Abstract: This invention relates to an improved method of on-line system identification for use with active control systems which requires less computation and reduces the problem of coefficient jitter in the filters of the active control system by using a fixed test signal which is designed to have a particular power spectrum.

Abstract: In an actively sound dampened muffler, the improvement of a venturi effect area producing means adjacent an aperture in said muffler near which is mounted a loudspeaker in an enclosure, the venturi effect area preventing hot exhaust gases from impinging on the loudspeaker.

Abstract: An active noise control system for controlling multiple home appliances and including a power distribution network by which many appliances can be quieted by remotely processing noise signal information and forwarding noise cancelling signals to the appliances through the distribution network.

Abstract: A ducted axial fan for large diameter ducts (11) which includes equidistantly spaced sensors (22,23) upstream and downstream of an axial fan and spaced actuators (24, 26) located around the periphery of said duct to cancel tonal noise caused by the air turbulence generated by the rotation of the fan.

Abstract: An ultra quiet vacuum cleaner having a bag cavity (44), a motor/blower chamber (48) connected to said cavity by a flexible coupling (47) and an active, adaptive noise cancellation controller (52) so configured to quiet the exhaust of the air used to cool the motor/blower unit. Fast compensation and feedback compensation allow use of a straight, short duct (51) for superior cancellation performance.

Abstract: An improved audio system designed to maintain a desired sound at the ear of a listener by using an equalization filter (2). The equalization filter (2) is continuously adjusted in response to the signal (9) from a sensor (8) which monitors the sound close to the listener's ear. The audio system can be combined with an active noise control system (3) to reduce interference from external noise.

Abstract: An active control system for multiple interacting channels to control a constant noise or vibration consisting of first and second sensor means adapted to provide reference and residual signals respectively, a first and second filter means and first and second subtraction means to provide first and second output control signals and means for combining said output signals.

Abstract: A low voltage bender piezo-actuator with multiple, same size piezo layers (11, 12) separated by thin electrically conductive strips (14) and adapted to be affixed to a rigid, vibration transmitting plate (10) to produce noise counter vibrations to prevent noise from passing through the plate.

Abstract: A magnetic bearing control system for a rotating shaft, for example, includes a plurality of electromagnets disposed around and in close proximity to the surface of the shaft. The control system provides a bias current to the electromagnets to maintain the shaft in a null position. Levitation of the shaft is controlled by a levitation controller, and disturbance rejection is effected by a disturbance rejection controller. Flux sensors, suitably located near the electromagnets, determine the magnitude and polarity of the flux resident in the gap between each electromagnet and the shaft. The controller determines the size of the gap based on the flux and generates a corresponding control signal to maintain the position of the shaft within the bearing.

Abstract: A harmonic filter for active or adaptive noise attenuation control systems for obtaining the complex amplitude of a single harmonic component from a signal which contains one or more harmonic components.

Abstract: An electronic muffling device is disclosed for suppressing the noise emitted by an outlet of an exhaust pipe of an engine. The device comprises a housing having an outlet and a plurality of audio transducers. The transducers supply anti-noise to cancel detected unwanted noise. A microphone appropriately positioned to detect residual noise is coupled to a cancellation signal generator, which controls the anti-noise generated by the transducers. Anti-noise and unwanted engine noise propagate through a front volume within the housing so that exhaust gases are transmitted through the housing, but engine noise is canceled before leaving the housing. Exhaust gas may be transmitted into the housing, or may be passed through the housing without leaving the exhaust pipe. In either embodiment, engine noise enters the front volume and is canceled.

Abstract: The susceptibility of an active noise cancellation system to overloading due to very low frequencies is reduced by subtracting the low frequency components of an applied noise field from the residual signal. Low frequency components of the applied noise field outside the normal range of human hearing are detected by an external sensor and isolated by a filter circuit. The isolated low frequency signal is subtracted from the residual signal, resulting in a modified residual signal with reduced low frequency components. The cancellation system thus eliminates very low frequency cancellation signals, without sacrificing bandwidth or system performance within the audible range.

Abstract: Primary vibrations (N), e.g. acoustic noise or vibration from a source thereof such as a motor, are cancelled by secondary vibrations (C) produced by an actuator (2) driven by a controller (3) that is responsive to an error signal (E) detected by a detector (4) and representative of the residual or difference between the primary and secondary vibrations. The controller samples the error signal (E) during successive sampling periods determined by a synchronising signal (syn) taken from the motor. The secondary vibrations C.sub.n+1 for a sampling period n+1 are determined as follows: C.sub.n+1 =C.sub.n -.mu.E.sub.n SGN[1/H], where C.sub.n represents the secondary vibrations produced during a preceding sampling period (n); E.sub.n represents the detected error signal for said preceding period n, H represents the transfer coefficient between the actuator (2) and the detector (4) and .mu. is a scaling factor where 0.ltoreq..mu..ltoreq.1.

Abstract: A control system is described for improving continuous dynamical control on the pressure in the outlet or inlet system (3) or both of a machine (1) in order to control the performance of the machine. The system comprises an actuator (4) for varying the pressure in the selected system, a sensor (8) for monitoring the operation of the machine and producing a signal indicative thereof, and control means (5) responsive to the sensor signals for driving the actuator, wherein the control means operates to adjust the machine performance according to predetermined data, to optimise the machine performance. The data may be in a memory (look-up table) or the control means may operate in accordance with an algorithm.

Abstract: An actively controlled mount system to control vibration which permits static forces from a machine while decoupling the transmission of dynamic vibrational forces. The mount system provides a reduction of force losses from a first generating area to a second force applying area to actively control vibrations of a vibrating element. These force losses are minimized due to minimization of the mass and velocity of fluid pumped by pumping the fluid through short large cross-sectional area passageways. The device provides for channeling of the forces to the vibrating element in a uniaxial direction and constrains the application of forces in non-working directions.

Abstract: A method and system for altering the frequency or harmonic spectra of a disturbance characterized by an output generator (26) and a response generator (24) that cooperate to produce shaped control signals in response to first input signals (23).

Abstract: A method and apparatus is described for actively canceling a primary noise source to produce a desired noise level at at least one location. The apparatus comprises a signal processor which drives at least one actuator, at least one error sensor and a primary noise reference signal. The error sensors are positioned proximate to each of the locations. The output of the error sensors and the primary noise reference signal are sent to the signal processor. The relationship between the driving output of the processor and the output of the error sensors is modeled by a block of filter coefficients. Based upon the model and the primary noise reference signal, the processor drives the actuator to generate a canceling noise at the location. The processor calculates differences between the desired noise level and the output of the sensors. A variable convergence factor and a gradient block are derived from the residual noise and are used to adapt the filter coefficients.

Abstract: Active system for both attenuating mechanical vibration and the noise occasioned by the operation of vibratory feeder bowls in manufacturing having accelerometer (20) adjacent feeder bowl (21) and an inertial actuator (57) and a controller (59) to control both disturbances.

Abstract: A wireless remote active noise canceling headset including residual microphones (35, 34) mounted on the headset (30) with speakers (32, 33) located adjacent to the residual microphones and an algorithm driven synchronous controller to operate said headset.

Abstract: A multiple-input, multiple-output adaptive control system which utilizes perturbations to the frequency components of the outputs to determine the desired changes to said coefficients. The control system is particularly suited to the active control of noise and vibration.