A strange, soft whistle travels along the street. It sounds like a noise made by a flying saucer, or something out of Star Trek.
In fact, it's an electric car. They sound very different from conventional vehicles — and that's completely intentional.
"For years, manufacturers have tried to make their vehicles quieter," says Stefan Sentpali, professor of Acoustics, Dynamics and Automotive Engineering at the Munich University of Applied Sciences.
"Now they have to deliberately add a sound to them," he says.
Without added noise, electric cars are so quiet that they can pass unnoticed by unwary pedestrians, the visually impaired or other road users. So by law, new hybrid and electric vehicles have to have added noise, known as an acoustic vehicle alerting system (AVAS).
No creaks or rumbles
"How exactly the cars sound is up to the manufacturers," says Sentpali. "It can be either exciting or plain - the important thing is that it sounds like a car."
Sounds have helped people to classify objects for thousands of years. "People have a certain expectation of what an object sounds like," says Sentpali, and this of course also applies to electric cars.
"The sound must be of high quality, it mustn't creak or rumble, because we subconsciously associate that sort of noise with something being wrong," he explains.
But how should they sound? Sentpali believes this is where science fiction can help. "People know how vehicles sound in sci-fi films, and they will use this as a guide for e-vehicles," he says. "They sound up to two octaves higher, like a soft, pleasant whistle."
Indra Koegler is a sound designer at Volkswagen. Together with Klaus Zyciora, head of design for the VW Group, and the musician Leslie Mandoki, VW has developed a futuristic sound for its electric series.
"E-mobility feels and drives differently, so it can sound different," says Zyciora. The trick is to create a sound for different groups that is perceived by all of them as pleasant and not disturbing.
A new world inside
Future VW e-vehicles will sound different, depending on their size. "Today, a conventional small car makes a different noise to a large sedan," says Koegler. The e-cars also sound different from the inside, for example in warning sounds and voice control responses.
"The most beautiful sound in a car is absolute silence," says Mercedes sound designer Thomas Kueppers. The German manufacturer is aiming for an almost noiseless driving experience.
In future models, such as EQS and EQE, however, there will also be added driving sounds that change when accelerating.
The range of different sounds includes starting, ready to drive, engaging the gears and so on. These driving noises are not ready-made MP3 or wave files, but the individual sounds of a real-time calculation. "Depending on the driving status, the sound changes. Behind this is a great deal of computing power," says Kueppers.
Renzo Vitale is responsible for the BMW Group's electric car sound. In the case of the Mini Electric, this includes the prescribed driving noise as well as the sounds in the interior. "When stationary, the electric car should sound friendly, light and bright; when driving, sporty and dynamic," says Vitale.
Together with Hollywood film composer Hans Zimmer, he is developing various interior soundscapes that are intended to provide an even more aesthetic driving experience. – dpa