I mean in comparison with other motors, like power tools or even home appliances? Is it just sound insulation or is it a different kind of motor?
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Electric motors in power tools and appliances are pretty quiet as well, at least larger ones that don’t spin extremely fast.
Usually it’s whatever is attached to the motor that’s making a lot of noise. Power tools and mixers for example have a lot of (cheaply made) gears that are noisy, and for vacuum cleaners, hair dryers and fans, it’s the blades moving through the air that are responsible for most of the noise.
Electric cars usually have gears as well, but ones of a different design with tighter tolerances.
As far as the motors themselves are concerned, brushless motors tend to be somewhat quieter than brushed ones, but the difference is minor compared to the other stuff attached to the motor.
You’ve got two things working for the electric car. First off, the motor is so big that it doesn’t vibrate like a smaller motor. You still get noise but between the bulk dampening the vibrations and the scale meaning it vibrates at a lower frequency it’s harder to notice.
Second, the motors are buried in the frame of the car. The frame acts like a baffle, like you’re hiding your alarm clock under a pillow.
Many power tools, kitchen appliances and vacuum cleaners use universal motors, because they’re cheap and power dense, but they’re also very mechanically noisy. There’s also in many cases cheaply made gearing that’s noisy as well. Universal motors have brushes and are not very long-lived, so EVs use long-life brushless motors that are much quieter, and helical gears that cost more but are quiet and wear-resistant.
Road noise and insulation play a large part in noise reduction. Even the cheapest cars today have some kind of insulation.
Another is design. Cars only use straight cut gears for reverse, and usually only with a manual transmission. That’s why you hear that heat whine when a manual transmission car backs up. Some luxury sports cars use an angle cut reverse gear to avoid that noise. All the other gears are angle cut to avoid that gear whine.
Power tools and appliances are by design loud. Consumers equate noise with power. I heard a story about an insulated vacuum that was really quiet compared to others and consumers assumed it was weak because of the low noise and would return them. Some professional vacuums are well insulated and have a fraction of the traditional vacuum noise. Power tools use straight cut gears cause they’re cheap.
Another is RC cars. Even the hobby grade cars will use straight cut gears, though there are aftermarket alternatives for the ring and pinion gears for some 4wd models that are cut at an angle.
Another is noise from the electronic speed controls. You may hear a whine from the speed control on some tools and RC cars/boats/planes/etc…. It’s generally a low cost or light weight unit, and they could be built better insulated, but cost and/or weight is a factor.
Often enough, if you can remove and power the motor by just a battery, you will notice a huge difference in noise.
With a normal car, or a lawn mower or a gas powered weed wacker, the thing that is powering the device is literally explosions. It’s pretty noisy. The noise associated with an electric motor is just movement and tiny bits of friction because of moving parts.
But you are also right that a car is a big hunk of metal and ends up absorbing a lot of that noise
Mainly because, without any emissions controls, mufflers, bushing motor mounts, internal combustion engines are insanely loud. Unbearably loud, even with all of that technology a lot of engines are still noticeably loud at mid-RPM ranges.
In comparison, an electric motor has no induction noise, it has no exhaust noise, it has no combustion noise.
A cordless drill has double geared reduction so the motor can spin many times faster than the drill bit.
Most f the noise is from the gears.
Carmakers can make quite quiet gas motors, but market research shows people expect noise, so they add extra noise.
It turns out people don’t believe something is powerful unless it’s loud.
This is probably also true for power tools.
I wish they gave consumers a silent option.
https://www.thedrive.com/tech/22834/from-acura-to-vw-bmw-to-porsche-car-companies-are-getting-sneakier-about-engine-sound-enhancement
Bigger motors usually have lower Kv rating so they spin slower but with more power.
Slower = quieter usually.
On top of that, most robust electric vehicles don’t use direct drive motors. They’ll have gearing to manipulate the motor output so that the motor can run at its most efficient speed.
Combustion: explosions, noisy
Electric motors: no explosions, quieter but not noiseless.
If an electric vehicle seems completely silent it’s likely due to all the other noise around it from combustion vehicles.
Even with a “quiet” electric motor there will always be noise because of moving parts.
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