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Active Cabin Noise Suppression

Basic Description

Most vehicles with an internal combustion engine utilize materials and passenger compartment designs that help to isolate the vehicle occupants from engine and road noise. Sound damping materials can be heavy and expensive though, providing an incentive to find other ways of reducing cabin noise. A few vehicles employ systems that actively generate an "anti-noise" signal inside the cabin using one or more strategically placed speakers driven by a microprocessor. These systems monitor the noise inside the vehicle using microphones and attempt to cancel the noise by generating an identical signal that is 180 degrees out-of-phase with the detected signal.

The principle is similar to that used by noise-canceling headphones only the volume in which the noise must be canceled is much larger. This makes it very difficult to cancel the noise uniformly throughout the cabin at frequencies above a few hundred hertz.

Illustration of Active Noise Control in an Automobile Passenger Compartment

Systems available today are typically capable of reducing steady state noise (e.g. road and engine noise) at frequencies up to a few hundred hertz by 5 to 10 dB. Similar systems can be attached to the intake manifold or placed in the exhaust system. While not inside the car, these systems can significantly reduce engine and exhaust noise, making the car quieter inside and out. Currently, vehicles have separate active noise cancellation modules, but this function is likely to be integrated into the ECM in the near future, making the systems cheaper and easier to implement.

Some vehicles are now equipped with cylinder deactivation systems that shut down some of the cylinders at cruising speeds. As a result, the engine can produce some strange sounding low-end noises. Active noise suppression is sometimes used to eliminate this undesired sound.

Microphones, accelerometers
Data Communications
Bose, Etrema, Harman, Honda, Mentor Graphics, QNX, Silentium
For More Information
[1] Active Noise Control, Wikipedia.
[2] GMC Terrain - Active Noise Control (ANC) system, YouTube, Feb. 12, 2010.
[3] Automakers Shush Cars with Noise Cancellation Technology, Chris Woodyard, USA Today, Sep. 26, 2012.
[4] Cadillac ELR Active Noise Canceling, YouTube, Oct. 18, 2013.
[5] Bose to Offer Noise Canceling Chips for Vehicles without Bose Systems, Matthew Sitachitt, CarVerse, Jan. 7, 2014.
[6] Product How-To: Active Noise Control - a Software-Based Approach for Automobiles, Tina Jeffrey, EDN Network, Feb. 20, 2014.
[7] HALOsonic Road Noise Cancellation Solution, YouTube, Oct. 27, 2014.
[8] Harman Cancels Out Road Noise, Without Headphones, Philip E. Ross, IEEE Spectrum, Oct. 30, 2014.
[9] Jeep Grand Cherokee Platinum First Drive - Active Noise Cancellation Review, YouTube, Jan. 18, 2015.
[10] Mitsubishi Quiets Car Noise With Machine Learning, IEEE Spectrum, Mar. 9, 2015.