The secret of the anechoic chambers where future vehicles are tested


Every morning Stéphane travels the Normandy country roads where only the song of a few early risers breaks the silence and announces the awakening of nature. Calm soon gives way to activity in the Aubevoye Technical Center, a Renault engineering and test complex located 100 kilometers northeast of Paris. Behind imposing gates, the center extends over more than 600 hectares and houses, among other things, almost 60 kilometers of tracks, 44 test benches, 2 climate 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 crosses the successive gates and security gates under the watchful eye of the security officers 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 maze of corridors of this location at the forefront of technology that in no way resembles a classic office…

“The new acoustic experience is in full swing. It should translate into a series of new listening experiences: excellent sound 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 with foam panels from which horizontal and vertical prisms emerge. These pulses absorb sound and electromagnetic waves and reproduce the conditions of a free field, where there is no echo. This is why the room is called “anechoic”. “Because 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. When we move, the slightest sound, such as the brush of a cloth or a breath, is perceived in a surprising way without any parasitic noise. On the contrary, when the palms collide, only a dull, faint sound is heard, because the walls do not return an echo. Stéphane laughs: “it’s a really unique experience!”

In the middle of the room and surrounded by a hundred high-quality microphones, a 100% electric New Megane E-TECH copy caught the attention of the test technicians. “We measure the insulation of the car in relation to the noise generated by the engine, the tires or any other element in the environment,” explains Stéphane. “Here we work on the sound insulation of the vehicle and the sounds that contribute to the acoustic experience of the user: door noise, interior noise warnings, music, etc.” In this way, acousticians build and measure a complete sound architecture consisting of sounds, both inside and outside.

Renault Zoe, a pioneer of electric driving ten years ago, had raised new questions about noise and what to do with this silence. Renault had to develop a VSP (Vehicle Sound for Pedestrians) in these anechoic chambers so that pedestrians could hear Zoe approaching at low speed. “It’s tempting to imagine a car playing the traviata or a work by Wagner, but we’d risk invading the streets with cacophones,” Stéphane jokes. Nevertheless, the 100% electric New Megane E-TECH emits several warning sounds for pedestrians.

In the cab, the disappearance of the engine purr has opened up a space of noise that should not be ignored: “More attention is now being paid to the sound of the direction indicators, the ringing of the buttons and the loudness of the interfaces. The driver and his passengers are immersed in an acoustic and sensory experience that is part of the journey.

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 with white panels that cover a thick layer of insulating material. There is still a 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 exposed to electromagnetic fields, whether approaching any type of antenna, transmitters or radars, and care must be taken that nothing alters the operation of the vehicle. “We are in a Faraday room. The walls of this room trap electromagnetic waves and isolate us from the external 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, so have electromagnetic waves. Since the turn of the century, the number of electronic equipment on board has quadrupled. For example, the 100% electric Renault Megane E-TECH presents new connected functions and new driving aids. This connectivity not only increases the amount of waves exchanged inside the car, but also with the outside. It is therefore necessary to ensure that all these frequencies do not conflict with each other, of course so as not to alter the operation of the equipment, but above all so as not to disrupt the safety around the vehicle and to ensure safe and reliable cars for all Renault vehicles. customers.

On that day, the new flagship of the Renault range and its equipment will be subjected to multiple tests, with a demand twice as high as the regulations require. Every reaction, every behavior is studied from the control room. Everything is examined and analyzed thanks to powerful computers. There should be no guaranteeing the effectiveness and reliability of connected car systems.

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

The various anechoic chambers and analysis labs scattered throughout the labyrinthine Aubevoye Technical Center accommodate a cumulative total of more than a thousand testing sessions per year. Long months before they are unveiled, and even before they have a name, future Renault vehicles spend whole days in these deaf and blind rooms, surrounded by invisible frequencies. Nothing is seen in anechoic chambers, nothing is heard, but the stakes are high in these little-known treasures of wave technology.

In the afternoon, when the light around Aubevoye goes out, Stéphane leaves his peculiar office. On your journey home through the Normandy woods, roll down the window and let the sounds of nature drift aboard.

Source: La Verdad


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