Automakers are taking inspiration from rock bands and science fiction as they attempt to pick the right electric notes ahead of upcoming European Union regulations requiring battery-powered and hybrid cars to be fitted with an acoustic vehicle alert system to warn pedestrians of their presence.
Cars running on electric power instead of internal combustion engines are virtually noiseless at low speeds.
The EU, spurred by advocates for the blind and visually impaired, has put regulations in place to ensure that all new electric and hybrid vehicles launching after July 1 have an acoustic vehicle alert system, or AVAS, that is activated at speeds up to 20 kph (13 mph).
By July 1, 2021, all existing EVs and hybrids must be retrofitted. At speeds greater than 20 kph, tire and wind noise should be sufficient to warn pedestrians of a vehicle's approach.
Another regulation specifies the design of the alert system. Ideally, it should be similar to the sound emitted by an internal combustion vehicle of the same type. It cannot be a "beep" or other noise commonly associated with other warning sounds.
The sound has to be continuous and easily indicative of vehicle behavior, the regulation says.
The EU plans to revisit the noise regulations in 2021 to gauge their effectiveness.
In the United States, the National Highway Traffic Safety Administration has mandated a similar rule, which will take effect in 2020.
Volkswagen is giving its electric cars different sounds depending on their type.
Performance models will have a more assertive sound, with more bass, while SUVs will have a deeper sound to reflect their bigger size, VW's development chief, Frank Welsch told Reuters at the Geneva auto show this month.
VW's electric cars will have speakers designed to draw the attention of pedestrians, he said.
VW has already picked the sound for its I.D. battery-powered compact hatchback due to hit showrooms in 2020, but it is still tweaking tones for other cars based on the automaker's new MEB electric architecture.
The Renault Zoe small electric hatchback, which has been on the market since 2013, has a speaker near the motor that emits "an expressive range of sounds signaling that the vehicle is moving" -- with three settings: bold, neutral and sport, the automaker says.
Renault said its acoustic designers took inspiration from science fiction movies such as "Gattaca" and worked with a contemporary composer, Andrea Cera, to create the sounds.
Citroen says its Ami One concept, an electric urban runabout unveiled in Geneva, will have a sound "signature" that features "organic music blending male and female voices." The sequence of notes changes according to the vehicle's speed.
Citroen said the sound complies with the EU alert regulations.