Is a slight hum in my subwoofer normal?

Discussion in 'Archived Threads 2001-2004' started by Matt Harwood, Apr 8, 2002.

  1. Matt Harwood

    Matt Harwood Agent

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    Shutting down my system tonight, I noticed a slight hum coming through my new subwoofer. It isn't noticable when there's music or video playing, but when the room is quiet, there's a definite hum.
    Is this normal? Anything I can do to eliminate it? Right now, my A/V equipment is running on its own dedicated 120VAC circuit, and the sub is fed using a quality RCA cable from the LFE port on the receiver.
    Thanks for your help.
     
  2. ThomasL

    ThomasL Supporting Actor

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    Greetings again Matt [​IMG] I see once you have one problem solved, another pops up.
    My model sub do you have?
    My subwoofer also makes a humming sound or "gurgling" sound when everything is off and the house is completely quiet. I have a Paradigm PDR-8 and after reading reviews of it over at www.audioreview.com have found that this is a normal occurrence it seems. I would be interested in knowing any solutions you happen upon.
    cheers,
    --tom
     
  3. Harold_C

    Harold_C Stunt Coordinator

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    If you have any 60 Hz hum (either from a ground loop) or induced AC noise on the long RCA cable to the subwoofer, this will be right in the sweet spot for a powered subwoofer to make it audible.

    On thing you can do to minimize it is to turn the volume knob on the subwoofer as far down as you can and still balance the system. The more you turn up the knob, the more you will amplify any noise picked up by that long cable run.

    For example, say that you could calibrate the system properly with the subwoofer knob up halfway and the receiver's subwoofer calibration level at -10 dB. This would would be noisier than getting the same output by setting the subwoofer knob at 1/4 and the receiver's subwoofer level adjustment at 0 dB. (ALL hypothetical settings just used for this example).

    You want the hottest possible signal coming from the receiver to the sub and the least amount of gain in the subwoofer amplifier to reduce your noise.

    Any audio system connected to a cable TV or antenna lead is going to be particularly prone to ground loops. Your AC electrical system is grounded to a copper rod driven into the ground at the service entry point to your house. The cable company grounds their wire (usually to a different copper rod driven into the ground). Since everything in your audio system is grounded to these two different rods, you have the potential for a ground loop which will cause 60 Hz hum. If it's just something you hear with no signal in a very quiet house, count yourself as lucky!

    If it's a bad ground loop problem, it will make the system absolutely unlistenable and has to be solved through trial and error of breaking various grounds at various components -- either by cutting the sheild on RF cables, audio cables, or defeating a three-pin AC cord -- one at a time until you isolate and cure the problem.
     
  4. Matt Harwood

    Matt Harwood Agent

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    I have a JBL PB12 sub. The hum was only barely audible after I switched everything off. Seems like this could be normal.
    Thanks for the input.
     
  5. Cave Canem

    Cave Canem Auditioning

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    I just noticed this myself the other day. I have the Sony SA-WM40. I will have to readjust when I get home to see if I can get it to go away. I usually leave it on 'auto-on/off' so I dont have to mess with it but lately its been humming. I have recently 'tweaked' it a little so maybe I tweaked it a little to much. [​IMG]
     
  6. ace peterson

    ace peterson Second Unit

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    Matt-

    I have the same sub, PB12. Mine hums quietly all the time just like you say. You can't hear it when playing anything, but when all is powered off and the room is quiet you can hear it. According to JBL, the hum is normal for their subwoofers. I tried the tricks that others have mentioned here at the forum, but nothing takes it away.

    Ace
     
  7. Matt Harwood

    Matt Harwood Agent

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    Thanks for the replies. The hum isn't distracting when listening, but with all the other hassles I've had, I was afraid this was another one. I'm glad it's not.
    By the way, the JBL rocks.
     
  8. steve nn

    steve nn Cinematographer

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    I'm sorry to here about humm but I am some-what relieved to for I have the same.I can turn my gain up to 1/2 on back of sub and then the hum starts.It has not been a problem though.With it set to 2 1/2 to 4 on the sub and the receiver set to -5 to +5 it works fine.Just depends on what I'm watching,my mood and who is home.I have the Vel ct.150.It will do the same with my spare sub to.
     
  9. Greg_R

    Greg_R Screenwriter

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    Unplug your CATV or DSS connection to your HT. If the hum goes away, you have a ground loop issue. Other sources of hum in a powered subwoofer are the transformer (not tightened down enough or damaged) and servo control mechanism (_very_ faint hum).
     

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