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Strange Subwoofer Activation - Help, please.


JohnE

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I have a older Klipsch RW-12ii.  Fifteen years and still working fine.  Problem is the past two nights the subwoofer has activated in the middle of the night and sounded like a huge white noise or gurgling sound.  Woke me up immediately.  Ran to the stereo system and everything was fine except the subwoofer was "sounding" off.  I unplugged it, waited, and plugged it back it and the sound stopped.  Everything I check in the system is fine, no problems.  The next night the same thing happened, only at a different time.  What I'd like to know is, can an outside (electrical or radio RF) signal could trip the auto-on feature???  (Or anything else someone could think of to cause this?)  The subwoofer and all of the stereo is plugged into a surge protector.  Nothing else was activated but the subwoofer.  Weird!   Has this happened to anyone else?

 

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While the level of the output sound you experienced is unusual, I would expect it to be equivalent to whatever volume setting on your A/V receiver/whatever was set at, not some arbitrarily loud level like it sounds like you experienced.

 

Here's what I would do to prove/disprove your theory: Disconnect the whatever wiring you're using (speaker/line level/LFE) as the input signal to the subwoofer. Leave power on to the subwoofer however you've got it set; I assume it's Auto-On. Do this for a few nights to confirm it's an input signal that's triggering the problem. If the problem still occurs, then the fault is with the subwoofer itself.

 

If your A/V receiver/whatever is in a Standby mode when this occurs, you may have to actually turn the unit Off instead to solve the issue.

 

Report back with your results.

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 Peter..

 

  The receiver is in stand-by mode, but automatically turns the master volume setting to off when you turn the receiver off (stand-by) which is a heck of a good idea by someone that designed it so you don't forget to turn the volume down before turning the amp back on. The subwoofer (it self) has a volume setting of a bit over half way.  This was an incredibly loud sound.  Worse than white noise.  Anyways, I believe you've got a good idea.  Never thought of unplugging the cable that drives it.  (Just pulled the power to the subwoofer to stop it.)  I'm using a pre-made Monster cable to run the sub (and yes, auto-on).  I'll give this a try over the upcoming weekend and see what happens.  This (as you said) would prove the theory.  A much appreciated answer and will let you know what happens. 

 

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I think Peter's advice will help you troubleshoot the source. I once had a home brew amp with four 15,000 microfarad filter capacitors - huge overkill. The amp would deliver music for 10 seconds after I powered the amp down. But during the next hours I occasionally heard similar noises as they discharged in an unbalanced fashion.

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7 hours ago, JohnE said:

 Peter..

 

  The receiver is in stand-by mode... A much appreciated answer and will let you know what happens. 

 

I had a somewhat similar problem, and discovered this: I run my sub through my Channel B speaker outputs. With the subwoofer set to Auto On, it will go into a low power, Standby mode roughly 5 minutes after I turn off my amp.

 

Sometimes I like to listen to my Heresy's without the subwoofer, so I turn off the Channel B speaker outputs. BUT when I did this, and subsequently turned off my amp, the speakers would NEVER go into Standby mode, as if they were receiving a sufficient drive signal!

 

How could this be-I had turned of the speaker output, just like you would do when listening to headphones so there should be no signal at the speakers, no?

 

So I stuck a voltmeter to the speaker wires at the input to the sub. Sure enough, if I turned OFF the amp, but the Channel B switch was on, I would read X millivolts, but the sub would go into Standby mode as it should. BUT, when I turned off the amp and the Channel B switch was OFF, I would read a much higher millivolt  number. Not enough to hear audio from the sub, but if you stuck your ear near it, you could hear a low level grumbling.

 

I'm thinking either you have an issue with your subwoofer or there is still a signal feeding your sub even with your amp in Standby mode.

 

Post back with your results.

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I have a similar problem with my Klipsch SW350.  It started intermittently and now it does it all the time.  I have disconnected it from the AVR.  I have tried introducing a ground lift, and even a power strip thinking it might be a grounding issues.  I guess it is possible that I'm getting an RF signal from somewhere that is causing this rumbling white noise.  But that seems far fetched.  Any ideas?

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To everyone:

 

   Well, all are interesting answers, but Peter hit the nail on the head.  What happened was the stand-by circuit in the subwoofer was going and poof, it was gone including the amp inside the sub.  Hey, I got fifteen years out of it so I'm not complaining.   These built in amps don't last forever (we can only wish).  Luckily I have a backup sub and I'll use that until I can get a new amp to fix the Klipsch with.   Funny as the backup sub is a 20 year old JBL and I had to re-build it with a new amp.  Now I'll re-build the Klipsch and go from there.  Hopefully Klipsch still has an amp to fit, but if they don't there's tons of these amps on the market, one of them will fit.

 

Bottom line, the auto-on/off was bad and that led to the amp going.  And as Peter stated, there's voltage coming out of the receiver even in stand-by.  So that was enough to trigger the auto-on/off and make the sound.  The amp fried with it.

 

Thank you all for some insight into this problem...

 

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