Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Popping noise from speakers when I turn the fan off

  1. Mar 25, 2015 #1


    User Avatar
    Gold Member

    I just noticed this and it is crazy. I have a little speaker that I plug into my computer. it is being charged by the usb port. I got up and turned off the fan in my room and I heard a popping noise. It worried me a bit, so I turned the fan back on (no noise), then I turned it off and I heard the popping noise again. It sounded like it came from the speaker, but I had to turn the fan on/off another 6 times to verify that everytime I turn off the fan, the speaker pops.

    Why would it do this? if it was due to electricity draw, wouldn't it affect my laptop first? wouldn't affect it when turning on the fan also? Maybe it is an electromagnetic field or something? This is strange.

    by the way, this is a ceiling fan. I was not aware they were on the same circuit, but it is entirely possible since this is a bedroom.

    edit: I unplugged the speaker and tested it again, and it does pop (though not as loudly) when it is not plugged into the computer. It has a rechargeable battery in it. So it must be magnetic. right?
  2. jcsd
  3. Mar 25, 2015 #2

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    It is possible that your house wiring makes a big loop on the way to the ceiling fan.
    That's a transmitting antenna for rapidly changing current.
    The fan motor being inductive does not allow a large rate-of-change of current when switch closes.
    But upon opening, there's arcing at the switch contacts and rapid change of current , much like when points open on an automobile ignition.

    I have opposite problem. Turning my computer ON makes my touch-dimmer lamps turn OFF. Computer is a capacitive load so rapid current change happens on switch closure instead.

    Move your switch real slowly and listen for noise. I had a defective switch causing awful interference with a nearby PA amplifier.
    My electrician was surprised when replacing the switch fixed the PA.
    Yours might be in process of contact failure from corrosion or weak contact pressure.

    old jim
  4. Mar 25, 2015 #3


    User Avatar
    Gold Member

    it's a brand new switch. I have been remodeling my house since hurricane Katrina and I just installed that switch a year ago. and, since this is a spare bedroom, I am just now beginning to use the switch because I have converted the room into an office. I don't think it is a failing switch. but your loop theory sounds like my theory with the magnetic field. If the fan is on the circuit with the outlets, then it would make a loop around the room. I'm not sure how it all works. my brother said a while back that the wiring is an old style of wiring. something like the hot goes straight to the fan or something. I don't know.

    as for the touch lamp. I have a touch lamp (not dimmer) that does the opposite. every time I lose power, when the power comes back on, the lamp does also. Are you saying that is because of the rapid current change running through the walls in a loop?

    edit: I did what you recommended, testing it real slow. and when I move the switch real slow, it does pop when turning the fan on. and it makes a real bad noise when turning the fan off. Like rather than popping, it makes radio static type noise when turning the fan off if I move the switch really slow.
  5. Mar 25, 2015 #4


    User Avatar

    Staff: Mentor

    The switch being new, it could be faulty since manufacture, then. Or perhaps the fan is lacking a suppresor condenser.
  6. Mar 25, 2015 #5
    The switch may be acting as a spark gap transmitter. As you open and close the switch an arc is jumping the contacts (and even more so when you do it slowly).

    Oh, I see Jim already covered this idea.
  7. Mar 25, 2015 #6


    User Avatar
    Gold Member

    it was just weird. :)
    didn't realize there was such a powerful magnetic field in the room changing so drastically due to the ceiling fan. :)
  8. Mar 25, 2015 #7


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    It takes very little radiated E/M power to cause things like that :)

  9. Mar 25, 2015 #8

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    Yes, if the hot and neutral are not run together then there's a loop. Pretty common in old houses where an electrician tied several neutral wires together, or connected the wrong white wires together in a junction box.

    Every circuit starts with a black and a white wire at the circuit breaker.
    The black wire is the one with the smoke in it, called "Hot". It's at 120 volts to earth.
    The white one is the return, called Neutral. It's zero volts to earth.
    All the current that goes out a black wire should come back through its own white wire, not through another circuit's white wire.

    If two white neutrals get swapped in a box someplace, current is happy to return through that neutral instead of its own.
    But it takes a different physical route, maybe along another wall making a loop around a whole room. Current in a loop makes an electromagnet....

    If several neutrals get tied together, current has several return paths to choose from so will likely divide among them.

    Here's a guy who explains such things well.

    http://www.mikeholt.com/technical.php?id=grounding/unformatted/emf&type=u&title=Electro Magnetic Fields (EMF)

    see also
    http://www.mikeholt.com/technical.php?id=powerquality/unformatted/EMIKarl&type=u&title=Power Quality Article
    Last edited: Mar 25, 2015
  10. Mar 25, 2015 #9


    User Avatar
    Gold Member

    Thankyou all. I better get back to studying relativity.
  11. Aug 5, 2015 #10
    a totally non-tech solution that worked for me was to turn the ceiling fan off with the pull chain instead of the wall switch. Never a pop, I just leave the fan on at the wall and use the chain...
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Popping noise from speakers when I turn the fan off
  1. Speakers popping (Replies: 11)