Abstract: A lubricant filtering and monitoring system and method is provided for a lubricant circulation system circulating lubricant through a filter to a lubricated component. A combination of sensors senses a condition of the lubricant before and after passage through the filter and before and after passage through the component and provides an output indicative of a condition in the circulation system. A sensor senses a condition of lubricant flowing through the filter, and another sensor senses a condition of lubricant flowing through a reference section for comparison against and normalizing of the output of the first sensor. A method of actively monitoring the component is provided by comparing influent to the component with effluent from the component to ascertain how lubricant is being modified by the component, by sensing a condition of lubricant passing through the filter. An effective method is provided for determining when to change or clean the filter.

Abstract: An acoustic resonator (20) has a resonator cavity (22) with a resonator port (24) for communicating with an exhaust flow passage (26) conducting acoustic waves therethrough. Adjustable port structure varies acoustic impedance of the port by various combinations including translation to vary area along an arcuate surface, translation between discrete areas, translation to cumulatively open port area, multiple translation, multiple ports, rotational area change, and rotational length change. Adaptive control may be provided. A combined passive and active acoustic system may also be provided.

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. Performance of the model is selectively controlled to control the signal sent to the output transducer. Various monitoring and control methods are provided, including spectral leak signal monitoring and control, correction signal monitoring and control, frequency responsive spectral transfer function processing of the leak signal and/or the correction signal, reference signal processing, and fuzzy logic control.

Abstract: A system that facilitates the development and operation of active sound or vibration control systems, especially for those not skilled in computer programming. The system facilitates the development of developing active sound or vibration control systems implementing an adaptive control model. In particular, the system has a software collection containing control system software that implements an adaptive control model which can be programmed on an electronic controller to actively control sound or vibration. The system also has a user interface that prompts the user to enter information pertaining to the control system being developed so that the electronic controller can implement an adaptive control model in accordance with the information entered by the user.

Abstract: A multi-channel communication system is provided. In an active acoustic attenuation implementation, noise, including cross-coupled noise between channels and locations, designated audio signals, and echoes, are canceled, but not speech from another location. A particularly desirable vehicle application is provided.

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: 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 active acoustic attenuation system attenuates a correlated input acoustic wave and eliminates the need for an input transducer sensing such wave. An output transducer introduces a canceling acoustic wave to attenuate the input acoustic wave and yield an attenuated output acoustic wave. An error transducer senses the output acoustic wave and provides an error signal. An adaptive filter model has a model input, a model output outputting a correction signal to the output transducer to introduce the canceling acoustic wave and an error input from the error transducer. A summer has a first input from the model output, a second input from the error transducer, and an output outputting a resultant sum to the model input, such that the model input is provided by the sum of the correction signal and the error signal.

Abstract: An active acoustic attenuation system specifies the error signal (44) to correspondingly specify the output acoustic wave. In the preferred embodiment, the error signal (44) is specified by summing (210) the error signal (44) with a desired signal (204) to provide a specified error signal (206) to the error input (202) of the adaptive filter model (40) such that the model (40) outputs the correction signal (46) to the output transducer (14) to introduce the canceling acoustic wave which specifies the output acoustic wave such that a desired signal is present in the output acoustic wave.

Abstract: An acoustic system has a chamber (12) having an input (14) for receiving an input acoustic wave and guiding the input acoustic wave along a flowpath (16) to a chamber output (18), an acoustic transducer (20, 22, 24) interacting with the acoustic wave in the chamber (12), and a venturi (30, 32, 34) drawing air into the flowpath (16) to flow to the chamber output (18). The venturi aspirates internal areas of the chamber to keep the acoustic transducers clean and/or aspirates external air into the chamber past the transducers to cool same.

Abstract: An active acoustic attenuation system (10) is provided with various adaptive filter models (40, 48, 56, 70, 84, 100) enabling communication between persons (26, 30) in spaced zones (12, 16) by selectively cancelling undesired noise and undesired speech, all on an on-line basis without dedicated off-line pretraining and also for both broadband and narrowband noise.

Abstract: A method is provided for reducing convergence time of an active acoustic attenuation system upon start-up or upon a given sensed parameter change. The weights of the adaptive filter model coefficient weight vector are started at or changed to values which are closer to the converged value than the initial or present nonconverged value is to the converged value. The filter model converges in a shorter time as the weights change and are updated from their starting or changed value to the converged value.

Abstract: An active acoustic attenuation system (200) has a first adaptive filter model M modeling the acoustic path P from an input transducer (10) to an output transducer (14), and a second adaptive filter model Q modeling the overall system from the input transducer (10) to an error transducer (16). A third adaptive filter model T models the transfer function S of the output transducer (14) and the error path E between the output transducer (14) and the error transducer (16), without an auxiliary random noise source.

Abstract: A microphone probe for acoustic measurement in turbulent flow. The probe includes a tube having a closed end facing upstream with respect to the direction of sound propagation and a microphone is located in a downstream end of the tube. At least a portion of the length of the tube is composed of a rigid foraminous material containing a multiplicity of interconnected cells with the average cell size being less than 100 microns. In operation sound pressure fluctuations cause pressure waves to propagate through the cells to the inside of the tube and the sound pressure waves add constructively to create a high pressure sound at the microphone, while turbulent flow pressure fluctuations are essentially averaged out.

Abstract: A system is provided for increasing the frequency range of an active acoustic attenuation system in a duct without increasing cut-off frequency f.sub.c of the duct or otherwise splitting or partitioning the duct into separate ducts or chambers. The frequency range is increased above f.sub.c to include higher order modes. A plurality of cancelling model sets are provided. Each transverse portion of the acoustic pressure wave has its own set of an adaptive filter model, cancelling speaker, and error microphone. A single input microphone may service all sets.

Abstract: A microphone probe for acoustic measurement in turbulent flow. The probe includes a tube having a closed end facing upstream with respect to the direction of sound propagation, and a microphone is located in the downstream end of the tube. The tube is provided with a plurality of small ports, or alternately a slit, that extend a substantial portion of the length of the tube and an acoustically resistive material is stretched across the ports and clamped to the tube. In one form of the invention, the side edges of the material are connected to rigid bars and the bars are drawn together by a plurality of threaded fasteners to stretch the material over the ports. The threaded adjustment of the fasteners provides a means for varying the acoustical resistance of the material. In a second form of the invention, the bars to which the side edges of the material are attached, are clamped together by spring clips.

Abstract: An active acoustic attenuation system is provided that actively models direct and feedback paths as well as characteristics of the secondary cancelling sound source and the error path on an on-line basis. The primary model uses a recursive least mean squares RLMS algorithm that is excited by the input acoustic noise and uses the residual acoustic noise as an error signal. The secondary sound source or cancelling speaker and the error path are modeled by a second algorithm, particularly an LMS algorithm, that uses an additional auxiliary low level, random, uncorrelated noise source as an input signal. The resulting overall system provides excellent attenuation of narrow band and broad band noise over a relatively wide frequency range on a completely adaptive basis without directional transducers.

Abstract: An active acoustic attenuation system (2) is provided for attenuating an undesirable output acoustic wave by introducing a cancelling acoustic wave from an omnidirectional speaker (14) at the output (8), and for adaptively compensating for feedback from the speaker (14) to the input (6) for both broad band and narrow band acoustic waves, without pre-training. The feedback path (20) is modeled with a single filter model (40) adaptively modeling the acoustic system (4) on-line without dedicated off-line pre-training, and also adaptively modeling the feedback path (20) from the speaker (14) to the input microphone (10) on-line for both broad band and narrow band acoustic waves without dedicated off-line pre-training, and outputting a correction signal to the speaker (14) to introduce a cancelling acoustic wave.

Abstract: Acoustic attenuation apparatus (2) is provided for a duct (4) guiding an acoustic wave propagating (6) therethrough. A silencer (8) is provided for passively attenuating the acoustic wave in the duct, and a cancelling speaker (32) is provided within the silencer. The combination provides hybrid active/passive combined attenuation. Various rectangular and circular structures are disclosed, together with multi-path and multi-speaker arrangements.

Abstract: A muffler construction comprising an outer body, and a pair of end walls extend transversely across the body to define an internal chamber. An inlet conduit is located in one of the end walls, while an outlet conduit is in the other end wall. In one embodiment, the inlet conduit is disposed axially of the body to excite symmetric higher order modes and the outlet is offset radially from the axis of the body and is located on a nodal circle of the transverse pressure distribution. In a second embodiment, the inlet is offset from the axis of the body causing excitation of asymmetric higher order modes and the outlet is located on a nodal line of the transverse pressure distribution. The construction of the invention maximizes attenuation of high order modes in mufflers.