Sound move

Lotus has launched an in-car noise reduction system that generates sound to neutralise engine and road noise via the stereo loudspeakers.

The In-Car Active Acoustic Tailoring (ICAAT) system works by emitting sound waves in the opposing phase to the low-frequency noise entering the cabin.

Engines and aerodynamics have improved over the last decade, but Lotus claims that better car styling and safety has resulted in greater in-car noise from the road surface.

Manufacturers today fit larger wheels made from alloy, with wider tyres, which increases the level of noise from the road. Multi-link suspension rather than standard beam axle also means more vibration and noise can travel through the car.

ICAAT uses four to six accelerometers on the suspension to measure vibration as it comes in from the road, in parallel to data from throttle and engine sensors. Microphones on the interior roof measure the sound pressure conditions in the cabin affected by, say, the number of passengers or temperature.

A processor uses all this data to match the opposing phase output from the loudspeakers, dynamically cancelling out the noise as the engine speed and road surface changes. The key advantage of an active noise suppression system is that it can ‘intelligently’ respond to different noise as it enters the cabin, and also overcome subtly different vehicle builds.

Active engine noise suppression systems have been placed in some Japanese-specification cars since the 1990s, but Lotus claims ICAAT is significantly cheaper and could be introduced in mass-production cars in two to three years.

Steve Kenchington, chief engineer of control systems said that the system targets the difficult-to- block lower range of frequencies.

‘We can cancel up to 400Hz, but the zone of sound reduction gets smaller, so we concentrate on 250Hz down to the lowest range the speakers are capable of; that’s around 40-50Hz in a high-end entertainment system,’ he said.

‘Our active noise system complements passive technology, which tends to run out of steam at frequencies lower than 250Hz.’

Paul Harvey, head of chassis engineering, said that the system allows more design flexibility elsewhere in the car.

‘The engine and exhaust mounting structures within the vehicle for example can be tweaked to reduce noise, but as parts they have to support the structure they’re attached to. If you try to make them softer to reduce vibration transmission, it starts to impinge on their primary role.’