Prototypes of future Renault vehicles are subjected for hours to tests to develop the sounds that are introduced in the passenger compartment, those that emit the warning systems and those that are heard from the outside. All of this happens in the anechoic Aubevoye chambersin the Department of Eure where the Renault Megane E-Tech has also spent many hours, under the supervision of Stéphane, Head of the Renault Group Acoustics and Vibrations Service.
A anechoic chamber It is a room designed to fully absorb the reflections produced by acoustic or electromagnetic waves that reach any of the surfaces that make it up. It is isolated from the outside and from any source of noise or external sound influence. The Aubevoye Technical Center is a Renault engineering and testing complex located 100 kilometers northeast of Paris. It occupies more than 600 hectares and houses nearly 60 kilometers of runways, 44 test benches, 2 climatic tunnels and 18 corrosion enclosures. These facilities test the future vehicles of the Renault Group brands in any situation.
The insulation: the semi anechoic chamber
The first of the rooms has all its walls covered by foam panels from which horizontal and vertical prisms emerge that absorb sound and electromagnetic waves, reproducing the conditions of a free field, where there is no echo. “Since the floor is not covered, we speak more of a semi-anechoic chamber”, explains Stéphane. Inside of her silence takes on a new meaning. The slightest noise is perceived in a surprising way in the absence of any parasitic noise since the walls do not return any echo.
In the center and surrounded by a hundred high-quality microphones, the new 100% electric Megane E-Tech is located. The technicians 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.” Acoustic experts build and measure the complete sound architecture composed of sounds, both inside and outside.
Ten years ago, the Renault Zoe, the manufacturer’s first electric car, raised new questions about sound and “what to do with silence”. To solve them, Renault developed in these anechoic chambers a VSP (Vehicle Sound for Pedestrians) a sound that pedestrians hear when they are near a Zoe that is traveling at low speed. Today, the new Megane E-Tech presents various alert sounds for pedestrians.
Inside the passenger compartment, the disappearance of the engine noise gives way to other sounds such as that of the indicators, the jingling of the buttons or the loudness of the interfaces take center stage. “The driver and passenger in it are immersed in an acoustic and sensory experience that is part of the journey,” explains Stéphane.
Simulating driving: Faraday’s camera
Next to the first chamber is another room whose walls are covered in white panels that cover a thick layer of insulating materials. A second Megane E-Tech placed on a roller bench allows to simulate a driving situation. The car is bombarded by waves of different powers and frequencies through antennas that surround it.
A moving vehicle is surrounded by electromagnetic fields and you have to make sure that nothing alters the operation of the vehicle. In a Faraday camera the walls retain electromagnetic waves and isolate it 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, an expert in electromagnetic compatibility.
While sound waves have decreased in electric vehicles, electromagnetic waves have increased. The number of electronic equipment on board has quadrupled since the beginning of the century due to new connected functions and driving aids. The waves increase both indoors and outdoors.
At this facility, technicians make sure that all these frequencies do not conflict, and do not alter the operation of the equipment or disturb the safety around the vehicle. The Megane E-Tech and its equipment are subjected to multiple tests, with a level of demand twice as high as required by regulations. Everything is examined and analyzed thanks to powerful computers.
the anechoic chamber
The last room of the Aubevoye Technical Center, located behind a heavy door, is about 300 square meters and 11 meters high. The walls, floor and ceiling are covered with large foam cones. It’s the only one fully anechoic chamber of the Aubevoye Technical Center where experts test the wave reception of all vehicles, from Zoe to Master.
The different anechoic chambers and analysis laboratories scattered throughout the labyrinthine Aubevoye Technical Center they host a cumulative total of over 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.