Abstract: The device reduces the intensity of noises with localized outlet like those present in the exhaust pipes of endothermic motors, making use of sound-interferences determined by an elastic vibration by means of springs (10) or (12) or (15) of a rigid rod (6) having its fulcrum in (11) and passing through coupled tubes (1) and (2). The acoustic waves spreading in the exhaust and acting onto blade (7) out of one piece with said rod (6) inside the exhaust pipe (1), determine the vibration of the corresponding blade (8) out of one piece with the opposite part of said rod (6) and housed in the coupled pipe (2) so as to generate vibrations in perfect phase opposition interfering at the exhaust pipe's outlet, thus anulling or strongly reducing the noise.

Abstract: A method and apparatus for muffling motor vehicle engine noise comprises conventional noise attenuation apparatus and techniques as well as a tuning circuit for delivering separate signal outputs to at least two transducers separated along the length of the exhaust conduit. A spacing between the transducers corresponds to the range of tuned exhaust lengths required at various engine speeds within the operating range of the motor vehicle engine. The tuning circuit varies the strength of the signal delivered to each of the transducers to vary the cancellation point within the conduit so as to vary the effective length of the conduit in a manner that maintains a minimum or negative pressure pulse at the valve exhaust port and aids in the exhaustion of combustion gases from the cylinder. As a result, engine performance is improved throughout the operating range of the motor vehicle engine.

Abstract: Active acoustic attenuation apparatus is provided for cancellation of noise from an exhaust pipe (12). A chamber (50) has an input (70) receiving exhaust from the exhaust pipe and directing the exhaust along a flowpath (76) to a chamber output (74). Speakers (88, 90) are transversely spaced and offset from the flowpath and introduce sound into the chamber at a space (56) having a transverse area at least as large as each speaker, to minimize acoustic loading of the speakers and to protect the speakers from the heat of hot exhaust for automotive applications, including electronic mufflers.

Abstract: Apparatus for reducing acoustic transmission from mechanical or acoustic sources by means of a double wall partition, within which an acoustic pressure field is generated by at least one secondary acoustic source. The secondary acoustic source is advantageously placed within the partition, around its edges, or it may be an integral part of a wall of the partition.

Abstract: Method of reducing the overflying noise of airplanes having a propeller den by a piston engine. The propeller is arranged on the engine shaft in such a way that positive components of the engine sound pressure fall on negative components of the propeller sound pressure. It is preferable to use an engine/propeller combination in which the number of engine ignitions per revolution of the propeller shaft divided by the number of the propeller blades is an integer, preferably being equal to 1.

Abstract: The device has an entrance and an exit with two low-restriction venturi sections placed in parallel between the entrance and exit. The entering gas flow is separated into two parts, one to pass through one venturi section and the other to pass through the other venturi section. The two parts reunite as they leave the exit. The venturi sections are substantially identical and each contains at least one venturi. The two sections are axially offset from each other by a distance that is equal to one-quarter of the wavelength of the frequency of a principal noise component so that that particular noise frequency is phase shifted 180 degrees by one venturi section relative to the other with resulting cancellation and significant noise attenuation. Usage in an air induction system of an internal combustion engine for attenuating noise from the engine is illustrated. The device is capable of functioning irrespective of the direction of noise in relation to the direction of gas flow.

Abstract: An acoustic characteristics changing device includes a frame member disposed in an acoustic energy field, electro-acoustic conversion means attached to the frame member to constitute at least a portion of the device, variable impedance means connected as an electrical load to the electro-acoustic conversion means, and impedance control means for controlling an equivalent impedance of the variable impedance means. The equivalent impedance is variably controlled, so that an acoustic impedance and then its decrease frequency or decrease amount can be electrically, continuously and finely controlled.

Abstract: A surge eliminator includes a longitudinal cylindrical housing (10) with rounded ends (12) and (14). Fluid flows into inlet chamber (20) and through pipes (34) to a first dampening chamber (22). The fluid then flows from the chamber (22) to a chamber (24) through pipes (36). Fluid then flows from chamber (24) to an outlet chamber (26) through orifices (38) to an outlet (18). The fluid is continually oriented such that it must turn 180.degree. from the inlet to the outlet in each of the dampening chambers.

Abstract: A noise reducing apparatus in the form of a hollow body comprising two or more passage groups consisting of a plurality of passages. The length of each passage is determined such that the sound waves emitted from the passages of the adjacent passage groups form plane waves which are shifted by a half wavelength so that plane waves interfere each other. The apparatus can be secured to an opening of construction and reduce the level of sound pressure from a sound source without any closed shield construction surrounding the sound source.

Abstract: A Coriolis-type mass flowmeter in which the flow tube is vibrated at a resonance frequency approximately equal to the frequency for forced or natural vibration in a higher anti-symmetric mode, such as the second mode. In the preferred embodiment the flowmeter is symmetrical and has sections of oval cross-section that provide low bending resistance to the vibration at the points where the amplitude of vibration is the largest. The preferred embodiment uses electronic signal detection/processing means that generates two signals proportional to flow tube velocity in the direction of vibration of equal distance but on opposite sides of the plane of symmetry of the tube, generates a sum and a difference of the two signals, integrates the sum, demodulates the integrated signal and the difference of the two signals to produce peak amplitude signals, and divides the peak amplitude signals to produce an output that is proportional to mass flow rate.

Abstract: An active silencer provided in a pipe which has one end reaching the noise source and the other end open, the active silencer being provided with a sound generating means which is provided at the sidewall of the pipe facing inside the pipe, a sound collecting means which is provided outside the pipe close to the other end and which detects noise dissipated from the pipe opening, a phase leading means which outputs a lead phase output signal which is advanced from the phase of an output signal of the sound collecting means by a phase corresponding to a predetermined time determined by the distance between the sound generating means and the sound collecting means; and a drive means which outputs a signal constituting the lead phase output signla inverted in phase as a drive signal for the sound generating means, the predetermined time .tau. being set so that .tau.=L/C, wherein the distance between the sound generating means and the sound collecting means is L and the speed of sound is C.

Abstract: Disclosed herein is an engine noise control device for use in automobiles or the like comprising a noise control member which is attached to an opening of an engine room of an automobile or the like. The noise control member has a plurality of hollow conduit passages penetrating from one of surfaces to the other surface thereof. The hollow conduit passages are so arranged that the length of the conduit passages becomes shorter from the central portion to the peripheral portion of the noise control member. Thereby, a noise-propagating direction is changed by controlling the noise to reduce the energy of sounds radiated and/or diffracted to the outside.

Abstract: An active attenuation system is provided for attenuating the pressure pulses in a liquid flowing in a pipe. The system includes an actuator for introducing nulling pressure pulses into the pipeline having the same frequency, but phase reversed to provide opposite amplitude of the pressure pulses to be attenuated. A plurality of pressure sensors are disposed in the pipe to sense the pressure pulses to be attenuated and these sensors are connected to a pressure transducer amplifier system which, in turn, is electrically connected to a control monitor which adaptively models the responses and continuously adjusts its output to a power amplifier which, in turn, signals the actuator to produce nulling pulses at the desired frequency and amplitude to attenuate the pressure pulses at a desired location, i.e. headbox or pipeline termination, in the liquid flowing through the pipe.

Abstract: Fibrous stock suspension preparation systems include moving parts that generate a vibration impulse flow in the outlet from the preparation system. A counter-vibration impulse generator is connected to the outlet pipe and includes a correcting impulse recorder also connected to the outlet pipe for sensing the vibrations of the flow therepast and for sending a signal to the counter-vibration generator to control the amplitude and/or the frequency of the counter-vibration generator. A further impulse recorder between the stock suspension preparation system and the first mentioned impulse recorder is also connected to the outlet pipe for providing a stock transit time correction signal for correcting the signal of the first mentioned impulse recorder.

Abstract: Apparatus is disclosed for attenuating sound radiated from a vibrating surface into a control volume as comprised of a source of a control signal indicative of the amplitude and frequency content of the sound transmitted from the vibrating surface. An actuator(s) or shaker is directly connected to the vibrating surface for further vibrating the vibrating surface to induce a cancelling sound into the control volume for combining with and attenuating the transmitted sound. A sensor(s) is also disposed within the control volume for detecting the resultant sound indicative of the combination of the cancelling and the transmitted sound to provide an error signal indicative thereof.

Abstract: An ultrasonic transducer comprises a cylindrical housing embedded within a rear bumper of a vehicle and opening backward, a reflecting plate having a parabolic reflecting surface provided within the cylindrical housing along a closed end thereof and facing an open end thereof, and an ultrasonic vibrator provided in an upper wall of the housing at the focus of the reflecting plate for emitting and receiving ultrasonic waves. The ultrasonic transducer transmits ultrasonic waves behind the vehicle and receives ultrasonic waves reflected from an obstacle. The ultrasonic transducer further comprises a projecting member provided on the inner wall of the housing along the open end thereof for dispersing and cancelling the ultrasonic waves entering the housing at angles with respect to the axis of the housing. The projecting member has a smoothly curving cross section having a radius of substantially one fourth to five times the wavelength of the ultrasonic waves emitted by the ultrasonic vibrator.

Abstract: Acoustic pulsations in fluid transmission systems such as gas pipelines, engine exhaust systems and compressed air networks are suppressed by an acoustic filter comprising an enlarged pressure vessel with inlet and outlet conduits arranged such that conduit inlet and outlet openings are at the pressure node of standing pressure waves of the pressure vessel length resonant frequency and odd or even harmonics of the fundamental frequency. The inlet and outlet conduit openings are arranged such that the direction of convection flow and acoustic pulsation modulating flow is transverse to the instantaneous particle velocity of fluid resulting from acoustic pulsations existing in or excitable in the pressure vessel. Inlet and outlet conduits preferably open into the pressure vessel in a generally radial direction with respect to the central longitudinal axis of the vessel.

Abstract: Apparatus for damping a sound field propagating in a fluid propagation medium within a channel (1) having a closed cross-section periphery, including at least one but preferably a plurality of lattice members (2) spaced within the channel (1), each of the lattice members have partition walls subdividing the free channel cross-section into a plurality of partial channels (3) which have a length which is larger than the width of the channels, each lattice member is open at both ends, the length of the partial channels runs parallel the main channel and wherein adjacent partial channels (3) have different length for the sound oscillation state, whereby in the adjacent partial channels local sound pressure differences are produced over their length, which are at least partly compensated by having said partition walls permeable for the propagation medium to permit a local sound pressure transmission from one partial channel into the other.

Abstract: A compact low-resistance muffler for reducing sound levels generated by the pulsatile flow of fluids as, for example, at the intake of a compressor or the exhaust port of an internal combustion piston engine. The muffler or suppressor comprises a pair of adjacent branch passages having a common inlet trunk and a common outlet trunk, one of the branch passages containing a flow-restricting orifice and the other of such branch passages being free of any such restriction.

Abstract: A lined duct is divided into two parallel branches by means of a rigid partition. The phase speed of the fundamental mode in each branch depends on the liner configuration and can differ markedly from the free-space phase speed. When the liners in the two branches are not the same, the corresponding phase speeds will be different and a relative phase lag between the waves in the two branches results. This, in turn, leads to interference between these wave components (and their reflections) both at the exit and entrance of the parallel branch pair. This interference can be exploited for the purpose of obtaining a low-frequency attenuation which is substantially larger than the attenuation of the unpartitioned duct.

Abstract: A pulsation dampener providing high attenuation in a narrow quiet band or frequency. The pulsation dampener is tuned to provide a reflected wave 180.degree. out of phase in the narrow band to cancel the undesired pulsation. A silicone polymer contained by a diaphragm is used as the dampening fluid. The pulsation dampener operation is virtually unaffected by changes in working fluid pressure or density. The latter aspect makes the pulsation dampener particularly well suited for use in well drilling operations where pressure pulses in the drilling fluid are used to transmit information to the surface.

Abstract: A method and device for reducing the noise produced in a turbo-machine by e interaction of the blades of a ring of rotor blades and the vanes of a ring of stator vanes by the creation of a counter-noise of opposed phase. This is achieved by the injection of a fluid into the flow passage of the machine in which the blades and vanes are located. The injection is carried out through orifices located on stationary parts of the machine and equal in number to the vanes of rings of stator vanes, the flow through the orifices being modulated at the frequency of the noise to be reduced and with a phase difference which increases in an incremental manner from one orifice to the next. The phase of the modulated flows injected through the orifices is simultaneously regulated so that the acoustic waves created by the flows are substantially in opposition, with respect to phase, to those of the noise to be reduced.

Abstract: A thin disk acoustic baffle comprising a thin disk of material having a uue combination of acoustical properties and dimensions to provide optimum attenuation of sound transmission between two points. Optimum sound attenuation is achieved by adjusting the thickness, diameter, and location of the thin disk relative to one of the points to be baffled and by selecting the material of the disk to have acoustic properties such that sound waves diffracted around the edges of the disk cancel the direct waves transmitted through the disk at a particular frequency of interest.

Abstract: A device for reducing the noise generated by the blades of at least one r of rotor blades in a turbo-machine by the production of a counter-noise of opposed phase. This is achieved by injection of jets of fluid under pressure through orifices borne by the rotor located near to the periphery of the blades, and the flow of the fluid is modulated at a frequency which is a whole number multiple of the rotational frequency of the rotor shaft. Regulation of phase of the modulated injected fluid is carried out in such a manner that the acoustic waves generated by the injected fluid are substantially in opposition, with respect to phase, to those of the noise to be reduced.

Abstract: The invention relates to active acoustic absorber devices for absorbing the sounds which are emitted by a emitter source and which propagate therefrom, along a pipe. An absorber according to the invention comprises an acoustic tripole which is composed of two auxiliary acoustic sources which constitute a dipole and of a third auxiliary source which constitutes a unipole, these three sources being located in the same acoustic chamber, which chamber is disposed outside the pipe, opens therein through three orifices aligned parallel to the longitudinal axis of the pipe and comprises a transverse plane of symmetry perpendicular to the axis of the pipe.

Abstract: A sound wave propagated along a duct through a fluid contained in the duct is attenuated by generating sound waves from an array of sound sources spaced along the duct. Each source generates two waves travelling in opposite directions, the array being operated so that the resultant of those travelling in the same direction as the unwanted wave interferes destructively with the unwanted wave while the resultant of those travelling in the opposite direction is negligible. The array is operated in response to detection of the unwanted wave, the sound detector(s) being so positioned as to introduce a degree of acoustic coupling between the source array and the detection system.

Abstract: A muffler comprises a plurality of stackable stages 1, 2 and 3. Each stage is comprised of a phase opposition circuit. In each phase opposition circuit exhaust gases are divided into two paths towards an outlet where they are recombined. The difference in length between the two paths equals half a wavelength of a selected frequency.

Abstract: A muffler incorporates a tubular shell that has an acoustically reflective interior circumferential surface. In successive sections taken transversely through the shell, the acoustically reflective surface has at least a portion of its circumference shaped to define at least part of an ellipse or a parabola. Between an inlet into and an outlet from the shell, a fluid flow path extends along an axis lengthwise through the shell. A sound absorptive treatment is disposed along a second axis extending lengthwise through the shell. The treatment is spaced from but communicates with the fluid flow path. At least one of the two axes is defined by corresponding focal points of successive transverse sections taken through the curvilinear portion of the circumference of the acoustically reflective shell surface. In operation, sound emitted from fluid flowing along the fluid flow path is reflected by the reflective shell surface to the sound absorptive treatment.

Abstract: A muffler incorporates a tubular shell that has an acoustically reflective interior circumferential surface. In successive sections taken transversely through the shell, the acoustically reflective surface has at least a portion of its circumference shaped to define at least part of an ellipse or a parabola. Between an inlet into and an outlet from the shell, a fluid flow path extends along an axis lengthwise through the shell. A sound absorptive treatment is disposed along a second axis extending lengthwise through the shell. The treatment is spaced from but communicates with the fluid flow path. At least one of the two axes is defined by corresponding focal points of successive transverse sections taken through the curvilinear portion of the circumference of the acoustically reflective shell surface. In operation, sound emitted from fluid flowing along the fluid flow path is reflected by the reflective shell surface to the sound absorptive treatment.

Abstract: Apparatus for attenuating a sound wave propagating in a given direction along a fluid-containing duct comprises two sound sources spaced along the duct in a given direction; a sound detector between the two sources at a null point at which sound emanating only from the two sources substantially cancels; and means for utilizing the output of the sound detector including a phase-shifter and a frequency-sensitive amplifier to control the operation of the sound sources so that they emit sound in relative antiphase and at equal amplitudes and at such phases relative to the phase of the detected sound that the resultant of the sound radiations emitted in the given direction substantially attenuates the sound wave propagating along the duct.