Active Exhaust Noise Cancellation

Basic Description

All vehicles with an internal combustion engine have a muffler located along the exhaust pipe that helps to reduce the acoustic noise emitted by the engine. Most mufflers are passive devices that route the exhaust gasses through chambers and perforated tubes in order to filter the acoustic frequency vibrations without obstructing the flow of the gases significantly. Active sound cancellation systems use one or more vibrating panels (essentially speakers) driven by a microprocessor. The microprocessor monitors the engine operation and/or the the acoustic frequencies propagating in the exhaust pipe and generates sound that is out-of-phase with the noise generated by the engine.

The principle is similar to that used by noise-canceling headphones only the "speakers" used in automotive exhaust systems must be more powerful and capable of withstanding the intense heat and corrosive environment of an automobile exhaust. Active sound cancellation systems can also be used to change the sound of an automobile's engine, making a small engine sound more powerful or a diesel engine sound like a gasoline engine.

Sensors

microphone and/or connection to the engine control module

Actuators

rugged high-temperature speakers

Data Communications

Typically CAN

Manufacturers

none currently

For More Information

[1] Active Noise Control, Wikipedia

[2] Making Tailpipe Music, Automotive Engineering International Online, August 18, 2009.

[3] Active Exhaust Silencer, U.S. Patent Number 5,541,373, July 30, 1996.