The secret of the anechoic chambers where future vehicles are tested

Every morning, Stéphane travels the Norman country roads where only the song of a few early birds breaks the silence and heralds the awakening of nature.

The secret of the anechoic chambers where future vehicles are tested

Every morning, Stéphane travels the Norman country roads where only the song of a few early birds breaks the silence and heralds the awakening of nature. Very soon, calm gives way to bustling activity at the Aubevoye Technical Center, a Renault engineering and testing complex located 100 kilometers northeast of Paris. Behind imposing gates, the center extends over more than 600 hectares and houses, among other things, nearly 60 kilometers of tracks, 44 test benches, 2 climatic tunnels and 18 corrosion chambers. All these facilities, hidden by the forest, are intended to test future vehicles of the Renault Group brands in any situation.

Stéphane goes through the successive fences and security gates under the watchful eye of the security agents and enters the center where a thousand specialists work, including engineers, technicians, pilots and experts of all kinds. Let's walk with Stéphane through the labyrinth of corridors of this venue at the forefront of technology that in no way resembles a classic office...

“The new acoustic experience is underway. It must translate into a range of new hearing experiences: outstanding audio quality and more innovative services," explains Stéphane, Head of the Renault Group Acoustics and Vibrations Service.

The walls and ceiling of the first room are covered in foam panels from which horizontal and vertical prisms emerge. These bumps absorb sound and electromagnetic waves reproducing the conditions of a free field, where there is no echo. This is why the room is called "anechoic". "Since the ground is not covered, we speak more of a semi-anechoic chamber", explains Stéphane.

Here, the word "silence" takes on a new meaning. Nothing is really heard and the absence of sound becomes overwhelming. If we move, the slightest noise such as the brush of a cloth or a breath, is perceived in a surprising way in the absence of any parasitic sound. On the contrary, if the palms collide, only a dull, weak sound is heard, since the walls do not return any echo. Stéphane smiles: “it is a truly unique experience!”

In the center of the room and surrounded by a hundred high-quality microphones, a 100% electric New Megane E-TECH copy captures the attention of the test technicians. "We measure the insulation of the car with respect to the noise generated by the engine, the tires or any element in the environment," explains Stéphane. "This is where we work on the sound insulation of the vehicle and the sounds that contribute to the user's acoustic experience: door noise, interior sound alerts, music, etc." This is how acousticians build and measure a complete sound architecture made up of sounds, both inside and outside.

Renault Zoe, pioneer of electric driving ten years ago, had raised new questions about sound and what to do with this silence. Renault had to develop, in these anechoic chambers, a VSP (Vehicle Sound for Pedestrians) so that pedestrians could hear Zoe arrive at low speed. "Imagining a car playing the traviata or a Wagner work is tempting, but we would risk invading the streets with cacophonies," jokes Stéphane. Even so, the 100% electric New Megane E-TECH has several warning sounds for pedestrians.

In the cabin, the disappearance of the purr of the engine has freed up a sound space that should not be ignored: “More attention is now being paid to the sound of the indicators, the jingle of the buttons and the loudness of the interfaces. The driver and the passengers of it are immersed in an acoustic and sensory experience that is part of the trip ».

Not far from there, another special camera catches the eye. Xavier, an expert in electromagnetic compatibility, works there. The walls of this room are covered in white panels that cover a thick layer of insulating materials. There is another 100% electric New Megane E-TECH to be tested on a roller bench that simulates a driving situation. Some antennas surround the car and bombard it with waves of all powers and frequencies. In fact, a vehicle in circulation is constantly subjected to electromagnetic fields, both when approaching any type of antenna, emitters or radars, and it must be ensured that nothing alters the operation of the vehicle. “We are in a Faraday chamber. The walls of this room retain electromagnetic waves and isolate us from the outside ecosystem. In this way, we can test the emission and reception performance of the car in a wide range of waves: radio, telephone or GPS”, explains Xavier.

While sound waves around vehicles have decreased, this is not the case for electromagnetic waves. Since the turn of the century, the number of electronic equipment on board has quadrupled. The 100% electric Renault Megane E-TECH thus proposes new connected functions and new driving aids. This connectivity not only increases the amount of waves that are exchanged inside the car, but also with the outside. Therefore, it is necessary to ensure that all these frequencies do not conflict, so as not to alter the operation of the equipment, of course, but above all so as not to disturb the safety around the vehicle and to guarantee safe and reliable cars for all Renault customers.

On that day, the new flagship of the Renault range and its equipment are subjected to multiple tests, with a level of demand twice higher than that required by regulations. From the control room, each response, each behavior is studied. Everything is examined and analyzed thanks to powerful computers. There should be no question of ensuring the effectiveness and reliability of connected car systems.

Stéphane takes us to a last room. "The show begins..." he warns as he pushes open the heavy door. And it is not for less: the room measures about 300 square meters and 11 meters high. The walls, floor, and ceiling are covered in large foam cones. It is the only fully anechoic chamber in the Aubevoye Technical Center where experts test the wave reception of all vehicles, from Zoe to Master.

The various anechoic chambers and analysis laboratories scattered throughout the labyrinthine Aubevoye Technical Center host a cumulative total of more than a thousand test sessions each year. For long months before they are revealed, and even before they have a name, future Renault vehicles spend whole days in these deaf and blind rooms, surrounded by invisible frequencies. You see nothing, you hear nothing in anechoic chambers, but the stakes are high in these little-known treasures of wave technology.

In the afternoon, when the light dims around Aubevoye, Stéphane leaves his peculiar office. On his drive home through the Norman woods, he rolls down the window and lets the sounds of nature drift on board.


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