olsonexi

Why do many microwave ovens hum in an interval of a minor 7th?

https://lemmy.wtf/post/2437281

Why do many microwave ovens hum in an interval of a minor 7th? - Lemmy.wtf

Something that I’ve noticed across most of the microwave ovens that I’ve used is that when they hum while cooking food, I can pick out 2 distinct tones. One of them is pretty clearly 60 hz from the AC power frequency. The other is consistently a minor 7th above that (which would be somewhere around 106-108 hz depending on the exact ratio). What causes this 2nd frequency to be produced?

Nov 30, 2023 at 8:45amWeb
Show threadotterNov 30, 2023
I honestly have no idea, and never before knew that I do not.
Show threadxkforceNov 30, 2023
reddit.com/…/why_do_microwave_ovens_make_such_a_d…
Why do microwave ovens make such a distinctive humming sound?

When I look this up the only answers I come across either talk about the beep sound or just say the fans are powerful. But I can't find out why...

reddit
Show threadCameronDevNov 30, 2023

Could it be the motor?

The second harmonic from 60hz is 120, which is close to where your hearing it? For what its worth, i get a peak at 100hz, which for the australian grid would make sense?

Show threadolsonexiNov 30, 2023
I checked against a tone generator, and realized that the lower frequency was actually 120, not 60, so I’d guess you’re probably hearing the same thing. That puts the higher frequency at 212-216, which I also checked and that range matches what I’m hearing (for 100hz, it should be at around 177-180).
Show threadClay_pidginDec 1, 2023
Interesting. I saw mostly 38Hz, 117, and 240. 100W LG microwave on US 60Hz with an audible fan.
Show threadCameronDevDec 1, 2023
Mine is also LG, not sure what its power output is, but i think its either 1000W or 1200W, yours must take forever to heat anything 😉.
Show threadMr_BlottNov 30, 2023
Do people actually use microwaves for cooking or is that just a meme?
Show threadCameronDevNov 30, 2023
What do you use it for?!
Show threadMr_BlottNov 30, 2023

Collecting dust. Popcorn.

Literally nothing is cookable in a microwave without it being disgusting

Show threadSpaceNoodleNov 30, 2023

What do you think is happening to the popcorn when you put it in the microwave?

Anyway, microwave popcorn is disgusting.

Show threadMr_BlottNov 30, 2023
How do you recommend cooking popcorn, Mr Blumenthal?
Show threadSpaceNoodleNov 30, 2023
In a popcorn popper …
Show threadMr_BlottNov 30, 2023
Right tools for the job, eh
Show threadCameronDevNov 30, 2023

Disgusting how?

I mostly use mine for reheating stuff, but cook the occasional two minute noodles or frozen pie. Never had it be disgusting, at worst it can be cold if not done long enough. Cutting the food up and stiring it around halfway through helps.

Show threadaccideathNov 30, 2023

Yup, also primarily use it for reheating food. Sometimes, when I’m lazy and just want sth to eat, I’ll make myself microwave potatoes. And I also use it to defrost frozen vegetables or fruit sometimes.

However, when I was living in a one bedroom apartment, which didn’t have an oven in the kitchen-corner, I had a microwave with integrated oven and with that I was able to bake myself anything that fits into a pizza sized round baking tray. Still love that thing. It’s a 30 y/o hand me down Siemens from my uncle that still works perfectly. It’s also rather large (about twice the size of a normal microwave) and sadly doesn’t fit into my current kitchen…

Show threadElderWendigoNov 30, 2023
Maybe you’re just doing it wrong. It’s a poor craftsman that blames their tools. I don’t get mad at the toaster for being bad at boiling water.
Show threadMr_BlottNov 30, 2023

I’ve been trying to think of things that a microwave is better for, and could only think of melting butter. Though a small saucepan does that too.

A fan oven or a frying pan or a grill all cook stuff 10x better than a microwave

A craftsman wouldn’t use the worst tool for the job, after all

Show threadThereforeNov 30, 2023

Microwaves are fantastic cooking tools, and I’m pretty confident you’re not using yours to its potential. Defrosting, reheating, steaming, boiling. Does it all in half the time with half the mess. All those settings on the keypad do something good. Most people just wack a few numbers in and let the microwave literally cremate the food on full power. Those reheat and defrost settings apply microwave then switch to low or no power, leaving the applied heat to radiate internally before repeating. Different densities and starting temperatures are accounted for.

Obviously you wouldn’t cook a stir fry or a steak in a microwave. Potatoes before roasting though? Dumplings? Frozens? Yes please Mike.

Show threadHerrBeterNov 30, 2023
Mashed potatoes : Dice small, 10-15min Rice: 1,5dl water to 1dl rice, 10-12min I could go on. It’s a big water heater
Show threadSpaceNoodleNov 30, 2023
Why have I not been microwaving rice? Does this affect the texture at all?
Show threadHerrBeterNov 30, 2023
Only if you don’t turn down the power, you want full effect to get in to temp and then turn it down to keep temperature steady
Show threadSpaceNoodleNov 30, 2023
So, not what you said, then
Show threadHerrBeterDec 1, 2023

I don’t think I specified, but much like cooking rice on a stove top you won’t run it at the same temperature. The microwave will use less energy than a traditional stove top, not sure about induction ones. And after learning to boil things with it, I do it all the time.

Just get it to boiling then 450 then if needed 300

Show threadClay_pidginDec 1, 2023
I’ve never seen someone use Deciliters before! Love it.
Show threadilinamoratoNov 30, 2023
It does passable baked potatoes too, but if you microwave it for about half the time and then toss it in some oil, kosher salt, and pepper and put it in a hot oven, you get great baked potatoes in far less time than in the oven alone. You’re basically boiling the middle and baking the outside. Great combo.
Show threadPrimarily0617Nov 30, 2023
frozen peas
Show threadOhmsLawnNov 30, 2023
Reheating, generally.
Show threadKISSmyOSNov 30, 2023
30s-1min in a microwave will make old bread soft again
30s will melt cheese
other than that, I use it for reheating food and heating up spiced wine.
Show threadShalakushkaNov 30, 2023
I like how instead of imagining there might be something you don't know about microwaves, you just kind of assumed everyone bought a dust and popcorn machine for no reason. It's such an "am I so out of touch?" moment.
Show threadarinNov 30, 2023
Op uses it for music
Show threadAukNov 30, 2023
Yes, microwaves are a poor substitute for an oven but they work fine for vegetables that you might otherwise use a steamer to cook. Stuff like broccoli, beans, carrot pieces etc. Corn on the cob works well too, just give it a few minutes in the microwave with the husk still on.
Show threadilinamoratoNov 30, 2023
Anything that’s ok mushy, really. You can also use it to start cooking something.
Show threadClay_pidginDec 1, 2023
Great for reheating leftovers, if it has a good humidity sensor.
Show threaddpunkedNov 30, 2023
Do you also observe this when running the microwave on max power? Usually, when a microwave states its 800 watts but you can adjust it down, it actually only changes the duration that power is supplied. So 400 watts would be 50% of the time the power is supplied at max.
Show threadPilkinsNov 30, 2023
There is a fan running and then the actual microwave itself. If you lower the power setting, you can hear the fan stay on consistently but hear the microwave shut off and on. If the power is at 100%, the microwave runs the entire time.
Show threadlolcatnipNov 30, 2023
A few microwaves don’t do that because they’re able to continuously run the magnetron at less than full power by using an inverter instead of a transformer.
Show threaddirtypirateNov 30, 2023
you're hearing the magnatron's power supply
Show threadkaupas24Nov 30, 2023
50 / 60 hz from the transformer under load?
Show threadCADmonkeyNov 30, 2023

There are two things making noise in the microwave when it’s running. There’s the transformer that’s making the high voltage for the magnetron, which is you 120 Hz noise you’re hearing.

The other noisy thing in the box is the fan. The fan is most likely a three blade metal fan running on a little shaded pole induction motor. That motor is very simple, just one moving part, and two poles. Two poles at 60 Hz gives us 3,600 RPM, which the motor can’t quite reach because as the RPM gets closer to that magic number of 3,600 rpm, the motor draws lesa current and makes less power. This difference between the speed the motor is trying to run (“syncronous speed”) and the actual speed is called the “slip” and is probably around 3%-5%. This gives us a fan speed between 3400 and 3500 rpm.

I don’t know if that is giving you the second noise you’re hearing, or if it’s mixing with the transformer noise to make it. But now you’ve caused a situation where I’m going to be caught holding a guitar tuner to my microwave.

Show threadMangoNov 30, 2023
He did the math!
Show threadwheeldawgDec 1, 2023
Can I give a second upvote to just the last sentence?
Show threadCanadaPlusDec 8, 2023
Wow, I did not expect an actual answer to this one. It’s a good but very specific observation.
Show threadCADmonkeyDec 9, 2023
I don’t know much about music or why some sounds are more pleasant than others… but I do know about electric motors.
Show threadz00sDec 1, 2023

Why do microwaves hum

Because they don’t know the words, obviously