On my walk to work the other day, something odd happened. While waiting for a light, I heard a strange wheezing noise coming from the street, like some odd bird cawing at me. I ignored it for a second, but eventually turned to see what it was: A back-up beeper, but not the traditional 1000 Hz tone we all know and love. It was a fancy modern one that used white noise — a white noise that no one on the road recognized.
A block later, while passing a laundromat, the same problem reared its head. An EV sitting at a red light, creeping up in anticipation of the green, silently worked its way into the crosswalk. This struck me as absurd, since EVs are mandated to make noise at low speeds, until I realized the car was emitting a tone — the same tone as the dryers on the corner. We can do better than this, and the best way to do it is with an old Casio keyboard. Let me explain.
We all know the beep-beep-beep of a large truck backing up, there’s a link between that sight and sound in our minds. With EVs, we’re still in an early enough stage of the technology that we can start building those associations. But, like the white noise back-up beeper, that noise has to be both distinct from its environment and instantly recognizable. Current regulations around tones and pitches do their best estimate at the former, but there’s really only one path to the latter: Consistency. The ideal low-speed EV sound isn’t just distinct from the neighboring laundromat, it’s also uniform between vehicles.
The reason your back-up beeper can change to white noise is because it isn’t actually regulated — OSHA mandates that the sound be present, but not what the sound is. NHTSA approaches this better with its requirements around pitch, but it could go further: A single sound, universal to all electric vehicles traveling at slow speeds. Through repeat exposure, that sounds — whatever it may be — will become ingrained in the public consciousness for its meaning, just like the 1000 Hz tone of a back-up beeper.
This, of course, brings us to the important question: What should that sound be? If one sound will emit from every EV, it’s something we’ll all be hearing a lot in the coming decades. Clearly, it can’t be something as annoying as a back-up beeper. Yet, it needs to be instantly recognizable as a warning regardless of any other din around. With the criteria of distinct, recognizable, and non-annoying, my vote would go towards something simple: A chord played on a synth.
Multiple tones reduce the likelihood of a similar sound drowning anything out, a synthetic instrument is unlikely to be mistaken for any naturally occurring audio, and a nice chord just sounds good to the ear. The worst possible outcome here is that crowded freeways suddenly become an angelic chorus of commuters jockeying for spots in slightly-faster-moving lanes. Or maybe that scene from La La Land happens. Regardless, it’s the best way to ensure our increasingly silent automotive fleet doesn’t hit pedestrians in crosswalks.