How do electric cars protect pedestrians? Listen to it

INNOVATION

You’re walking through a car park and behind you an electric car sets off. It’s so quiet that you aren’t aware of it. And that can be a stumbling block. That’s why ŠKODA’s hybrid models are equipped with warning sounds.

4. 6. 2020

Electric cars and plug-in hybrids are very quiet when moving at low speeds. That helps reduce noise in the area, but on the other hand it can pose a risk to pedestrians who might not hear the vehicle. That’s why these cars emit a warning sound.

The first ŠKODA cars to get the new sound system, known as E-noise, are the plug-in hybrid ŠKODA SUPERB iV and ŠKODA OCTAVIA iV. As you can hear in the example, the sound resembles a combustion engine, with low frequencies that become higher as the car speeds up. And the sound abates as the car reduces speed, so pedestrians can estimate whether the car is speeding up or slowing down.

Striking a balance

The first job was to devise a way to install an audio device, which is basically a smallish full-range speaker in a waterproof case, in the vehicle’s engine bay. “The legislation requires the sound to be projected forwards towards pedestrians, so there aren’t many positioning options,” Orendáš explains. “Pedestrians perceive only a fraction of the traffic situation visually and use their hearing to know what is around them,” he adds, explaining why the sound is specifically for pedestrians. In the end they found space by the right front wheel for the new speaker case with an internal volume of slightly over 1 litre.

The speaker case is located by the right front wheel.

The legislation places a number of demands on the system known as AVAS (Acoustic Vehicle Alarm System). “The legislation determines the system’s minimum volume, but our goal is to offer customers the quietest car possible. That’s a bit of a contradiction, so experts from Škoda vehicle acoustics were called in to fine-tune the sound,” Orendáš says.

Under EU rules, fully electric cars have to emit a warning sound at speeds up to 20 km/h, because these cars are extremely quiet roughly up to that speed. “Then the car makes noise in the form of tyre contact with the road surface and aerodynamic noise, so the E-noise isn’t necessary,” the engineer explains. ŠKODA’s solution for its electric cars is that the noise gets louder up to a speed of 25 km/h and then gradually abates until the car reaches the speed around 30 km/h, when it is naturally replaced by other noise generated by the vehicle in motion.

Car sound recording in an audio studio.

The car also has to emit warning sounds when reversing at speeds of up to 6 km/h. Here, too, the plug-in hybrids’ warning noise imitates a combustion engine, but with different tones notifying pedestrians that the car is going backwards.

Futuristic-sounding hybrids

Creating a warning sound audio “signature” is something of an opportunity for carmakers, as well as an engineering challenge. Although the legislation prescribes which frequency bands the sound should use and at what volume (to an overall level of at least 56 decibels), designers can be a bit creative and adapt the sound to the given car’s character. “Plug-in hybrids get a sound that imitates a combustion engine so that everything matches,” Orendáš says, explaining the choice used in ŠKODA cars already heading out onto the roads.

The sporty OCTAVIA RS iV, for example, will have a sound character the same as standard OCTAVIA iV and SUPERB iV models. “Given the model’s specific design feature, however, the sporty character of the sound only comes into play during dynamic driving away from urban roads,” Orendáš points out.

ŠKODA OCTAVIA RS iV