Sound & Signal
Quiet cars and the noise engineers had to add back
Electric vehicles were too quiet to be safe at low speed, so regulators required them to make a sound. Somebody had to decide what it should be.
The theory of vehicle sound is well covered elsewhere. This is about the version you meet in practice.
What holds up in practice
- Pedestrians, particularly blind pedestrians, rely on engine noise at low speed.
- Several jurisdictions now mandate artificial sound below a speed threshold.
- Above that speed tyre and wind noise dominate anyway.
Engine noise was doing safety work nobody costed
Pedestrians locate approaching vehicles by ear as well as by eye, and blind and partially sighted people rely on it heavily. Internal combustion engines are noisiest at low speed and low gear, which is exactly the situation in car parks and side streets.
Electric drivetrains are nearly silent in those conditions, which removed an audible cue that road behaviour had been built around. A pollutant turned out to be carrying a safety function as a side effect.
Regulators required the sound back
Several jurisdictions now require acoustic vehicle alerting systems on electric and hybrid vehicles below a defined speed, typically in the region of low urban speeds. The requirements specify audibility and frequency characteristics rather than a particular sound, which leaves manufacturers considerable latitude. Details, thresholds and implementation dates differ between countries, so any specific figure should be checked against local rules.
What is easy to forget is that it is one of the few cases of a regulator mandating that a machine be made noisier.
Above a certain speed the argument disappears
Tyre and wind noise dominate vehicle sound above roughly urban speeds, so an electric car on a motorway is not markedly quieter than any other. That is why the requirements apply only at low speed, and it is frequently misunderstood in public discussion. The overall noise benefit of electrification is real and concentrated in slow urban traffic.
Precision about where the benefit occurs makes the case stronger rather than weaker.
Somebody had to design the sound
Manufacturers employed sound designers to create alerting tones that are audible, directional, non-irritating and identifiable as a vehicle. The results vary widely, from synthesised hums to deliberately futuristic tones, and several have been changed after complaints. Designing a sound that a whole society will hear thousands of times is an unusual brief with very few precedents.
Most such briefs in history were solved accidentally by a machine rather than deliberately by a person.
Interior sound is also manufactured
Many combustion cars already pipe engine sound into the cabin through the audio system or use resonators to enhance it. This was widespread before electrification and is generally not advertised, which caused some controversy when it became widely known. Electric vehicles do the same with entirely synthetic sounds intended to convey acceleration.
In hindsight, the sound of a car has been partly fictional for longer than most drivers realise.
Dates in this period are approximate; the change was gradual and nobody logged it.
The city may end up quieter and stranger
Widespread electrification could substantially reduce urban traffic noise, which has documented associations with sleep disturbance and stress. What replaces it is a set of designed tones chosen by manufacturers rather than an emergent mechanical noise. Whether a city of designed sounds is better to live in than a city of engines is not a question anyone has been able to test yet.
In truth, it is one of the few disappearances currently in progress that can still be shaped.
The takeaway
We removed a noise nobody wanted and discovered it had been keeping people alive, so now a committee decides what cars sound like.
What replaced it works. That is not the same as it being nothing.
Questions readers ask
Why do electric cars make an artificial noise?
They are close to silent at low speed, which removes an audible cue pedestrians rely on, particularly blind and partially sighted people. Several jurisdictions now require an alerting sound below a set speed.
Are electric cars quieter on the motorway?
Only marginally. Above urban speeds, tyre and wind noise dominate for all vehicles, which is why the noise benefit of electrification is concentrated in slow traffic.
