Volkswagen Magazine

THINK AHEAD

the sounds
of silence.

How should an engine sound that is actually silent? And how do you get this sound in the engine compartment? A visit to the experts in Wolfsburg who create the driving sounds for the e-Golf.

Text Christian Buck
Photos Kerim Delikan

Of course, a car is coming. Or not?

Somehow from the distance the sound clearly resembles an engine – and yet it sounds like something else too. That is the reaction of many people who hear the new e-Golf for the first time: they immediately recognise that a car is driving towards them. And they also notice that it can’t be any ordinary vehicle.

The creator of this dual impression is Gordan Matkovic and his colleagues from Vehicle Development. Three years ago they tackled something that at first glance may seem rather paradoxical: to produce a distinctive sound of silence. To be more precise, they began to create a virtually silent car sound for the new e-Golf. Under its bonnet, an electric engine generates the drive, and this is virtually silent. It really is a fine thing. But while this is good news for city-dwellers and environmental associations, for others it can be a problem. “Electric vehicles are so quiet that pedestrians often don’t hear them coming,” explains Matkovic. “This could be dangerous in traffic.”

Gordan Matkovic and his colleagues create the noises for the e-Golf. In a variety of tests, they determine how the silent engine should sound.

For the visually impaired in particular, the familiar engine sound is an important guide as they make their way through town. So, from early on, interest groups pointed out the problem with quiet electric vehicles. The United States has already reacted to this: from 2017, electric cars in the US must be acoustically detectable, and in the European Union a similar law is likely to be passed soon. Volkswagen also recognised the problem and took the initiative to begin working on sound effects for electric vehicles.

But what form should the sounds of silence take? This is where Gordan Matkovic and his colleagues get involved. Together with representatives from Development, Distribution and Volkswagen’s Board of Directors, they went in search of the perfect sound for the e-Golf. In the beginning, their freedom was virtually unlimited. Thanks to modern technology, they could have given the car practically any conceivable sound – that of a horse and carriage, a helicopter or a circular saw.

And so the initial discussions were quite lively. “Of course, tastes differ and that’s why there was a wide range of suggestions in the beginning,” remembers Matkovic. “Some people wanted the classic sound of a combustion engine, others were in favour of the sound of an approaching ICE train, and others wanted something completely new.” What was rapidly established was that the e-Golf shouldn’t announce its presence by anything resembling a ringtone melody or the beeping of a reversing lorry. The experts deemed these sounds to be simply too annoying.

» Electric vehicles are so quiet that pedestrians often don’t hear them coming. «

Gordan Matkovic, Volkswagen Acoustics

If possible, the sound system in the engine compartment should be subtly audible in the cockpit.

After various tests, they agreed on an acoustic compromise: the e-Golf should sound like a mix of combustion engine and electric machine. “The sound of a classic engine is pretty well known and also still fairly audible in a loud environment”, explains Matkovic. “And the electric part makes us stand out and makes people realise that this is a new technology”. But because it would take some getting used to, they decided against a purely electric sound: the human brain recognises the familiar engine sound immediately because we have internalised this since childhood as a warning signal in traffic. “That’s why there is no reason not to gradually increase the electric part of the vehicle sound in future, once we have become more accustomed to the new sound of electric mobility”. Once the basic decision was made, the acoustic experts went back to the studio and recorded both sounds. For the electric machine, they filtered out unpleasant whistling sounds and added deep frequencies – the result is a rich sound with an even frequency that resembles an ICE train setting off. The sound of the combustion engine was modelled on a four-cylinder, but the acoustic experts eliminated the sounds of the generator and the belt drive from this sound. “Of course, we could also have used a 16-cylinder”, says Matkovic. “But that wouldn’t have matched the car – the e-Golf isn’t supposed to sound like a Bugatti.“

Would you like to know how the e-Golf sounds? Just give it a try!

It is thanks to Volker Wehrmeyer and his colleagues from Electronics Development that it has a sound at all, because they developed the acoustic system that brings the synthetic sound to life. Their new control device resembles a miniaturised stereo system. In the small aluminium casing is an amplifier with 2x 20 watt output. In addition, it houses the memory for the sound file and a computer that is responsible for accurate playback. Later on, the control device will be installed in the radio shaft, behind the display. The developers are particularly proud of the loudspeaker, which works in the full engine compartment. “We had to generate a good sound with compact casing,” reports Wehrmeyer. “In addition, the loudspeaker has to be very robust – after all, it is exposed to moisture and high temperatures.” Together with the Belgian hi-fi specialist D+M, they designed a loudspeaker with a water-repellent membrane and a magnet that can even withstand temperatures of up to 120°C. The casing of heat-resistant plastic is also custom made. It makes perfect use of the small space behind the radiator grille on the right fog light and not only fits in the e-Golf, but also in other Volkswagen models.

How exactly the car sounds depends above all on its speed: when it’s standing still, it’s inaudible. After setting off, the volume of the e-sound first increases linearly and then remains constant between 10 and 30 kmh. At even higher speeds, it slowly decreases again and at less than 50 kmh the loudspeaker remains completely silent – because at 40 kmh the rolling noise of the tyres plays the main role when it comes to sound. In addition to the volume, the electronics also vary the speed of playback: the faster the e-Golf is driving, the higher the pitch. And ultimately the accelerator also plays a role: when the driver is driving at a pretty nippy pace, the car becomes particularly audible.

To optimise the driving noise of the e-Golf, the experts performed extensive tests with it in an acoustics hall.

Of course, the technology is capable of even more than this – for example, it would be no problem to download new sounds from the Internet and give the car a different sound to suit the occasion or mood. “But this is not an option for us”, says Wehrmeyer. “We don’t want to orchestrate anything with the sound: the e-Golf should always sound like an e-Golf and not like a Porsche”.

» The e-Golf should always sound like an e-Golf and not like a Porsche. «

Gordan Matkovic, Volkswagen Acoustics