Everything is shrouded in total secrecy: here, in these mysterious rooms, in the utmost privacy, the prototypes of the future are developed, but also the sounds of tomorrow and the connected functions of the cars to come. We are talking about anechoic chambers, isolated from sound and electromagnetic waves, the sancta sanctorum of car manufacturers in terms of design and development.
Now, for the first time, in this case Stéphane Barrelet, Head of the Acoustics and Vibrations Department of the Renault Group, opens the soundproof doors of these temples of silence to us.
In fact, the Renault Group has many testing and engineering infrastructures, in France and around the world. Among these there is one, in Aubevoye in the Eure Department 100 km north-west of Paris, which contains a hidden treasure: the anechoic chambers. Behind its immense gates, the site extends over more than 600 hectares closed to the public and offers, among other things, about 60 km of slopes, 44 test benches, 2 wind tunnels and 18 corrosion test chambers. And it is precisely here, where a thousand specialists work, that there are the famous anechoic chambers: the walls and the ceiling are covered with foam rubber panels on which sometimes horizontal and sometimes vertical prisms rise. These protuberances absorb sound and electromagnetic waves reproducing the conditions of a free field.
“Here – explains Stéphane Barrelet – the term“ silence ”takes on a whole different meaning. Nothing is heard at all, the absence of sound becomes overwhelming. Then we move and the slightest noise, from the rustle of a fabric to the breath, is extraordinarily perceptible, in the absence of parasitic sounds. Instead, a clap of the hands produces a sound that seems muffled, muffled, because the walls do not send back the echo. It is a truly unusual experience ”.
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“We measure – continues the super technician – the vehicle’s insulation level with respect to the noise generated by the engine, tires and any element of the surrounding environment. This is where we work on the acoustic insulation of the vehicle and on the sounds that contribute to the sound experience experienced by the user: door noise, internal acoustic alarms, music, etc. The acoustics experts thus elaborate and measure a complete sound architecture , composed of sounds inside and outside the vehicle “.
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For example, it was here that the French company first developed the Vsp (Vehicle Sound for Pedestrians), a sound made specifically to warn pedestrians of the presence of the Zoe electric car. But this is also where the little noises of electric cars have been revolutionized that have a different click of buttons, turn signals, welcome sounds, ignition of the engine and much more …
On the Renault campus there is also another very special room: it has walls covered with white panels that cover a thick layer of insulating materials. Here the cars are tested on a roller bench that allows you to simulate driving. The vehicle is surrounded by antennas that bombard it with waves of all powers and frequencies. In fact, any vehicle in circulation is constantly subjected to electromagnetic fields, whether it is mobile telephone repeaters, television transmitters or automatic radars. It must therefore be ensured that nothing disturbs the operation of the vehicle. “We are in a Faraday cage. The walls of this chamber retain electromagnetic waves and insulate from the external ecosystem. So we can test the emission and reception performance of the car on a wide range of waves: radio, telephone or GPS.
“If the sound waves around vehicles have decreased – explains Stéphane Barrelet – this is not the case for electromagnetic waves. Since the turn of the century, the number of electronic devices in vehicles has quadrupled. Modern cars, in fact, offer new connected functions and new driving assistance devices. This multi-connectivity increases not only the amount of waves exchanged inside the vehicle, but also outside. It is therefore necessary to ensure that all these frequencies do not conflict, so as not to disturb the functioning of the equipment, of course, but above all so as not to compromise the safety of the vehicle and guarantee safe and reliable cars for all Renault customers ”.