Abstract: A method for designing a frequency periodic filter with a frequency response which has a periodic bandwidth including designing a first sampled data filter whose response corresponds to a set period and replacing each unit sampling delay by a second sampled data filter.

Abstract: An active foam system for noise and vibration control which employs embedded PVDF layers (12) in a urethane foam pad (13). The system can be used to isolate and/or attenuate vibration. It can also be used to cause a reduction in far-field acoustic pressure and to act as a structurally radiated speaker (130).

Abstract: In the area of active noise cancellation headsets, the noisy environment often encountered in the link with communication systems causes lack of intelligibility on the outward communications path. Consequently another in-wire cancellation channel to enhance the intelligibility is required. This additional processing channel adds to the cost of the headset. The invention uses residual microphones (12) to reproduce the sound that remains in the ear after cancellation so that the controller (13) can make further adjustments through filter (15) and LMS adapter (14) to the anti-noise signal.

Abstract: The invention relates to noise or sound control achieved by enclosing the noise source in an active enclosure. Arrays of vibration inputs (for example, shakers, piezoceramics, etc.) are attached to the walls of the active enclosure, or loudspeakers located inside the enclosure can be used to excite the sides of the enclosure. An array of error microphones are located in the radiated acoustic field or PVDF strips are positioned on the wall. A controller senses the levels of sound observed at the error microphones or PVDF film and adjusts the oscillating inputs (in terms of frequency content, phase and magnitude) to the active vibration inputs in order to minimize the radiated sound.

Abstract: A repetitive noise cancellation system for multiple noise sources employing a controller (36) which senses radiated noise by reference sensors (35) and the status of the noise sources by position sensors (37, 38) and automatically controls one of the noise sources so that the noises being emitted from the multiple sources cancel one another.

Abstract: An actuator having a linear current force characteristic comprises a moving coil transducer and a hydraulic lever. The moving coil is capable of producing only a relatively low force but with a relatively large displacement. The coil is formed on a piston which acts as an input piston to a hydraulic level. An output piston has a much larger area than the input piston. Thus, the long throw, low force input to the hydraulic lever is converted into a short throw, high force output at the second piston.

Abstract: An active control system for attenuating tonal noise in a defined region is described. In its most basic form the system includes sensors for generating signals indicative of the residual noise in the region after attenuation and the uncontrolled sound affecting the region, signal processing circuit for processing the generated signals differently depending on the tonal content thereof, an adaptive filter supplied with at least one of the generated signals whose characteristic is controlled by the processing circuitry, a transducer for producing tonal-noise-attenuating disturbance in the region and delay means for delaying signals relating to the uncontrolled noise before or after or during the adaptive filtering. The system finds direct application in a personal headset or ear defender.

Abstract: A filter system with low throughput delay having at least two parallel filters, either sampled-data or continuous, wherein one of the filters has a low throughput delay in comparison with the other filters.

Abstract: A vibration control system includes a processor-based circuit which monitors and controls an analog vibration control circuit. The system includes a sensor to detect the undesirable vibrations and a synchronous pulse generator for determining the fundamental frequency of the vibrations emitted by the source. An actuator produces anti-noise to counter unwanted vibrations. The processor circuit tests the system, monitors system functions, and adjusts various parameters to provide optimal performance.

Abstract: A control system for controlling periodic disturbances employing a delayed inverse filter (5), a variable delay (6), a controller, a system model (4) and a comb filter (9).

Abstract: A system for reducing periodic noise, which includes a plurality of harmonically related noise signals, comprises an actuator for producing a canceling acoustic signal, a sensor for detecting a residual noise signal, a synchronizing signal generator and processing circuitry. The processing circuitry comprises a plurality of tunable harmonically related band pass filters, a tuning signal generator and a summer which sums the outputs of the filters. The tuning signal generator receives the synchronizing signal from the synchronizing signal generator and outputs the tuning signals to the band pass filters. As the frequency of the synchronizing signal changes, the tuning signal generator causes the tunable filters to track harmonics of the noise to be canceled. After summing by the summer and suitable amplification, the outputs from the filters are used to drive the actuator so as to reduce the residual noise detected by the sensor.

Abstract: This application outlines several applications of a piezoelectric materials invention to produce quality loudspeakers in applications where coil driven dynamic speakers are difficult or impossible to implement with an appreciable degree of sound quality. This invention includes a series of modifications to a laptop computer such as the IBM 750c. The modifications to the computer consist of placing piezoelectric patches behind the LCD and directly to the back wall of the laptop lid. Damping materials and stiffeners are also added to the back wall to reduce structural resonance. A system consisting of an audio amplifier and transformer is used to drive the piezo speaker.

Abstract: A simple, low cost active noise cancellation system employing a delay and actuator estimator (35), a gain determination (34), a gain (33) and speaker (36) that cancels stationary random noise such as that encountered on a rangehood fan.

Abstract: This invention relates to control systems for the control of noise and vibration. Resonators with adjustable properties are used in conjunction with an electronic control system to change the noise or vibration in a structure. The invention relates particularly to the control of quasi-periodic noise or vibration comprising one or more harmonics by using one or more adaptive resonators.

Abstract: A muffler for muffling noise in a fluid flow, such as exhaust gases from an internal combustion engine comprises a chamber, loudspeakers for injecting anti-noise into the chamber under the control of processing circuitry in dependence upon residual noise detected by a microphone. The gas flows from an inflow pipe to an outflow pipe past a radial aperture that produces an acoustic coupling between the chamber and the gas flow, to allow the anti-noise to mix with noise in the gas flow and produce noise cancellation. The coupling is so arranged that the chamber becomes pressurized by the gas flow, in use, so as to restrict hot gas flow through the chamber and thereby provide an essentially benign environment for the loudspeaker.

Abstract: The present invention relates generally to global noise or sound control and, more particularly, to the control or sound radiated from stationary induction apparatus such as power transformers and shunt reactors by use of active enclosures and active panels. The purpose of the invention is to markedly reduce the radiation of sound from the machine to all observation points in the surrounding field with a very lightweight, compact, non-airtight structure which does not impair maintenance or repair of the machine.

Abstract: This invention relates to the various features of a headset design that utilizes active noise cancellation. This particular design has been developed to work with radio communication systems, but many features are applicable to headsets designed solely for ear protection. The unique design features of the invention allow for uninterrupted communication capability with active noise cancellation. The design also provides it own built in rechargeable power supply that is easily removed for recharging.

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 and vibration reduction system for canceling noise in aircraft or other passenger carrying transportation systems which utilizes a series of seat mounted microphones and trim mounted speakers in conjunction with a digital controller with a class-D stage power amplifier and which is synched to the aircraft alternator.

Abstract: An adaptive canceller filter module having signal sensors and signal filters in a circuit for use with filtered-x algorithms to adapt the coefficients of one of said filters to minimize the measure of the error.