Imagine watching a small child ‘playing cars’. Whether pushing a toy car along the ground or mimicking turning the steering wheel, no matter where in the world the scene is set, the child will also be mimicking the sound of the car as it revs and speeds up.

But as we move towards a greater number of electric vehicles on the roads, that familiar ‘broom broom’ sound will be replaced by something completely different – a sound designed and engineered in a sound lab.

For Audi, developing the right sound for its growing fleet of all-electric cars is an important part of the development and production process, and with the e-tron GT about to commence production, developing the right sound, or suite of sounds for this exciting new model takers on even greater importance.

In Europe and the US, electric vehicles must produce a certain level of sound at low speeds to alert pedestrians and other road users as to their presence. Called the statutory acoustic vehicle alerting system (AVAS), in Europe it must be audible at speeds of up to 20km/h and in the US up to 32km/h. Audi has already spent considerable time and resources developing its own AVAS sounds.

But the sound developed for the e-ton GT by engineers Rudolf Halbmeir and Stephan Gsell in the Audi sound laboratory is so much more than just a warning sound. It embodies the soul of the brand’s first all-electric GT model and must stir the senses as much as the vehicle’s appearance and performance.

In the e-tron GT, for customers ordering the optional sound package, a second, large loudspeaker is added in the rear. In parallel, two loudspeakers in the interior provide a sound experience, with two control units continuously remixing the e-tron GT sound based on variables such as speed or accelerator position.

“In principle, the sound of a car has much in common with music,” says Rudolf Halbmeir. 

“To find the basis for the sound of the e-tron GT, I tried all sorts of instruments – from the violin to the electric guitar all the way to the didgeridoo. But none of them were really suitable. Then I came across a piece of plastic pipe lying in the garden, it was three meters long and had a cross-section of 80 millimetres. I attached a fan at one end and listened to the sound coming out the other end. It was a very specific, deep growl – and I knew straight away that I had discovered the foundation of the sound.” 

This was followed by traditional engineering work conducted both in the Audi sound laboratory and on the computer in the office. As a tool, he used a program that the team of Audi sound designers had written themselves, inspired by commercial software used for creating music. Halbmeir and his colleague Stephan Gsell used it to continuously develop the frequency structure into a finely balanced sample of 32 sounds. These include processed synthesiser sounds and, for instance, sounds made by a cordless screwdriver. The repertoire also features recordings of a model helicopter, and several variants of the plastic pipe can also be heard in the sound of the e-tron GT. 

“Our sound is continuously recreated as the algorithm mixes and prioritises the individual sounds differently,” explains Stephan Gsell. This is based on data about the rotational speed of the electric motors, the load, the vehicle speed, and other parameters supplied by the drive management. 

When the car is driven slowly, the e-sound is discreet, becoming fuller and more dynamic as speed increases. Although synthesised, it creates an authentic and finely nuanced impression of the work performed by the drive system. 

“We deliberately avoided imitating an internal combustion engine or a spaceship from a science fiction movie,” explains Halbmeir. “Instead, we developed a sporty, expansive and sophisticated sound that also comes across as clear and distinctive.”

Standard equipment includes the AVAS warning sound at low speeds emitted by a loudspeaker positioned in the front area of the car. With the optional sound package, customers can decide for themselves whether and how they wish to hear the e-sound. Two control units and amplifiers positioned in the boot area generate the exterior and interior sounds. In this configuration, the front exterior loudspeaker is joined by a one in the rear along with two loudspeakers in the rear doors for the interior sound. 

In the Audi drive select dynamic handling system, the driver can set how the e-sound is delivered. In efficiency mode, it is restricted to the AVAS warning sound. In comfort mode, the rear exterior loudspeaker comes into play and in dynamic mode, both exterior loudspeakers become louder, and the interior sound is added.