Why are electric appliances (e.g. blender, vacuum) so loud, when electric motors are quiet?
In: Physics
Because moving air is loud.
Sound is air vibration, and moving air with a ventilator happens to make air vibrate a lot.
For the blender it’s a sideeffect of the blade swirling in air (or food)
The motors themselves do not make much noise. The noise of a vacuum cleaner is from the fan and the turbulence created by the moving air. The noise from a blender comes from it crushing up things you put in it in addition to turbulence from the blades. Even a modern car with internal combustion engine usually have more noise come from its tires making contact with the ground then the engine itself.
I read that quiet vacuums have been made, but people thought they weren’t working well because the expectation was that louder = better.
There can be a bunch of different reasons.
First, there are different kinds of motors. “Brushed” motors are cheaper, but the way they’re put together makes them louder and more likely to break. “Brushless” motors are more expensive, quieter, and easier to maintain. But some high-quality appliances use brushless motors and are still loud. Why?
Size and cost are big reasons.
Appliance motors have to be very small and fit in small spaces. They generate a lot of heat and need to pull in air to cool themselves. There’s not a lot of room for sound dampening or vibration isolation, and it would make the appliances cost more. Further, a lot of the premium devices are sold based on how much power they have, and people think a louder motor has more power. (They’ve never thought about how a lawnmower is often louder than a car!) So not a lot of people are really shopping for a *quiet* blender or vacuum, especially if it means they become so large they aren’t easy to use or so expensive they aren’t worth it.
Car motors, on the other hand, are part of a very expensive purchase. People expect them to be quiet, it’s one of their selling points. The engineers have a lot of room, so ventilation is a lot easier to do and they have the budget to deal with vibration and sound dampening.
Electric motor makes an electric motor noise.
An electric drill makes: electric motor noise, motor cooling fan noise, gears noise, percussion noise, and the drill bit in the concrete at high speed noise.
Where is the mistery?????
In garage doors openers and ceiling fans, DC is preferred for quite operation. Having just replacing both garage door openers and most of my ceiling fans, I can confirm they are quieter.
Almost all small appliances use AC motors for cost savings. If they used DC motors they would be quieter in some conditions. If you are crunching ice, not blender is going to be quite.
People mention blenders for example being loud because of food getting crushed up, but they are loud without anything in it. I reckon this is a result of gears moving together
Partially it’s intentional. Cars and vacuums produce sound intentionally because it was found that not having the sound made consumers less likely to believe they were working as effectively.
The same applies to some websites and applications, even fast programs will have an artificial loading bar at some point because if they didnt then users would think nothing happened.
Humans have unintentionally been raised to expect noisy and laggy machines even when the technology exists to alleviate it.
Vacuum source: https://youtu.be/rZOpDve8ARA
Loading source: https://www.theatlantic.com/technology/archive/2017/02/why-some-apps-use-fake-progress-bars/517233/
Pretty sure vaccums are made loud for some “quality” reasons.
Like how some devices have weights in them to make them seem higher quality.
I do know the vacuums are loud because engineers tried to make quieter vacuums and the manufacturer started to get complaints saying the vacuums weren’t working. I don’t know if that is the reason for blenders or other appliances.
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