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Why do I get feedback/hum every time I move by subwoofer cable? (Going nuts)

post #1 of 18
4/10/09 at 7:41pm
Thread Starter 
I am using an Audioquest subwoofer cable (shielded) in my home theater. Every time I go behind my TV and happen to move this cable even a tiny bit, my subwoofer starts emitting this loud hum (like feedback sound, which often crescendos increasingly louder). If I move the cable over an inch to a slightly different position, it goes away.

I've gone through different receivers and TVs over the past few years, but this never changes. It otherwise does a beautiful job with sound production (no artifacts, great sound). I hate to replace it unnecessarily, but always wonder if maybe anyone knows the cause (or solution!)

many thanks
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post #2 of 18
4/10/09 at 8:00pm
Quote:
Originally Posted by goosebump View Post

I am using an Audioquest subwoofer cable (shielded) in my home theater. Every time I go behind my TV and happen to move this cable even a tiny bit, my subwoofer starts emitting this loud hum (like feedback sound, which often crescendos increasingly louder). If I move the cable over an inch to a slightly different position, it goes away.

I've gone through different receivers and TVs over the past few years, but this never changes. It otherwise does a beautiful job with sound production (no artifacts, great sound). I hate to replace it unnecessarily, but always wonder if maybe anyone knows the cause (or solution!)

many thanks

I'm no expert, but here are my two cents. It is simply a ground loop. When you touch the cable you are creating a ground loop. Since it is a powered speaker, the sound is emitted. I run into it anytime I move my cable too. Like I said, I'm no expert, but this is what I have come to determine is my issue. Now I just don't touch my sub cable.
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post #3 of 18
4/10/09 at 8:04pm
Thread Starter 
Quote:
Originally Posted by deewan View Post

I'm no expert, but here are my two cents. It is simply a ground loop. When you touch the cable you are creating a ground loop. Since it is a powered speaker, the sound is emitted. I run into it anytime I move my cable too. Like I said, I'm no expert, but this is what I have come to determine is my issue. Now I just don't touch my sub cable.

Thanks for the reply. Actually I should clarify. It's the exact position the cable lies on the floor that causes the hum (not actually the touching of it).
For example, I accidentally move it over an inch, it will hum -- I move it back and it still hums -- so it's just a matter of finding exactly where to lay it on the floor each time until there's no hum.
Always drives me nuts. Anyone else knows, would be much appreciated!
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post #4 of 18
4/10/09 at 9:14pm
Hooooooom! Is that the sound your hearing?
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post #5 of 18
4/10/09 at 9:34pm
Thread Starter 
Quote:
Originally Posted by Raymond Leggs View Post

Hooooooom! Is that the sound your hearing?


Yep, that's pretty much it. (It's kind of like the sound you hear from the speakers when a band is setting up on stage, and there's that very loud constant hooom! sound from the speakers, until they fix it)
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post #6 of 18
4/10/09 at 10:17pm
You got a bad cable or a bad solder joint on the cable, SW, or receiver RCA jack.

Moving the cable causes the ground connection to break and that's causing the hum.

I would start with replacing the cable and go from there...
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post #7 of 18
4/11/09 at 6:07am
Thread Starter 
Quote:
Originally Posted by 11001011 View Post

You got a bad cable or a bad solder joint on the cable, SW, or receiver RCA jack.

Moving the cable causes the ground connection to break and that's causing the hum.

I would start with replacing the cable and go from there...


Thanks. I just tried using a standard RCA cable, and it's the same problem. Also, I just recently replaced my receiver (onkyo 605 with 606), so it's not the receiver. Anything maybe else causing the problem? Maybe I'll try plugging the subwoofer into the same power strip as the receiver (instead of directly into the wall), not sure what else.
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post #8 of 18
4/11/09 at 7:46am
Quote:
Originally Posted by goosebump View Post

Thanks. I just tried using a standard RCA cable, and it's the same problem. Also, I just recently replaced my receiver (onkyo 605 with 606), so it's not the receiver. Anything maybe else causing the problem? Maybe I'll try plugging the subwoofer into the same power strip as the receiver (instead of directly into the wall), not sure what else.


Might be the RCA connector on the subwoofer itself.
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post #9 of 18
4/11/09 at 10:24am
I had a cheap RCA speaker extender cable that made the subwoofer make a realitively quiet HOOOOM! whenever no one was even touching it, so I replaced it with a real thick RCA cable.
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post #10 of 18
4/11/09 at 2:30pm
Thread Starter 
Quote:
Originally Posted by Raymond Leggs View Post

I had a cheap RCA speaker extender cable that made the subwoofer make a realitively quiet HOOOOM! whenever no one was even touching it, so I replaced it with a real thick RCA cable.

The audioquest SW cable I have (sidewinder) is extremely thick, and I've tried replacing it with a basic RCA monoprice cable, and the problem is the same, unfortunately.

Quote:
Originally Posted by arnyk View Post

Might be the RCA connector on the subwoofer itself.

I thought about it, but when I move the cable a millimeter (creating the sound to go off), nothing is really moving at the connection point to the subwoofer.

Not sure what else it could be...
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post #11 of 18
4/11/09 at 2:36pm
Have you actually tried wiggling the cable connectors on both ends?
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post #12 of 18
4/11/09 at 2:57pm
Thread Starter 
Quote:
Originally Posted by whoaru99 View Post

Have you actually tried wiggling the cable connectors on both ends?


Yep, that actually does nothing. (doesn't even cause the sound to start).
It's only if I move the actual cable position.

Could it be the power source to the SW? Maybe try different outlets and/or surge protectors?
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post #13 of 18
4/11/09 at 5:00pm
Quote:
Originally Posted by goosebump View Post

Yep, that actually does nothing. (doesn't even cause the sound to start).
It's only if I move the actual cable position.

Could it be the power source to the SW? Maybe try different outlets and/or surge protectors?

Yes, to both. Have you tried to move a/all power cable near the sub cable to see if that affects the feedback?
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post #14 of 18
4/12/09 at 3:53am
Quote:
Originally Posted by goosebump View Post

Yep, that actually does nothing. (doesn't even cause the sound to start).
It's only if I move the actual cable position.

Diagnosiing prolems like this at this distance can easily be misison impossible.

The symptoms and results of investigations that you have presented is not logical. There has to be something else going on that you are not telling us about.

Get someone with lots of practical experience with audio who can come on-site and help you.


Quote:


Could it be the power source to the SW? Maybe try different outlets and/or surge protectors?

Very, very unlikely. Surge supressors are not designed to address situations like these.

Yes, try other outlets, since it should be easy for you to do.
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post #15 of 18
4/12/09 at 11:44am
By hum, I am guessing you mean 60 Hz? If so, I wonder if there is a power line exactly under the floor where the cable is? Simple common mode pickup.
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post #16 of 18
4/12/09 at 11:44am
Forgot. Easy fix. Move it to where it does not hum and forget about it.
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post #17 of 18
4/12/09 at 11:55am
Thread Starter 
Quote:
Originally Posted by tvrgeek View Post

By hum, I am guessing you mean 60 Hz? If so, I wonder if there is a power line exactly under the floor where the cable is? Simple common mode pickup.

Quote:
Originally Posted by tvrgeek View Post

Forgot. Easy fix. Move it to where it does not hum and forget about it.

I suppose there could be a power line exactly under the floor. As for moving it to where it doesn't hum...not so easy. There is no place where it always doesn't hum (otherwise I would just tape it there). Instead, each time I go behind the tv and happen to touch the wire (moving it a millimeter), it goes off until I find a "new" place to rest it.
Oh well, I've lived with it for 4 years...maybe I can just forget about it.
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post #18 of 18
4/12/09 at 2:38pm
That sounds more like a bad connection. It may not be the cable you are touching, it could be another. Really hard to guess from here. Good luck.
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AVS › AVS Forum › Audio › Audio theory, Setup and Chat › Why do I get feedback/hum every time I move by subwoofer cable? (Going nuts)