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Thread: Crazy subwofer woke me up.

  1. #1
    Flashaholic* flownosaj's Avatar
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    Default Crazy subwofer woke me up.

    I have this powered subwofer for my home stereo system. Three times now I've woken up in the early AM with the subwofer resonating and vibrating the entire house.

    When this happened, the stereo's power is turned off and the subwofer is receiving no signal, but it is plugged in. "Fixing" the problem this morning at 0420 involved unpluging the subwofer from the wall.

    The first time this happened a few months ago it freaked my wife out. The only two explinations I can think of are:
    1) There's a 20 foot co-ax cable connecting the stereo to the subwofer. The cable runs close to the power cords of the other AV components and I could be picking up some kind of interference, or the 20ft is acting like a radio antenna
    2) Electrical interference directly through the 120V plug.



    Other than isolating the subwofer and attaching it to a surge-protector and moving the co-ax cable farther away from the other components, is there anything I can do?

    Has this happened to anyone else on the forum?
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    Flashaholic* WildRice's Avatar
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    Default Re: Crazy subwofer woke me up.

    I too have had this problem, albiet not as loud. When the receiver was off a faint humm was emitted. just loud enough that it was annoying. I was running a grounded shielded cable. Since them I have put the sub under the receiver right next to the TV facing forward, and hooked up the sub power the the switched aux power on the receiver.

    Good luck

    Jeff


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  3. #3
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    Default Re: Crazy subwofer woke me up.

    Are the subwoofer and amp on the same electrical circuit? If not, then you may be picking up a ground loop (when two appliances are connected via interconnects/cables etc., but are running off two seperate grounds.) However, I am not sure a ground loop would be loud enough to wake you up. Ground loops typically have a 60hz hum.

    The best way to test this is to move the subwoofer over to the amp, and connect them so they share the same electrical circuit. If the hum is gone, well it could be a ground loop. DO NOT cut the third ground plug as some may recommend, it is not worth the electrical shock.

    I have had luck using the EBtech hum eliminators, but my scenario is little different with 100 foot speaker runs, and 1600 watt amplifiers (church sound system).

    http://www.zzounds.com/cat--2757

    I bought mine here.
    Last edited by creampuff; 10-17-2006 at 01:13 PM.

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    Flashaholic* chimo's Avatar
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    Default Re: Crazy subwofer woke me up.

    I get some stray hum from my powered sub as well. My sub has an auto on/off feature that will switch the unit on/off withthe presence of a signal on the input.

    I switched to a shorter, beefier cable and that helped a bit. You could also try plugging your sub into the same power bar as your amp/receiver to see if that helps.

  5. #5
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    Default Re: Crazy subwofer woke me up.

    speaker cables running parallel and close to electric wires will pick up the 60hz hum..if they have to cross each other make sure they are at 90degree angles, that is perpendicular to each other, for at least a foot or so before going in parallel direction again...
    wow, all you guys with powered subwoofers..all I have is a little 12" M+K amp- powered woofer, and I think it blows the roof off..you guys play the 1812 Overture alot?, or live howitzer recordings? or what? ;
    Last edited by TedTheLed; 10-17-2006 at 01:34 PM.

  6. #6
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    Default Re: Crazy subwofer woke me up.

    I'm thinking connection cables. Check the insulation and make sure there isnt any excessive pressure on them.

  7. #7
    Flashaholic* zespectre's Avatar
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    Default Re: Crazy subwofer woke me up.

    I have a similar issue, sort of, I live near the 50kw tower for the local jesus station and my speaker system used to constantly preach at me at a low level.

    Kinda "mmmph mmmmph MMMPH JESUS SAID mummmmph mumble mumble". Finally had to buy a couple of RF chokes and install them on the input cable.
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    * The Arctic Moderator * Sigman's Avatar
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    Default Re: Crazy subwofer woke me up.

    All very good suggestions - but the bottom line is that you have a ghost!
    -"Must control self"-
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    Flashaholic* Coop's Avatar
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    Default Re: Crazy subwofer woke me up.

    and for those wondering what a 60Hz groundloop sounds like:

    http://www.maycooper.com/60Hz.wav (+/- 1 second sample)

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  10. #10
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    Default Re: Crazy subwofer woke me up.

    Is this sub supposed to auto-detect signal to turn its power on/off? Or is it 'always on' and you are saying it suddenly started making sound? How old is it? A lot of conjectures can be made, but if it usually works OK, it's probably not your basic interconnection or cable positions. More likely IMO, a flaw in the sub's electronics. You could try shorting the input next time it does it and see if the sound goes away. Or just put the sub on a switched power outlet.

  11. #11
    Flashaholic* Trashman's Avatar
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    Default Re: Crazy subwofer woke me up.

    Crappy sheilding inside the subwoofer. I've experienced the same thing with my Bose Mediamate speakers before. I was actually picking up some local stations somewhat clearly. I didn't know what was going on at first, especially after I noticed I didn't have them plugged into any output source, but then I figured it out.

    Got any Ham or CB operators nearby? If they're running more power than they should be, and/or don't have their systems grounded properly, they can bleed over onto all kinds of stuff.

  12. #12
    Flashaholic* flownosaj's Avatar
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    Default Re: Crazy subwofer woke me up.

    Thanks for your replies everyone

    I don't believe that this is an auto-detect (on/off) with signal--this is a an older model JVC 5.1 system that I've had for something like 5 years. No noise whatsoever when the system not sending a signal, even when the subs on full power, so it may have something, I don't know for sure...


    As far as being on the same circuit--the living room electrical outlets are pretty much all on the same circuit in the breaker box. It's plugged into the outlet directly across the room from the AV stuff.

    I tried listening to the 60Hz loop but my laptop's speakers must not have that low of a range.

    I'm wondering if it could be picking up a stray signal as it works fine 99.9% of the time and only seems to go crazy around 04something.


    I guess I'll so the easy fix and just switch it off when not in use.


    Ted--I guess I could play the 1812 and see what happens
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    Default Re: Crazy subwofer woke me up.

    I pick up a bump, bump, bump, bump when the cops come through the area. I am guessing its picking up the radio or something as it comes and goes when I see them outside and its like when they key the mic.

  14. #14
    Flashaholic* Concept's Avatar
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    Default Re: Crazy subwofer woke me up.

    Strange goings on!

    I have a 12"sub in a custom box with an amp purchased separately and fitted. It has an auto signal detect feature and sits there happily with the mains on 24/7. All of the cabels are even pretty much thrown togehter, low voltage signal and 240v leads and never has this happened. I do get a little pop come out of the sub when the ceiling fan is swithched but this is normal as it is regulated by a capacitor and causes little spikes in the system, but they are barely audible. I have also known washing machines to cause electrical noise as they are switching a relatively large load in comparison.

    Best solution is a process of elimination. disconnect sig lead one night, rerun sig leads annother, plug into separate power circuit via extension lead.

    Is your neighbour doing late nioght welding???

    I hope you sort out your problem as everyone needs a good nights sleep.
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    Flashaholic* Lasernerd's Avatar
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    Default Re: Crazy subwofer woke me up.

    Is your cell phone anywhere near this equipment?
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    Flashaholic Rando's Avatar
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    Default Re: Crazy subwofer woke me up.

    I have a Polk Audio self-powered sub that "hummed" when I first bought my house. I checked the outlet with one of these and found that the ground wire had come loose. Reattaching it eliminated the problem. Worth a try, maybe your water heater or something is drawing a lot of current late at night and causing interference. Good luck.

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    *Flashaholic* James S's Avatar
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    Default Re: Crazy subwofer woke me up.

    I"m voting for bad cabling.

    If the shield is loose on the cable running to it, or if any part of the connection is loose you can end up with a signal path but no ground path which can cause it to make that horrific noise. It's like plugging in your powered computer speakers with them turned up all the way, while the signal is shorted to ground as you're plugging them in, they amplify all the noise on the ground!

    So check the cables going to it, is it crimped under the furnature somewhere? That can damage or short the ground to the signal. Does the plug on the back of your stereo look good and tight and clean? Clean it up and crimp the connector ever so slightly with your fingers to make sure the RCA jack is tight. Is it one contiguous cable? or did you hide an rca to rca connector under the tv to connect 2 shorter cables together which is now coming loose?

    Probably just the cable or connector somewhere cooling down and moving slightly to short it out, or disconnect the ground.
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  18. #18
    *Retired* The_LED_Museum's Avatar
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    Default Re: Crazy subwofer woke me up.

    If I had to guess without being able to see and meter the system, you probably have an intermittent ground somewhere between the sound source (line level I presume?) and the subwoofer. Disconnecting the ground connection at any line level or lower input will usually result in a nasty and very loud 60Hz hum at the speaker(s) - often with other noise thrown in there for good measure but not always.

    For standard line level inputs, this is usually (but not always) a coaxial cable terminated with male RCA plugs at both ends. The conductor inside carries the signal itself and the braid around that wire is the ground. If that ground braid were somehow broken or intermittent, you'll hear that nasty humming sound out of the speakers or subwoofer.

  19. #19
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    Default Re: Crazy subwofer woke me up.

    Ledm, could he fix that condition by running another wire from where ever the coax ground is attached to the speaker, (would that be the negative speaker terminal?) to a cold water pipe, or a good ground on an electric outlet, ie the screw that holds the face plate on the electric outlet is often a ground..?

  20. #20
    Flashaholic* Arkayne's Avatar
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    Default Re: Crazy subwofer woke me up.

    I've gone through my share of home theater subs from craigslist ventures and found some with bad rca connectors. If I wiggled and rotated the cable connector a certain way, I could get that constant loud buzzing going. I'd try swapping out your rca cable with a nice shielded type and take a close look at the female connector on the sub. If you can, unscrew amp on the sub and check out the connector from the inside. You might want to solder the leads to the connector if it uses spades.

  21. #21

    Default Re: Crazy subwofer woke me up.

    it's either a ground loop or your 20m of coax is acting as a capacitor....being inductively charged by nearby active coils (sounds a long shot but it does happen) i'd have my money on a ground loop...

  22. #22
    Flashaholic* flownosaj's Avatar
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    Default Re: Crazy subwofer woke me up.

    Thanks for your replies everyone.

    I wasn't able to replicate the noise when I tried messing around with it. I decided to replaced the cable last night with a better one and it was okay overnight.

    I'll give it a few weeks to see if this solved the problem.
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  23. #23
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    Default Re: Crazy subwofer woke me up.

    I've got the exact same problem. Mine is JBL system. It's not that old, maybe 4 years max. It is an auto detect on off system and it's self powered and plugs right into the wall. I recently moved about 2.5 months ago and one morning out of the blue i heard those big "THUMP" and them "zzzzzZZZZZ". Scared the crap out of me, i thought a bomb was about to go off somewhere. I was sleeping and it woke me up. I tried to see if it was interference somewhere so i disconnected the signal cable that was going to it. The sound was still there. So i unplugged it and plugged it back in. The sounds seemed to go away. Funny thing was, the "auto detect feature". The subwoofer was still in the "off" indication. The LED lights on the front were red. They light green when it powers up and receives a signal.

    Then the next day i come home and hear a "thump thump thump thump" coming from upstairs. I went upstairs and surely enough, it was the subwoofer. Same thing. I touched the subwoofer speaker itself and it stopped. It was kind of like resonating. I let go and it started again. It was wierd. So for now, it's just disconnected. I hope there isn't something broken in there. That thing was expensive.
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    Default Re: Crazy subwofer woke me up.

    By the way, the subwoofer is connected via a good cable. So i dont thik it's that. It's never done that before for the 3 years previously that i've had it.
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