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).