Pedestrian warning noise in electric cars

After all, it helps us to perceive an approaching vehicle. The engines in our electric vehicles lack these typical sounds – and that’s exactly why a new regulation by the European Union (EU) asks every electric vehicle to make a warning sound so that they can be perceived in road traffic, even when driving slowly. But how must an electric vehicle sound to be identifiable for pedestrians and bikers? How do our sound engineers develop those sounds and what should you know about it? I had the chance to ask the experts from our Sound Quality & Sound Design team.

What is important to know about sound and electric cars?

Firstly, we need to differentiate a bit when it comes to the issue of sound. For one, there is the traditional noise emission, which always ensures a pleasantly quiet and comfortable background noise without any bothersome components. For another, electrically-powered vehicles are additionally equipped with a system that generates the external pedestrian warning sound (AVAS) required by law.

It is an unobtrusive but easy-to-hear sound, which gets louder from the start and is already faded out again from 20 to 30 km/h. We have created a pleasant and natural AVAS sound for the EQC (Stromverbrauch kombiniert: 21,3 - 20,2 kWh/100 km; CO2-Emissionen kombiniert: 0 g/km*). The system does not generate any science-fiction sounds that are strangely imposed on the car, but emphasizes the already existing noise of the vehicle and blends in seamlessly with the overall sound.

It is also important in this regard that the sound is not perceived as annoying in the interior. This is because the quiet electrics offer our customers added comfort and provide a noise reduction on our streets.

Is there a warning tone for the AVAS vehicle warning sound that all vehicle manufacturers must comply with?

The official rules define highly detailed parameters for what an AVAS may and may not sound like. This applies to the minimum and maximum volume as well as to certain sound components. Another provision is the speed range in which the sound must be audible.

Within this set framework, each vehicle manufacturer is free to design their own “electric sound.” The Mercedes-Benz AVAS sound differs only slightly for the EU, Japan and China. There are different requirements for the USA, e.g. in terms of the volume. In addition, a vehicle must already make a noise when it is stopped and a gear is engaged, and that noise must get louder up to a speed of 30 km/h. The deactivation of the AVAS by the customer is prohibited in nearly all countries.

How do you develop a sound of an electric car?

The background noise of the vehicle is first optimized in the simulation and subsequently on the acoustics test bench and on the test track. The primary goal is to develop the acoustic properties of the relevant vehicle components into a harmonized overall vehicle. This means that the perfect sound already starts with the body shell and the major assemblies and ultimately requires an optimization of a host of components that influence the overall vehicle noise.

In addition, AVAS literally requires “filling the gap” – complementing a sound where actually there is none – but one that perfectly blends in with the overall vehicle noise. On the one hand, the sound pattern should be discreet and not bother anyone in the long run, but should be easy to hear and intuitive to identify at the same time.

Apart from the large vehicle test benches, the engineers and sound designers also use the acoustics studio. This is where they analyse sounds in detail, evaluate them and perfect them jointly.

Is the customer able to select a personal sound for their electric car?

No. Each vehicle has its defined AVAS sound that complies with the particular legislation and cannot be modified or adapted to personal preferences.

In which models is AVAS being installed?

AVAS is installed as standard in all Mercedes-Benz electric vehicles and plug-in hybrids newly certified after July 1, 2019.

Do already registered electric vehicles / plug-in hybrids have to be retrofitted with AVAS?

No. The provisions apply to all newly certified vehicles. A sound generator was available as an option for our existing electric vehicles and plug-in hybrids. Retrofitting the sound generator is not a mandatory requirement.

What does an EQC sound like then?

The Mercedes-Benz acoustics engineers have achieved a special noise quality using a host of different measures. For example, the electric motors in the EQC are doubly isolated by rubber mounts: the electric motor from the subframe on the one hand and the subframe from the vehicle body on the other.

The elaborate isolation is complemented by noise insulation, and many detailed technical measures, to the components. The result: the EQC is extremely quiet in the interior. And from the outside – let’s put it this way: at slow speeds, the AVAS generates a clearly audible noise that accompanies the vehicle as it calmly and comfortably rolls along the street – without seeming artificial. And when reversing, a beeper sounds that is intuitive to recognize. Best have a listen yourself!

How do you become a sound designer for cars?

Sound designers and acoustics engineers often come from very different professional fields. Starting with electrical engineers and ranging to sound engineers, frequently with a passion for sound and music. An important skill is “analytical hearing” – that is to say, consciously perceiving noises and understanding why something is happening and sounds good – or why it doesn’t.

You can learn all of that – but ultimately what counts is whether the customer likes the sound design. The perfect sound is certainly also a subjective opinion. That is why the road to get there is frequently a complex and purposeful collaboration of the many people involved.