Automakers facing e-car sound dilemma

Christoph Meier, a sound engineer at Mercedes-Benz, typically spends 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 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 company.

Daimler isn’t alone in adding noise to electric cars. Renault 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. With electric cars already struggling to gain popularity, a spate of accidents could further dampen demand.

“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.”

While no data exists on injuries caused by electric vehicles, the EU has proposed legislation making acoustic warning sounds mandatory, and worldwide guidelines are expected in early 2014, according to German auto association VDA.

Blind and visually impaired people, who rely on acoustic cues to navigate through city streets, could be most at risk.

Without noise, “we could step right in front of a vehicle and the driver would have no chance to brake in time”, said Gerhard Renzel, who is blind and a traffic expert for the German association for the visually impaired DBSV.

Electric vehicles are mainly silent at speeds less than 30km/h. 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 Centre of Automotive Management at the University of Applied Sciences in Bergisch Gladbach, Germany. “It’s a justified goal to have quieter cities.”

Because of this, some carmakers are seeking to keep the din of electric vehicles to a minimum. BMW will add artificial sound to the i3 city car only where authorities demand it. Volkswagen also is not planning to add sound to its e-Up! model unless required.

Daimler, by contrast, sees sound as a safety feature. On the electric Smart, the engine tone is standard in the US and Japan and an option in Europe. Unlike Renault, which equips its Zoe, Kangoo, and Twizy electric models with sound, the German company does not allow customers to shut off the noise manually.

Smart’s sound mimics the noise of a combustion engine by getting louder as the driver presses down on the pedal and higher as the car accelerates. Daimler will equip electric Mercedes models 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.”