Electric car owners sometimes miss the engine sound. That is why manufacturers have it made, sometimes even by a film composer. How should an e-car sound?
The sound tells you how deeply you press an accelerator: the higher the speed, the higher the pitch and the faster you accelerate. Unless you’re in an electric car, you hear almost nothing. Some find that a blessing, others miss the ‘vroem sound’ of pounding pistons.
For them, there are attachments for sale that turn a quiet Tesla into a dangerously roaring Lamborghini, a Chevrolet Corvette, or whatever you want. For example, the company Milltek Active Sound sells a kind of metal sound box with a speaker and electronics that you can have installed at the rear of the car. The system can then be controlled with an app that offers dozens of sound options.
It’s a bit like a digital camera that ‘clicks’ when you take a picture: it makes no sense, but the sound bridges the gap to the past and some users like that.
The Delft noise researcher Elif Ozcan Vieira understands such car drivers. Not only the sound itself, but also the association it evokes, guides our appreciation. Few people find the mechanical gurgling of an espresso machine irritating, because it is reminiscent of a nice cup of coffee and cosiness. A much softer sounding dental drill, on the other hand, makes many hairs stand on end. “I call it the Harley Davidson effect,” says Ozcan Vieira. ‘Fans associate the loud engine noise of that motorcycle with freedom, or the taming of a wild animal. They like that, so the manufacturer has never muted the sound too much on purpose.’
‘The experience of the BMW’
The manufacturers of electric cars have also been thinking about this for a while. Mazda, Renault, Porsche and BMW, among others, have been equipping their plug-in hybrid/electric cars for a few years now with ‘engine sound’ designed to match the image of luxury cars.
BMW has given a lot of publicity to this with the latest model, the fully electric i4 M50 the sound to be composed by the film composer Hans Zimmer, who created more than a hundred soundtracks, including those of The Lion King, Inception and The Dark Knight. The sound, which the driver can switch on and off, is emphatically not designed to sound like an internal combustion engine, says spokesperson Andrew Mason of BMW Group Netherlands. ‘It should match the BMW experience with a combustion engine, not simulate it. When you accelerate, the sound supports the push in the back, the feeling that you are going faster.’
That is right. Select ‘IconicSounds’ on the i4’s touchscreen and the car fills with a pleasant, deep hum with a second note that gets higher the faster you accelerate. This feedback feels familiar, especially in the ‘Comfort mode’. However, if you opt for the ‘Sportive’ option on the slip road of the highway, you will rather feel like you’re in a Boeing 747 taking off than in a BMW. Perhaps that is what some BMW drivers like to experience.
“You get a stronger experience when all the senses tell the same thing,” says sound designer Emar Vegt. As a graduating industrial design student, he joined BMW in 2009 because he realized that the sound design of the electric car deserves just as much attention as its visible appearance. He came at just the right time.
Until then, car manufacturer sound designers had focused primarily on dampening unwanted mechanical noises. A new era dawned with the arrival of the quieter, electric option. “My boss believed in it,” says Vegt. ‘He said, ‘We can’t distinguish ourselves with silence, but with sound we can.’
Balance between modern and familiar
Vegt stayed with BMW for seven years and is partly responsible for the sound of the BMW i3 and the i8. The BMW, he explains, should sound modern, futuristic and powerful. A fake combustion engine sound is therefore out of the question. At the same time, the sound should not be cold and alienating. ‘People like sounds that have a certain naturalness and credibility. In practice, such sounds often have a frequency range that is close to a human voice. Our ears are well attuned to that. Achieving that balance between modern and familiar is the challenge.’
Apart from an emotional experience, according to Vegt, the feedback also offers extra safety: whoever hears that the car is accelerating, is more aware of this and is less likely to accidentally drive too fast. Whether this actually applies in practice has not yet been thoroughly investigated.
The fact that all electric cars emit noise from the outside when they drive at walking pace is in any case due to safety considerations. Since 2019 writes a European law for electric cars to also be audible to cyclists and pedestrians when they drive up to 20 kilometers per hour. At that speed, electric cars make so little noise that road users with a hearing impairment would otherwise not notice them.
Ozcan Vieira does have a comment about this. Although it is of course important that cyclists and pedestrians do not end up under the wheels of all too quiet electric cars, the effect of this measure has been little studied. ‘We often act mainly out of fear in these kinds of cases,’ she says. ‘To my knowledge, not many representative simulations have been done, although that is actually necessary to know for sure which sound is desirable and which is not. Noise pollution is a major cause of stress in Europe. In that context, I always recommend not just adding ‘sound for the sound’.’