Acoustics, the brand new problem – AUTOMOBIL REVUE

The electrification of a vehicle fleet brings with it many new challenges to the industry. One of these challenges is acoustics, which manufacturers pay special attention to. Until now, it was the combustion engine and its auxiliary parts, such as the exhaust system, that attracted the attention of acoustics specialists. For good reason, because at a speed of less than 40 km / h, the noise from the combustion engine in the passenger compartment overshadows all other noises. In contrast, electric machines work with little noise. Therefore, specialists inevitably had to deal with this peculiarity. A paradigm shift for acoustics, whose attention is now turning to other drive components.

But what are the ingredients actually included? To answer this question, we visited the Renault Technical Center in Aubevoye (F). Established in 1982, it is a top-secret site where the new Renault range cars are tested with an entire area dedicated to sound. Tests are carried out not only on the test track, but also in anechoic chambers, that is, in test chambers whose walls absorb sound waves. There, Renault engineers explained to us that they are working to eliminate two major sources of noise. On the one hand, there is the rolling noise that the wheels make when the tires deform when rolling on the road. On the other hand, there is the wind noise that the car makes when the air penetrates while driving.

Acoustics have several solutions to reduce this noise. The first is the use of passive devices as soundproofing. In this context, it should be noted that the carpet placed inside the Megane E-Tech electric car no longer has to perform this function because it is now performed by the battery. It is so thick and compact that it does not allow very little noise to enter the interior. In other places, insulation panels can still be found, especially on the wheel arches and on the wall separating the engine compartment from the interior.

The problem of high frequency sound waves

The second solution that the engineers pursued consisted of active noise control and an active noise cancellation device. This is a noise reduction technology that uses additional sound sources. In the automotive sector, audio specialists use in-car speakers to generate sound waves that eliminate irritating noises. To date, this system can only be found in cars with internal combustion engines. “The problem with active noise cancellation is that it only works well at lower frequencies,” explains Frank Bellon, Renault’s acoustics specialist. Moreover: “It is much easier to reduce low-frequency waves from a combustion engine with active noise cancellation than high-frequency sound waves from other noise sources. There are physical reasons for this: due to their wavelength, low frequencies can be suppressed anywhere in the car. The more Frequency, you had to focus more on where you want to remove the sound, usually where the passengers’ ears are. In order to effectively suppress annoying noises, passengers have to stay in exactly the same position all the time, which is not the case.” However, this technology is already used in many headphones. So what’s the problem in the car? “Active noise canceling systems in headphones should only control the sound field in a few cubic centimeters of the auditory canal. This allows you to actively monitor a frequency range of up to 10,000 Hz. But if the volume to be monitored corresponds to the position of the head in the car, then the division should be The frequencies to be monitored are reduced to 10 or even 15 different bands”, responds Thomas Antoine, principal expert in acoustics and vibrations at Renault. Despite all the problems, acoustics engineers are still working intensively on solutions, and ANC systems can certainly be used in electric vehicles of the future.

Individually adjustable soundscape

In addition to the annoying noise that acousticians work to suppress, there are other sounds that they want to generate artificially. This is especially true for Vehicle Sound for Pedestrians (VSP), i.e. the noise made by vehicles to draw the attention of pedestrians to them. “This tone is required by law for all electric vehicles traveling at speeds less than 30 km/h,” says Thomas Antoine. Instead of seeing these regulations as a limitation, many car manufacturers are developing their own acoustic landscape for their cars: “Zoe customers can choose which VSP their cars emit. This is also possible with the new Megane E-Tech,” says Luis Ferdinand Pardo, acoustics specialist vehicles. Some manufacturers bypass legal requirements, for example by installing active audio systems up to a speed of 60 km / h.

“Aside from the noise the car makes to pedestrians, there is also demand for personal noise inside the car,” Pardo says. This starts with a sound that tells the driver that the ignition is on. Currently, most electric cars do not make noise when the engine is running. The lack of noise can be a problem for customers, as many turn the ignition off when they are about to go off. “Personally, this happens a lot to me, by the way,” Bardot admits. He is far from the only one. “In the future, we will offer the ability to customize the car’s audio system, for example by allowing the driver to adjust background noise when the ignition is turned on.”

That’s not all. “When switching from combustion to electric cars, a lot of acoustic feedback is lost. The lack of sound upon acceleration confuses many drivers. For this reason, many manufacturers are working to generate a synthetic sound based on acceleration and cadence,” Pardo explains. Within the Renault range, the next models that will benefit from the acoustic landscape improvements will be the futuristic Alpine E models, the electric SUV, the city car based on the Renault R5 and finally the coupe built in collaboration with Lotus. It seems logical that Alpine is the first to do so, as sound seems to be closely related to driving pleasure.

Acoustic tests are also performed outside of laboratories on test tracks.

original sounds

In the future, electric cars will likely have many acoustic properties: “In the future, vehicles will also be able to offer atypical acoustic experiences, for example a combination of music and synthetic sound.” Louis-Ferdinand Pardo is behind the wheel of Zoe, whose on-board computer has been sound-adjusted, and plays the “Star Wars” soundtrack. Above that, depending on the acceleration, the sound of a spacecraft accelerating to breakneck speeds can be heard, giving the driver the feeling of sitting in the Millennium Falcon. “Of course, it’s not about constantly having that kind of sound, it’s just about delivering atypical audio experiences to our customers that they can sometimes play through their infotainment system,” says Prado with a smile.

The topic of volume is one on which opinions differ: “Some like the sound, some don’t, and some only want the sound in certain situations.” For this reason, customization is very important. In order to generate sound, manufacturers will not be limited to data from the acceleration and speed sensors: “The soundtrack of the audio system can also use data from traffic light cameras, steering, brake and indicator sensors to create an individual sound signal.” In this way, the car becomes a chorus in which each device is A sensor is an instrument with which the driver, as a conductor, can compose a particular piece of music. In other words: for younger children, the car becomes a DJ set with which the driver can compose a techno piece himself. “These types of audio experiences can also be supplemented with a lighting effect,” Pardo adds. Matching created by interior screens and backlights.

It can also be a good thing too much

But it should not be overstated, says Thomas Antoine: “If the sound is poorly combined, an inappropriate or unclear sound in an already loaded sound profile will annoy the occupants.” The biggest challenge for the audiologist isn’t overstating it: “We gathered from customer reviews that there are generally too many audio signals inside the car.” Manufacturers are aware of the problem. This comes because the various development departments want to emphasize their role. “Most departments ask us to link the functionality they have developed to the audio signal. They don’t know, of course, that they are not alone in making this request. That’s why my job is to turn off certain audio signals. But you can’t turn everything off either, because there are certain requirements, such as legal regulations or Euro NCAP guidelines. The best example of this is the seat belt warning sound. If it’s not installed, explains Frank Bellon, the car gets one star less. So the whole job of an audio expert is to create a coherent world between what the driver sees and what he hears. “This is called the audio customer experience,” says Thomas Antoine. Admittedly a very exciting experience.

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