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pop over main caused by a fan?

Discussion in 'Sound, Music, and Intercom' started by Destrox, Feb 16, 2009.

  1. Destrox

    Destrox Member

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    I'm in the middle of an assembly in our theater. Since I'm bored in the booth, I started turning the small desk fan that we have next to the sound board on and off. I started to notice whenever I turn it on or off, there is a small pop over the main speakers. I listened to the individual mic and the main using headphones and the pop is not coming from the board. There's also no talkback mic left on (unplugged it to make sure). We're using a LS9 if that makes any difference. This has happened once or twice before. Anyone know what's causing this and how to fix it?
     
  2. Footer

    Footer Senior Team Senior Team Premium Member

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    Odds are your amps and the fan are on the same circuit. Motors can cause a lot of noise on a line. For that matter it could be anything audio related that is on the same circuit, such as EQ's, compressors, CD player, whatever. Stop messing with it and put it on another circuit. Also, a power conditioner will help clean up the power.
     
  3. Destrox

    Destrox Member

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    Once I realized it was the fan making the pop, I stopped. The amps are in the prop lofts back stage so would it make that much of interference to cause that?
     
  4. Stookeybrd

    Stookeybrd Active Member

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    Regarding your question: Yes, the fan can make that much interference. What Kyle is saying is that regardless of location, if the amps and fan are plugged into the same circuit than the noise will appear.

    You can test this (with the system off) by finding what circuit the amps are plugged into and flip that breaker and see if the fan turns on. If it won't turn on, they are on the same circuit, if not... it gets interesting.


    Good Luck!
    Cameron Stuckey
     
  5. Footer

    Footer Senior Team Senior Team Premium Member

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    It could be anything audio related plugged into the circuit. Does not have to be the amps. Cheaply made motors can cause all kinds of noise on the line.
     
  6. Les

    Les Well-Known Member

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    Is it plugged into an orange receptacle? If so, that receptacle is "clean power" designated for sound equipment only.
     
  7. museav

    museav CBMod CB Mods Departed Member

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    It may mean that for your facility but that is not true in general. An orange receptacle used to indicate that it was an isolated ground receptacle but even that has changed and now an IG receptacle will have an orange equilateral triangle on it. Even if it is an isolated ground receptacle, and many isolated ground systems are not properly maintained all the way back to the service entrance panel, that alone does not necessarily mean that it is "clean power" or derived power or dedicated for the sound system or on a particular phase or anything else.

    If the amps are at the stage and the fan is in the booth, I sort of doubt they are on the same circuit. They could be but they more likely might be on the same phase of the same panel. That's why I prefer to keep fans, pumps compressors (including fridges and water coolers), copiers, etc. off of the same phase and panel as the audio and video systems power.
     
  8. Les

    Les Well-Known Member

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    Actually, I don't have a "home" facility. But in any event, I try to avoid plugging non-sound equipment into orange receptacles :)
     
  9. TimmyP1955

    TimmyP1955 Active Member

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    Wire a .01/600V cap across the terminals of the switch in the fan. This may eliminate the pop.
     
  10. Destrox

    Destrox Member

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    It's plugged in just a normal power outlet. I don't think they are on the same breaker, but I'll try to figure it out. It's plugged into the same outlet as our electronic bell system (those speakers are automatically turned off when not in use) so it might mess those up a little if we turn off the power. And I'd rather not have to buy something to fix it since it's not too noticeable.
     
  11. photoatdv

    photoatdv Active Member

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    Just a thought, why not just leave the fan on or off during shows? I mean it is definately good to learn why this is happening and what curcuits everything is on, but if you don't want to buy anything to fix it then just don't turn it on or off during the show.

    I do second that sometime throwing breakers can be a bad idea-- especially if you don't know what is on them! We found that one out when we did trial and error to find the breaker for some annoying lights backstage that we couldn't get to go off (they were seriously screwing up out BOs). Unfortunately we found out in the middle of the show that the same breaker also had the stairwell light on it :(. We kinda got it for that one.
     
  12. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Beyond the noise travelling on copper to the same phase or circuit somewhere, there is always the ability to induce noise on an audio line, particularly if it's unbalanced and / or has a flaky shield. Ditto for equipment with less stellar shielding...

    So is the power cable for the fan running over any audio cables?
     
  13. Arclight

    Arclight Member

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    As others have indicated here; Sharing an inductive load such as a fan motor, with any sound system component can create problems. Even though your amps are backstage on another circuit, it's very likely the fan is sharing the same AC line as your mixer board. the preamps in your sound board are vulnerable to this sort of noise. It's not only noise 'on the line' that can be a problem, but having an inductive fan motor anywhere near a sound system component can create a problem because of stray 'RF'. Computer monitor screens placed near a sound board can also create a problem.
     
  14. jjkool

    jjkool Member

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    TimmyP1955 has it right with the idea of the cap for ON/OFF noise in particular.

    Arclight is the only person who sort of identified the problem; induction... although not in the right way.

    Most likely this noise is only heard when turning the fan OFF. One property of inductors is reverse voltage spikes. Ever notice when unplugging a heater that is on you see the power arc? Reverse voltage spikes are only caused in inductors when a circuit is broken, or in this case the fan is off. This voltage spike may only effect certain components of a system, which is why you may not hear it in the headphones. If I had to guess Id say its just happening in the output of the mixer (possibly only wires). These spikes can be as high as 1000v but only last for a few nano-seconds.

    Test it, put a 9v battery on an inductor (small coil) and touch the copper... you will feel nothing! Now remove the wire and you will feel the shock! <--- Dont try this is you have any medical conditions / equipment in you as it can damage pacemakers / defribs, etc.

    J
     
  15. airkarol

    airkarol Member

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    Look into purchasing something to clean up the power a bit. Furman and SurgeX make some great products. Also, like others have said, try to keep them on different circuits.
     

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