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Daimler invents 'fake vroom' to make electric cars safer

“People expect some exterior noise from a vehicle, because we all grew up with the ‘vroom vroom’ of combustion engines,”

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Christoph Meier, a sound engineer at Mercedes-Benz parent Daimler AG, typically spends his time making engine noise less jarring. For the carmaker’s new electric models, he’s had to do the opposite — create sound.

For Daimler’s e-Smart city car, Meier and his team invented a “sonorous purring” that was pitched higher than conventional vehicles, while Mercedes’s 416,500-euro ($569,600) SLS AMG Coupe Electric Drive gets huskier tones to reflect its power.

“People expect some exterior noise from a vehicle, because we all grew up with the ‘vroom vroom’ of combustion engines,” said Meier, who oversees 250 people as head of powertrain acoustics at the Stuttgart, Germany-based company.

Daimler isn’t alone in adding noise to electric cars. Renault SA offers a choice of car tones — pure, glam and sport — on the Zoe hatchback, while Nissan Motor Co.’s Leaf, the best-selling electric car, also comes with artificial sound. The issue has become more critical to carmakers as regulators look to require warning noises as soon as next year, while the rollout of more and more models forces manufacturers to seek ways to stand out.

Synthetic motor noise, like the jangly, high-pitched whir of Renault’s glam track, could save lives and at the same time protect investments in electric cars. The vehicles emit almost no sound at low speeds, making them a potential silent threat for cyclists and pedestrians used to reacting to the rumble of engines. With electric cars already struggling to gain popularity, a spate of accidents could further damp demand.

Not Looking

“If a silent electric vehicle knocks over an elderly person or a child, it’s not worth the risk,” said Neil King, an analyst with Euromonitor in London. “It happens often enough in urban areas that people are stepping into the road without looking. You can’t get around that.”

Although no data yet exists on injuries caused by electric vehicles, the European Union takes the threat seriously enough to propose legislation making acoustic warning sounds mandatory, and worldwide guidelines are expected in early 2014, according to German auto association VDA.

Electric vehicles are mainly silent at speeds less than 30 kilometres per hour. Then tire and wind noise kicks in. While adding motor sounds at slow speeds may help avoid accidents, it also undercuts one of the unique selling points of electric vehicles.

“One of the big competitive advantages of electric vehicles is their soundlessness,” said Stefan Bratzel, director of the Center of Automotive Management at the University of Applied Sciences in Bergisch Gladbach, Germany. “It’s a justified goal to have quieter cities.”

Smart’s sound, which is standard in the U.S. and an option in Europe, mimics the noise of a combustion engine by getting louder as the driver presses down on the pedal and higher as the car accelerates. The German automaker will equip electric Mercedes models — including a variant of the B-Class, which hits U.S. showrooms next year — with a similar system.

Still, the real dilemma is finding the right tone.

“Simply imitating the sound of a combustion engine was not an option,” said Ralf Kunkel, head of acoustics at Audi, who developed a tone for the A3 E-tron plug-in hybrid, which debuts next year. “We discarded ideas of giving electric vehicles sounds such as birds twittering or leaves rustling.”

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