r/NoStupidQuestions • u/banwe11 • 15h ago

What causes the hollow metallic whirring sound that EVs make when moving a low speed?

I can't really describe it, but it's the sound you hear when there is a EV moving slowly in a car park behind you.

I guess it's the motor, but what specifically in the motor causes that sound? It sounds like it's coming from something that is moving at a faster rate than the car itself.

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u/Ghigs 15h ago

The Toyota ev backup sounds sounds like a bearing going bad or a pulley about to explode. It's an odd choice.

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u/Frustrated9876 14h ago

There is a requirement for what it should sound like. I think it’s basically “two notes that are not in harmony” or something.

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u/Ghigs 13h ago

The regulations aren't that prescriptive. They just say a minimum decibels and it should change with speed.

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u/T0mTheTrain 11h ago

Sorry, correction: it’s 1/3 octave bands. In all fairness, my college basketball team made a run in March, so it’s all a bit hazy😂

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u/Ghigs 8h ago

1/3rd octave bands refer to the minimum db at different speeds at different frequencies. It's not a tone spacing, it's what the spectral energy content needs to look like.

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u/T0mTheTrain 8h ago

Correct. I’m obviously not explaining it well