Active Noise Cancellation System Research Articles

Active noise cancellation system

An active noise cancellation system, comprising a circuit for generating one or more reference signals (x(n)) proportional to the noise in the target area, several electronic circuits (1) having adjustable transfer functions (W), such as adaptive filters, adapted to receive the one or more reference signals (x(n)) and to generate noise cancellation signals (y(1,n)), sound sources (2) adapted to receive the noise cancellation signals (y(1,n)) and to generate cancellation noise in the target area for at least partial cancellation of the noise present therein, sensors (3) for detecting residual noise in the target area and converting it to electrical residual noise signals (e(m,n)), transmission path (4) having the estimated transfer function (C') of the transmission path between the electronic circuit (1) and the sensors (3) adapted to receive the one or more reference signals (x(n)), and tuning circuit (5) adapted to receive the residual noise signals (e(m,n)) and output signals from the transmission path circuit (4) and to generate tuning signals (w) and transmit them to the electronic circuit (1) for tuning the transfer functions (W) thereof, and second tuning circuit (6) adapted to receive both the cancellation noise signals (y(1,n)) and the residual noise signals (e(m,n)) and to generate second tuning signals (c) and transmit them to the transmission path circuit (4) for tuning the transfer functions (C') thereof.

Active noise control using noise source having adaptive resonant frequency tuning through variable ring loading

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of noise radiating structure is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating structure is tuned by a plurality of drivers arranged to contact the noise radiating structure. Excitation of the drivers causes expansion or contraction of the drivers, thereby varying the edge loading applied to the noise radiating structure. The drivers are actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the drivers, causing them to expand or contract. The noise radiating structure may be either the outer shroud of the engine or a ring mounted flush with an inner wall of the shroud or disposed in the interior of the shroud.

Active noise control using noise source having adaptive resonant frequency tuning through stress variation

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

Active noise control using noise source having adaptive resonant frequency tuning through variable panel loading

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency is tuned by adjusting the size of a frame which encloses the noise radiating element. One or more expandable elements are disposed in the frame to produce expansion and contraction of the frame. The elements are actuated by a controller which receives input of a feedback signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the frame to expand or contract.

Transducer flux optimization

A transducer for use in an active noise cancellation system is particularly adapted for use as a motor vehicle exhaust muffler by physically designing the transducer to optimize magnetic flux with increases in temperature through the operating temperature range of the motor vehicle. The magnet material used to form the transducer is selected, and the load line which provides increased flux with increases in temperature is then equated to the ratio of the area of the gap to the length of the gap between the magnetic poles divided by the ratio of the area of the magnet to the length of the magnet; by equating the area of the gap to the length of the gap ratios at maximum B/H and the selected load range, the desired length of the magnet is derived since the area of the magnet is determined according to conventional criteria.

Wide-area adaptive active noise cancellation

This paper describes an adaptive active noise cancellation (ANC) system that is based on an output-whitening approach and is an extension of the work of Graupe and Efron on single point adaptive ANC. The controller works by continually estimating the time-series parameters of the noise to be cancelled and by forcing the cancellation network to follow the identified parameters, so that the output is whitened. To address the problem of wide-area cancellation, a system that consists of a weighted array of single point output-whitening cancellation systems is proposed. Each controller is chosen to cancel the local temporal effects of the noise, and the array weights are chosen to match the wavefront shape. A comparison of cancellations based on single-point and wide-area systems demonstrates the superiority of the wide-area system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Stable Method for Active Cancellation of Duct Noise by Synthesized Sound

This paper describes an active noise cancellation system utilizing computer-synthesized sound. This computer-synthesized sound is generated by using a new method to estimate the impulse response of a system involving inverse transfer function of a loudspeaker. A loudspeaker is set close to the end of a duct to radiate sound for cancellation. The loudspeaker is driven by a signal which is synthesized by convoluting the estimated impulse response and the wave form of a noise picked up by a microphone set in the duct. The system is substantially stable. In our experiment, using a duct 8.5 m in length, the sound pressure at a point outside the duct is decreased by about 3 to 8 dB over a frequency range between 50 Hz and 200 Hz.