Automotive Electronics Banner

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 gases 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 acoustic frequencies propagating in the exhaust pipe and generates sound that is out-of-phase with the noise generated by the engine.

Block diagram of exhaust noise cancelation

The principle is similar to that used by noise-canceling headphones only the microphones and 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.

Block diagram of exhaust noise cancelation

Another advantage of active noise cancellation exhausts is that they are relatively light and compact compared to passive mufflers, and can help to reduce the weight of the vehicle. They also can help reduce the length of the exhaust pipe, saving additional weight and material costs.

Active exhaust noise cancellation is rare in cars today, but several manufacturers offer "Active Exhaust" systems. These systems do not attempt to actively cancel exhaust noise. Instead, they use electronically controlled valves to redirect exhaust through different paths in the exhaust system causing the exhaust noise to have a different tone and/or amplitude.

Microphone and/or connection to the engine control module
Rugged high-temperature speakers
Data Communications
Typically CAN
For More Information
[1] Active Noise Control, Wikipedia.
[2] Making Tailpipe Music, Automotive Engineering International Online, Aug. 18, 2009.
[3] Active Exhaust Silencer, U.S. Patent Number 5,541,373, July 30, 1996.
[4] Active Noise Cancellation Applied to Diesel Exhaust, Christoph Hammerschmidt, EE Times, Oct. 20, 2010.
[5] Jaguar F-Type V6 Active Exhaust On & Off, YouTube, Sep. 13, 2013.
[6] Video: Z51 Active Exhaust System on 2014 Corvette Stingray,, Oct. 15, 2013.
[7] BMW F10 F11 535D + Active Sound Exhaust System, YouTube, Nov. 3, 2014.