Designing Sound Effects To Gently Warn Pedestrians Of Silent Vehicles

Sound stylings for electric cars
Above: Acoustic engineers tested alert sounds for EVs against more common street sounds like a “big truck” or a common automobile (“Mitsu 1156 rpm”), to learn which were most effective and audible without being irritating. Credit: Quartz/Delta

We rely heavily upon our hearing to stay safe from moving vehicles. Combustion-powered vehicles make plenty of noise, of course. But electric vehicles (EVs) are so quiet at slow speeds that pedestrians and bicyclists can’t hear them coming. As a solution, manufacturers are adding artificial sound options to EVs, but how can they be sure those sounds will be the best choices for alerting passers-by?

Enter acoustic science. Quartz reports today that Danish tech firm Delta has created an assortment of potential EV sounds, and collected data on which are most effective at being audible to those who need to hear them (perceptibility), without creating noise pollution for everyone else (irritation). That metric was termed “suitability.” It’s not simply a question of louder volume, or decibel level: sometimes subtle qualities like sound frequency are what make a noise distinct to our ears.

In the U.S., EV warning sounds are not yet required by law. The European Union is in the process of approving legislation that will require EVs to have “pedestrian alert systems” by 2019.

This Renault Zoe EV allows UK drivers to select from one of three chordlike trilling noises, which are activated at speeds of 1-18 mph:

These soothing sci-fi hums gratify my inner nerd. (“Wide shot: In the distance, a sleek red craft floating three feet above the sand speeds across the tawny desert landscape…”) Delta’s acoustic research may help determine if they’re also effective at alerting passers-by to watch out for my EV.