My sub woofer turns on randomly and makes noise, please help!

March 22, 2007 6:17 PM

I just moved into a new place and my powered home theater subwoofer is giving me a weird issue. With the entire system off, the sub starts pop-ing in a rapid succession. Like, pop,pop,pop,pop,pop,pop,pop,pop,pop,pop, etc. The only way to kill it is to get up and actually cut the power to it by pulling the plug and then plugging it back in. Anyone have a clue as to what this could be? Is my sub dying? Is the wiring in this place faulty and possibly a hazard? Any ideas? Thanks!
posted by TheDude to Technology (10 answers total)

Do you have anything next to the sub? This happens to me when I leave my cell phone near my speakers.
posted by null terminated at 6:27 PM on March 22, 2007

I had that happen when we moved into our current place, with the powered subwoofer and speakers attached to a computer. Plugging it into a different outlet that was on a separate circuit solved the problem. I can't remember if it was the refrigerator or something else, but there was something on the first circuit that was evidently making the power drop enough to make the subwoofer do funny things. Try different outlets and see if that helps -- there is a chance that your whole apartment / house has fluctuating voltage, which isn't good for any of your electronics.
posted by Forktine at 6:30 PM on March 22, 2007

Sounds like a bad or partially unplugged audio cable on the sub's line-level input.

Could also be that the sub is using level sensning for power control, and the sensitivity is set so high that it's getting false readings from noise in the house wiring. This can happen by inductive coupling between the audio cable and nearby power cables (always keep audio and power as far from each other as possible, and never bundle them together running parallel), or because a ground loop is causing hum in the system.
posted by contraption at 6:38 PM on March 22, 2007

Does yoru subwoofer otherwise work fine? Then I know of a quick and simple, plug&play $27 fix.

This nifty little smart power strip cuts the power to specific marked outlets, when one "switch" device is powered. So, turn off your tv, and the power strip cuts power to your subwoofer as well. No more sounds and you didnt need to buy a new subwoofer!!

As an added bonus, its a real surge suppressor with a $50,000 (i think) equipment warranty, and coaxial cable surge protection. So plug all your stuffs into it, run the main cable line through it, and dont worry about surges or your pop,pop,pop,pop anymore!

Another added bonus .. it saves you money, sinec you dont have to pay for the electric that creates your "pop,pop,pop".. same goes for the stand-by power used when your VCR, DVD player, etc are turned off.
posted by Ryaske at 6:40 PM on March 22, 2007

That's from your wireless router. Your woofer is not shielded.
posted by wfc123 at 8:08 PM on March 22, 2007

As a side note, your tags are worthless for anyone looking for this question again.
posted by klangklangston at 8:28 PM on March 22, 2007

It's from either your wireless router, your computer, or your cellphone. I can make pretty much any active speaker in my house do what you describe by putting my cellphone near it. This includes shielded computer speakers.

So yes, start by checking for radio emitters around your speaker equipment. They might not be nearby; if my mobile phone's oriented in a certain direction, it can set off my boombox's speakers from six feet away.
posted by ardgedee at 6:06 AM on March 23, 2007

When RF devices interfere with active speakers, is it always when the device providing the signal is turned off? If so, it should be possible to add a couple of parts to eliminate the interference, perhaps just a capacitor from signal to ground in the RCA connector.

Maybe it isn't that easy :)

This includes shielded computer speakers.

Shielded, in this case, means additional magnets to cancel out the magnetic fields coming off the drivers, because the magnetic fields can mess up CRT monitors. So, it isn't surprising that it makes no difference to electro-magnetic fields.
posted by Chuckles at 6:48 AM on March 23, 2007

If it's not RF interference, I'd be looking at ground loops. It's a wild-ass theory but it might be possible. When the receiver is on, its output drivers (probably push-pull) are easily able to drain any DC potential that builds up on the center conductor of the sub cable. When the amp turns off, a hypothetical ground potential could rise to the point that it breaks down a transistor, and the resulting sudden discharge is amplified by the sub and makes the popping sound.

Grab a multimeter and measure between the outlets that the various components are plugged into. From any ground pin to any ground pin, you should see no more than a fraction of a volt. Same between ground and neutral. Between any ground/neutral and any hot, you should see 120v RMS.

If you're seeing large ground potentials (over a volt or two) between the ground pins of different outlets, call an inspector or an electrician.

Yeah, it's probably RF though. Does it happen if one end of the wire is unplugged? How about the other end?
posted by Myself at 1:02 AM on March 25, 2007

Just a quick update here:

It happens when the receiver and sub are on, or off, playing music or not. It also occurs with the RCA plugged in or not, at either end.

I'm thinking the internal amp is probably toast....the unit was a refurb to begin with anyway. I think I'll just find a cheap 200watt home amp of craigslist and be done with it.

thanks all.
posted by TheDude at 6:32 PM on July 16, 2007