Wetzlar, Germany - Anybody who’s ever played the guitar as a teenager knows that musical instruments (real ones, that is) function by vibrating the sides of a box. Classical guitarists feel the bass notes produced by their instruments against their ribs, rather than hearing them.

In the same way, a conventional audio speaker works by vibrating the air in a box via a paper cone and an electromagnet - an actuator.

Now Continental has taken that principle one huge step further, with the simple realisation that a sedan car is nothing more than a tin box with a wheel at each corner.

For many years the engineers at Continental have been engaged in the battle to reduce ambient noise inside those boxes by damping out the vibrations in various parts of the structure that are heard as rumbling and road noise - until somebody realised that those vibrations could make music, rather than spoil it, by attaching a flat-mounted actuator (in principle, just an electromagnet and a coil) to a section of the car’s body and using it as a flat-plane speaker, thus creating natural 3D sound without any amplifier tricks. Enter the speakerless car.

The NVH (noise vibration and harshness) engineers were well aware that A pillars are susceptible to high-frequency vibration - so they became the tweeters in the demo car. Door panels are prone to mid-frequency thrumming, so they are now midi-speakers, while the largest surfaces - the roof and boot-lid - are used as woofers. 

The typical audio setup in a car has a number of limiting factors; in order to produce lifelike sound in a car you need as many as 19 speakers, integrated by a remarkably complex sound-mapping amplifier. Each of those speakers has to have a grille, which cramps the style of the interior stylists, and each one needs a box - a totally wasted space - which can amount to 30 litres on a premium audio system, interior volume the boffins would love to be able to use for storage. 

And all that specialised engineering adds about 15 kilograms, to the weight of the cars - a significant penalty at a time when there is huge focus on making cars lighter, not heavier.

So Continental set about re-inventing the audio system, applying the principles embodied in stringed instruments to the surfaces of the car’s interior by means of small coil-and-magnet actuators - in fact, the speakerless system uses less current than a conventional set-up, and it can be integrated into any car body, from a battery powered mini-car to a luxury sedan, at the design stage, at very little extra cost.

Continental’s demo car also demonstrates the scalability of the concept - it can be set up as a low-cost system using three audio channels (and still deliver remarkable sound quality), as a mid-level system with four to six channels and as a high-end system with up to 12 channels for true surround sound, using the seat frames and floor panels as subwoofers, giving rear-seat passengers a whole new audio experience that has won the approval of master violin-makers.

Possible the most startling effect however, is when the system is used for to voice interaction between car and driver; it sounds as if the car itself is talking to you, not its sound system!

IOL Motoring

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