Abstract: An adaptive control system that can be used for active acoustic attenuation implements an LMS or an RLMS update using an error signal that is filtered through a delayed Hermitian transpose of a C model of an auxiliary path following an adaptive control filter. Adaptive on-line C modeling can be used effectively. The invention is useful in SISO and MIMO applications, and can reduce the number of filtering operations in systems using several reference signals. The invention does not require inverse C modeling.

Abstract: An active adaptive control system introduces a control signal from an output transducer (14) to combine with the system input signal (6) and yield a system output signal (8). An error transducer (16) senses the system output signal and provides an error signal (44). An adaptive filter model (40) has a model input from a reference signal (42) correlated to the system input signal, and an output outputting a correction signal (46) to the output transducer to introduce the control signal according to a weight update signal (74) provided by the product (from multiplier 72) of the reference signal and the error signal. Selective leakage of the weight update signal is provided in response to a given condition of a given parameter, preferably output power of the correction signal, to control performance of the model, to selectively degrade same according to need. Leakage is varied by multiplying a previous weight update value by a factor .gamma.

Abstract: An act control system introduces a control signal put transducer (14) to combine with the system input signal (6) and yield a system output signal (8). An adaptive filter model (40) has an output (46) supplying a correction signal to the output transducer to introduce the control signal. The model has a first error input (44, 232, 248) driven by an error signal from an error transducer (16) to drive the correction signal toward a value matching the system input signal to modify and/or cancel same. The model has a second error input (202, 224, 240, 268, 280) selectively driven by a spectral leak signal (212) to drive the correction signal away from such matching value by driving the correction signal towards zero, to selectively constrain performance of the model in response to a given condition of a given parameter.

Abstract: An adaptive multi-channel active acoustic attenuation system is provided for attenuating complex acoustic waves. The system includes a plurality of input sensor nodes and a plurality of error sensor nodes. Each node includes a central processing unit and a network interface. A medium physically interconnects each of the network interfaces to a communication module of a controller by means of a control bus or the like. A control network is provided for controlling communication between a communication module of a controller and each of the network interfaces to control the flow of data along the medium.

Abstract: Using a set of basis vectors, output from an adaptive control filter or adaptation of the control filter can be selectively constrained. Selected basis vectors define an adaptation subspace. The adaptive control filter can have a bank of non-adaptive FIR filters and a linear combiner with adaptive weights and fixed weights, or can use projection methods in conjunction with conventional adaptive FIR or IIR filter models. Filtered-X and filtered-U techniques can also be used.

Abstract: A multi-filter-set active adaptive control system includes a plurality of output transducer arrays introducing control signals to combine with a system input signal to yield a system output signal. A plurality of error transducers sense the system output signal and provide a plurality of error signals to a plurality of sets of adaptive filters. A plurality of sets of D/A converters are provided at the outputs of the adaptive filters outputting correction signals therethrough. A plurality of sets of A/D converters are provided at the filter inputs and error inputs of the adaptive filters. Various filter sets and combinations are provided.

Abstract: An active silencer for a vehicle exhaust system that has a low profile so that it can be hung underneath the vehicle in a conventional manner without altering the vehicle. The silencer has a chamber isolated from the exhaust flow in which one or more speakers are mounted side-by-side. The speakers face downwards and share a common tuning chamber within the isolated chamber. The tuning chamber is ported to a mixing chamber where the canceling acoustic waves mix with noise from the exhaust flow before the exhaust noise exits to the atmosphere.

Abstract: An integral active and passive silencer particularly useful for industrial applications. The integral unit is easy to install, disassemble and service. It provides a housing that can be separated into portions, with each portion containing an active or passive silencer. The invention also provides an active silencer having a ported tube that is in acoustic communication with one or more loudspeakers through a tuning chamber. The ported tube can be removable.

Abstract: An active noise control system is provided for cancellation of noise in a duct. A speaker is mounted over an opening in the duct. An enclosure is mounted the duct about the speaker. Air flow is generated through the enclosure in order to balance the diffusion of water vapor through the speaker such that the dew point of the air in the enclosure is always below the temperature of the air in the enclosure, thus avoiding condensation.

Abstract: An active acoustic attenuation system and method which operates in a waveguide (i.e. duct or beam) to attenuate acoustic waves having energy in the plane wave node and in higher order nodes. The invention does this by sensing the acoustic wave at linearly independent locations across a waveguide, decoupling the signals to generate an independent signal for each node being attenuated, processing the signal for each node independently of one another, and combining the processed signals for each node to drive a set of actuators at linearly independent locations across a waveguide. The invention is useful for both sound control and vibration control.

Abstract: An active attenuation system has indirect error sensing. The invention operates in systems which attenuate an acoustic wave after the acoustic wave has propagated through and exited from a waveguide. Indirect error sensing is done by sensing the primary acoustic wave which is being attenuated while it is propagating through the waveguide, measuring a canceling acoustic wave while it is propagating in another waveguide, and by combining the measurements to generate an error signal corresponding to the error after the primary and canceling acoustic waves have combined in free space. Thus error measurements can be made without having exposed error sensors.

Abstract: An acoustic system (20) includes a model reference (22) having a selectably programmable response, and an active model (24) including in combination an acoustic path (26) and an adaptive filter (28) such that the combination of the acoustic path (26) and the adaptive filter (28) adaptively models the model reference (22) such that the combined response of the acoustic path (26) and the adaptive filter (28) provides an active model response matching the response of the model reference (22).