impair the mutual cancellation process.