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I installed a dimmer switch in my bedroom and got buzzing from the switch and from the incandescent light/fan on the ceiling that it was controlling. I took that same dimmer switch and installed it in my daughters room and got no buzzing from the switch or the light/fan. I tried installing a different dimmer switch back in my bedroom and it also buzzed, so it seems to be the location and not the switches that are the problem. Why am I getting this buzzing sound in my bedroom? With a regular on/off switch there is no buzzing, just with the dimmers. I removed the light bulb to see if that was an issue and it still buzzed. Thanks.

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    Same fan in each room? Is the dimmer approved for motors? (Most are not.) – isherwood Apr 8 '16 at 19:57
  • The light/fan combos in the two rooms are slightly different, but more or less the same. Both are operating incandescent lights. The fans in both rooms are not connected to the switch, they are both running hot. When I wired in the light/fan, I set it up so the switch only controls the light, not the fan. Because I wired them in this way, I figured I would be able to add dimmer switches to the lights at some point (now). – Dave McDonald Apr 8 '16 at 20:22
  • When you said, "different dimmer switch back in my bedroom and it also buzzed," was the light buzzing, was the dimmer buzzing, or both? – Ben Welborn Apr 8 '16 at 21:21
  • Both the light and the dimmer switch buzzed with both dimmers switches that I tried. – Dave McDonald Apr 8 '16 at 21:54
  • You are right, you should be able to add dimmers in that situation since you are not switching the fan, Maybe it's time to reboot into LED bulbs with smart dimmers, the bulbs are quite good now, payback period is quite short, and it'll even lower your A/C bill. – Harper - Reinstate Monica Apr 9 '16 at 3:38
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First let me just say, that I noticed that you did not ask, How do I stop a dimmer switch from humming?, but rather WHY is it buzzing (especially, here- not there).

Essentially, your dimmer is also creating or acting like a speaker, because it is physically causing air to vibrate, which is detected by your ear... in other words, sound is created by moving air back and forth. A speaker is made by inducing a magnetic field in an object (like a coil or a bulb filament) which exerts a physical force upon the (induced) object causing it to move and by default, move the air. The range of human hearing is 20 to 20,000 Hz and the frequency of the electricity in a residence is 60 Hz.

The reason it is happening in the dimmer is the same reason as the light bulb; some piece of the dimmer or a neighboring conductor is physically vibrating.

Why it is only in the one spot has to do with something called harmonics... and there is a long physics lecture involved. But in short, harmonic distortions happen because like-waves are additive, meaning that electric wave of similar frequecies (and amplitudes) will add together. The light bulb in the bedroom (or perhaps of the fan motor) and the dimmer are acting like tuning forks each causing amplification (or resonance of waves) in each other and the result is induced power which is strong enough to cause physical movements, and thus, audible feedback.

Of course, from the other discussion about how to stop it, the answer was to change the bulb (that's acting like a tuning fork- not mentioned).

  • Ben, thank you, that was a good explanation of WHY. I read the HOW thread already before I started this thread and none of it had helped. What really got me was why it was buzzing in one room and not the other. I did try removing the light bulb from the socket and still got the buzzing from the fixture and from the switch, so I concluded that the light bulb itself was not the issue. – Dave McDonald Apr 8 '16 at 21:59
  • Then the tuning fork in question is probably/possibly the fan motor... have you tried disconnecting the power from the motor? – Ben Welborn Apr 8 '16 at 22:02
  • Good call, I'll try that and let you know. – Dave McDonald Apr 8 '16 at 22:04
  • Do you think I would have to actually disconnect the wiring from the fan motor, or just have the fan turned off? – Dave McDonald Apr 8 '16 at 22:05
  • I turned off the fan but the buzzing continued. However, I was able to stop the buzzing by switching the light off at the pull chain (attached to the fan/light combo). That is with or without a light bulb in the socket. So, as you would say, the light fixture itself seems to be the other tuning fork. So it just happens to resonate at a similar frequency to the dimmer and the light fixture in my daughters room does not? – Dave McDonald Apr 8 '16 at 22:20

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