That is some fantastic explainin'! Thanks.

OK then with that effect in mind what materaisl and how they are constructed will create the least amount of hum?

klaa2 - THANKS for the lesson on induction! I think that's the best we had on this Forum. I know a lot of peopole had mentioned that the hum depended upon the type of pot or pan, but I knew that's wasn't all there was to it. My Viking makes the sound as soon as it is turned on. It's really not that bad though.

Sorry about the hijack, but had to post this thank you.

gng

Good explanation at high level but I am not sure I agree with all of it:

"Whenever you send a strong alternating electric current through a coil, creating a magnetic field, it will hum."

This is not always true. magnetostriction generates noise at twice the frequency fed to the transformer. If the frequency is high enough, then you don't hear it. Take your laptop power supply and listen to it. Do you hear a hum? No. That's because it is running at too high a frequency for your ear to hear anything.

From the bit of data I have seen on the design of these hobs, the interverters in these cooking units runs at 20-50 Khz. So the noise in theory should be inaudble. However, it appears that some efficiency can be gained from not filtering the AC mains in the process of converting to DC. This allows the input frequency to bleed through to the output, causing some amount of 120 Hz noise to exist.

OK, back to English :), I imagine a noise-free system can be designed but it would be less efficient and cost more. Since everyone shops for watts/BTUs here, I suspect such a unit won't see the light of day if my understanding of above is correct.

Klaa2, the sound you hear may be a cooling fan, not the hum talked about here. If so, someone was too cheap to make that load/temp sensitive and not have it come on with no load.

Oops. Meant to name Gneegirl instead of Klaa2 regarding fan noise :).

Armin - just because you can't hear it doen't mean it's not humming. It's simply creating hum at frequency inaudible to most human ears, perhaps other animals can hear it? So klaa2's explaniation would be correct you confirm as much.

You seem only to be re-hashing the debate of .....if a tree fell in a forrest, but no one is around- did it make a sound?

Thank you all for your kind words. My post was made to try to explain the reason why induction cooktops hum without complicated science. Armin is correct about the audible hum occurring only at certain frequencies but again, without getting too complicated, it suffices to say induction cooktops work at those frequencies.

The bottom line is that this is what causes the hum in these appliances.

Canuck99, or should I call you Gretz ;-), that's a good question. I could try to get into that, but I'm not that qualified. It gets a bit complicated because I believe certain materials, though they may better at silencing the hum, may also provide unacceptable performance and/or waste of energy. I'm sure the big appliance companies have Electrical Engineers designing this stuff.

Europe's electricity is based on a 50 Hz cycle, whereas ours is 60 Hz. Are there any Europeans here? Do you ever get a hum from your induction cooktop?

Does anyone here in the states with an induction cooktop have a line conditioner for their household electric? Do you get a hum?

Re: Whenever you send a strong alternating electric current through a coil, creating a magnetic field, it will hum."

This is not always true. magnetostriction generates noise at twice the frequency fed to the transformer. If the frequency is high enough, then you don't hear it. Take your laptop power supply and listen to it. Do you hear a hum? No. That's because it is running at too high a frequency for your ear to hear anything.

From the bit of data I have seen on the design of these hobs, the interverters in these cooking units runs at 20-50 Khz. So the noise in theory should be inaudible.

I believe that since the hum comes from the alternating magnetic field, the field that alternates 200-400 times per second, and not any transformer in the circuit. If I am right, the hum should occur around 400-800 Hz.

The link below provides an overview of induction heating. The process can be induced by several methods, but hysteresis effects are used for magnetic cooking pans, to maximize power transfer efficiency, I suspect. (I haven't had time to read the article in depth.) One can induction heat copper pans, but the copper coils doing the heating would get just as hot.

kas

Here is a link that might be useful: American Society for Metals: Theory of Heating by Induction

Below is an explanation i received from the Electrolux Director of Technical Services.

(In all induction cookers the majority of the "audible noise" during heating is directly related to the construction of the cookware and the power level applied.

Some factors that influence whether or not a piece of cookware is noisy or not ...

1) Encapsulated slugs in the base of the cookware. Most induction cookware manufactures encapsulate a ferromagnetic slug in the base of cookware. The benefits are they "will" work with induction, the heat is more evenly distributed within the cookware since these metals are higher density and distribute the heat evenly, and the cookware cost less to manufacture. In most cases the slug is "just encapsulated" and is not fixed (welded) inside the bottom of the pan. Because the slug can move within the encapsulation, the high frequency magnetic field will setup a mechanical vibration (audible noise).

2) Loose fitting handles on cookware is another cause of audible noise.

3) Pans with a non-uniform bottom that can vibrate on the glass surface causing audible noise, especially under higher power settings.

The cookware with the lowest noise levels are constructed of solid cast iron and are enamel coated. There are several brands that represent this construction - Silit and Le Creuset although they more expensive. Peggy can probably recommend others.

There are some low level noises such as a "tick" or "humming" can sometimes be detected. These noises are associated with power level control (rapid ON & OFF) and are present in ALL induction cooking electronics).

" I can confirm that the pan used makes a big difference to the noise level probably more than the brand purchased.

thanks armim for your comment on the "fan". That could be it. I actually don't hear much else once the pot/pan is on the hob. So I'm not too sure that issue makes a difference for the Viking. I have some junky cookware and some mid-range and then the emerilware - it doesn't matter. Not sure I could handle much more noice. It really doesn't bother me that much until when using the oven (also VIK) that darn fan runs for about 20 minutes. When using the oven and cooktop together, it will drive you nuts! But it's better than others here.

kaseki - thanks for your info as well. The Emerilware I have includes a copper disk. The instructions say don't leave the empty pot/pan on the hob with it on as it could melt the copper disk.

This is turning into a real science/physics lesson here. Pretty interesting stuff.

Thanks all...

I'm in on this. My Viking 30" all induction hums, yes. What really drives me up the wall is the intermittent "surging" hums that occur when the unit is idle. It is a ghost sound that will hum for about 2 seconds even after the unit is idle for hours and hours. Iassumed this is some kind of capacitor release.
I contacted Viking. They told me nothing.

Another bizarre thing is when I put a large paint blanket over the induction to protect it from paint spills. When I remove the blanket the whole unit is warm to the touch. Strange indeed.

Any ideas are appreciated.

What do you have around the unit? Any metal objects? It sounds to me like the unit is turning the induction coil on, just to turn it back off. That should only happen if there is something magnetic near it.

If the above is true, it would also explain the second thing. That is, the unit is running and it loses its natural cooling through surface when covered.

Of course, these are all wild guesses :).

My guess is that the cooktop has sensors to detect touch control, and these must be always on in order for the touch control to work, much as a television with remote control turn-on has a parasitic power drain waiting to detect the remote. Power drain implies heat output in the electronics, even when not cooking.

kas

That would not explain the hum though. That sound comes from either a fan or the induction coil being activated. I don't see, outside of a machine being broken, that either would occur in the process of detecting user input. The capacitive sensors and the microprocessor watching for them use little to no power. Certainly far less than what it would take to heat up a cloth covering the unit.