What role will active noise cancellation play in the connected car?

According to a recent research conducted by HARMAN, road noise is the top noise distraction for drivers. An astonishing 55% of respondents in the survey cited this ‘droning’ sound, caused by road noise transmitted through the vehicle structure, as the number one complaint in an environment where they want to enjoy their music.

HARMAN’s survey, conducted in late 2014, also confirmed that car remains the most popular place to listen to music. Of particular interest is the rise among younger age groups enjoying music on the move - over 70% of 18-24 year olds prefer listening to music in the car over anywhere else.

For OEMs, this represents an opportunity to enhance vehicle quality by developing better in-vehicle noise management solutions, whilst giving consumers the best environment to enjoy their music.

The issue of unwanted in-cabin low frequency noise has been exacerbated by changes in vehicle design. Today’s preference for multi-link suspensions, stiff bushings and wide, low profile tyres may improve vehicle dynamics but when combined, they can create multiple noise paths into the cabin.

Sound dampening has drawbacks

The use of sound damping materials to counter this noise and improve in-cabin experience adds weight. As car makers seek to build lighter cars, namely in the quest to meet ever stringent emissions regulations, OEMs are increasingly looking for lighter effective solutions to reduce unwanted in-cabin noise.

Active Noise Cancellation technology or ANC, is one such solution fast gaining ground in the mainstream automotive sector. Unlike passive noise control, which uses sound damping materials as one of the options to isolate vehicle occupants from engine and road noise, ANC works by generating anti-noise similar to the anti-noise created in noise cancellation headphones.

ANC systems such as HALOsonic, a joint development by HARMAN and Lotus Engineering, can now predict and neutralise unwanted in-vehicle low frequency noise. The result is a more comfortable ride, enabling OEMs to use light weight chassis materials thereby reducing fuel consumption and emissions.

Road Noise Cancellation (RNC) – an ANC solution that can effectively minimise road noise – is implemented by placing accelerometers in the path of noise transfer, typically on the suspension and chassis, providing a reference signal to the system controller.

The controller in turn utilises a proprietary algorithm to generate an anti-noise signal that is output through the car's standard loudspeakers. Error microphones in the roof of the car provide adaptive feedback on the cabin noise level in order to fine tune the cancellation, helping occupants enjoy an enhanced driving experience.

Engine-noise cancellation

CES 2015 also saw the presentation of production ready technologies to cancel engine noise in the car cabin. Engine Order Cancellation or EOC, reduces the low frequency drone and rumble emanating from a car engine. Put simply, EOC uses the engine RPM signal as a reference to generate a sound wave that is opposite in phase to the engine induced low frequency noise.

Error microphones mounted in the cabin ceiling provide feedback on the amplitude and phase to refine noise-cancelling effects. Testing suggests a very effective peak noise reduction of up to 20 dB is feasible.

Reducing in-car sound has been a focus for OEMs for some time, but big steps in refinement have been hard to come by. By reducing the low frequency noise in the car cabin, active noise cancellation technology helps OEMs to continue using light weight structural materials thereby reducing fuel consumption and CO2 emissions.

More importantly, the low frequency droning noise in the car cabin increases stress and induces driver drowsiness. By reducing the low frequency noise, ANC technologies helps delay the onset of driver drowsiness, addressing the safety aspect as well.

Thus ANC offers solutions to many of the challenges faced by OEMs and car occupants alike, and the relevance of technologies such as RNC and EOC across a diverse range of vehicles could accelerate their adoption.
As awareness rises for this type of technology, expect to be hearing more – or perhaps less -- in your future car…

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