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Safe and sound: The developments in active noise cancelling technology

By / 5 years ago / Features / No Comments

Active noise cancellation is the latest tool in the car industry’s quest to improve refinement and make cars less stressful places to be for company car drivers.

It works on a similar principle to noise cancelling headphones, feeding signals through the stereo to boost or supress certain frequencies.

The physics behind it is actually quite simple. Soundwaves are a series of peaks and troughs; when two peaks collide the overall volume will increase, but if a peak coincides with a trough then the two signals cancel each other out.

Noise cancellation systems use a digital signal processor (DSP) to analyse the unwanted soundwaves and produce a mirror image, matched to the same frequency. They work in much the same way as the noise enhancement systems increasingly found in high performance cars, except here the effect is reversed.

Predictably, it’s a lot harder in practice than it sounds in theory, particularly when you’ve got a whole car to deal with.

For a start, the sound comes from a range of sources, transmitted to various parts of the cabin through a complex network of different paths. As each soundwave travels, the peaks and troughs occur at different points, so without careful design, a system that makes things quieter for the driver could increase noise levels for the passengers.

Likewise, the design needs to be carefully matched to the cabin’s acoustics, otherwise opening a window or folding the rear seats could destroy the benefits.

Engine noise is the easiest to address as the sound can be predicted quite accurately simply by looking at speed and load data from the ECU. In theory, you don’t need any acoustic input at all.

Even so, most manufacturers use microphones strategically placed around the cabin to provide additional monitoring.

Road noise is harder to tackle. Harman is thought to be the only supplier offering this functionality at present, and its system uses a series of accelerometers mounted on the chassis and the suspension to pick up oscillations from the tyres as they’re transmitted through to the cabin. Using this approach the company claims to have achieved peak reductions of up to 10dB for road noise, while evidence suggests as much as 20dB is possible for certain frequencies of engine noise. It’s worth remembering that these reductions apply to specific harmonics, though.

Averaged over the whole frequency range the effect is less pronounced.

As noise cancellation becomes more affordable and more advanced we’re likely to see its use increasing. Audi has employed this technology for several years on its flagship models, while brands like Ford, Infiniti and Fiat- Chrysler are starting to embrace it too.

It’s not simply about comfort, either.

Recent studies suggest that reducing cabin noise delays the onset of driver fatigue, which is the primary cause of around one‐in‐four serious accidents.

What’s more, cancelling out noise electronically could allow manufacturers to reduce weight by shedding a significant amount of sound deadening material – potentially enough to result in tangible benefits to fuel economy and CO2.

It could also help the motor industry address new challenges. One area is to improve the perceived quality of ‘downsized’ two or three cylinder engines, which can sound quite industrial in their natural state. Another is to mask the use of cylinder deactivation – a concept first employed on big V8s and V12s, which is now filtering right down to three cylinder engines. Likewise, it could help to disguise use of the combustion engine on hybrids or rangeextended electric vehicles.

It’s relatively early days at present, and it has to be said some noise‐manipulation systems work better than others. Nonetheless, it presents an intriguing option for car makers facing a rapidly changing world.


In a better place

As well as noise cancellation, other innovations are being combined to help keep drivers safer.

New technology is fundamentally changing the way we spend time in cars, from infotainment systems to control of the vehicle itself.

Perhaps the most far‐reaching implications come from the growing use of mobile internet connections. Streaming music services like Apple CarPlay and Spotify now allow drivers to take their favourite playlists with them from vehicle to vehicle, but that’s just the start. Data from social media and calendar apps will give the car unprecedented access to the driver’s likes and dislikes, allowing it to personalise everything from music selection to route guidance. Always listen to a specific type of music on the way to the gym? Very soon the car will be able to spot where you’re heading and shuffle the media player accordingly.

It’s unlikely that you’ll be able to put your feet up and watch Netflix while this is happening – at least not for the foreseeable future. Nonetheless, manufacturers are looking into ways of helping the driver to do more without distraction. BMW’s Connected Drive system, for instance, will now read text messages and emails aloud, even allowing you to dictate replies.

Beyond that, there’s a whole barrage of technology aimed at helping drivers to relax and destress.

Mood lighting, for instance, helps to tailor the ambience of the cabin by providing subtle areas of illumination, without creating a specific, identifiable light source that might distract the driver.

Air purifiers with user‐selectable scent cartridges aim – quite literally – to improve the atmosphere inside the cabin. The BMW 7‐Series even has an air ioniser; this emits negatively charged ions, which bind onto dust particles and cause them to stick to positively charged surfaces.

It provides an advanced form of air filtration, but there’s evidence to suggest that inhaling negatively charged ions may also improve the body’s ability to absorb oxygen, boosting concentration and alertness. Some scientists even claim it could help fight depression and seasonal affective disorder.

For a more hands‐on approach, an increasing number of manufacturers are turning to massage seats, along with ever more sophisticated heating and ventilation systems within the seat itself.

It might not be long before the driver becomes an integral part of this technology, either. French firm Faurecia has produced a seat that was able to monitor the driver’s heartbeat and breathing patterns using piezoelectric sensors embedded in the seat cushions. From this, it can monitor the driver’s health and stress levels.

In an extreme case, that means a car with an automatic driving function could raise the alarm and bring itself safely to a halt if the driver suffered a heart attack. In day‐to‐day use it would be able to monitor their emotional state and automatically trigger soothing functions like massage seats. That may sound far‐fetched, but Faurecia says this technology could be on the market by 2020.

The impact of these functions may be modest in isolation, but combined they have the potential to make a big difference. The car of the future will be smarter, more efficient and more comfortable and a less stressful environment for company car drivers to spend their time in.

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Alex Grant

Trained on Cardiff University’s renowned Postgraduate Diploma in Motor Magazine Journalism, Alex is an award-winning motoring journalist with ten years’ experience across B2B and consumer titles. A life-long car enthusiast with a fascination for new technology and future drivetrains, he joined Fleet World in April 2011, contributing across the magazine and website portfolio and editing the EV Fleet World Website.