Subwoofer Hum...Help [Archive] - Audio & Video Forums


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07-30-2010, 01:25 PM
Came home a few months ago with a different cable box(DVR) and a hum started coming from my sub shortly after. I can manipulate the hum by messing with the coax going into the cable box. It just pops on whenever and I can lower it by twisting the cable around. I can get rid of it completely by untwisting the cable partially off the box. I was fine with this til I noticed certain channels were coming in choppy.

I tried plugging the sub in a different outlet and using a cheater plug on both the sub and then the box. The hum is still there. If anybody can offer some help, I'd appreciate it.

07-30-2010, 01:38 PM
Sir, since it started with the new DVR I suggest you contact your cable provider. I suspect that your cable system is not properly grounded. I know how annoying that hum can be, good luck.

Mr Peabody
07-30-2010, 02:31 PM
LJ, good to see you grace us with your presence again :) Is it possible to try a new piece of cable from wall to DVR? Maybe the connectors worked loose when switching out or something. Another thing I'd try would be a filter product that offers a in/out for CATV.

07-30-2010, 08:32 PM
when it doesn't remember the words

Mr Peabody
07-30-2010, 08:40 PM
Rim Shot!!

07-30-2010, 09:52 PM
I can get rid of it completely by untwisting the cable partially off the box.

That is exactly where the problem is. Your cable’s ground (assuming it is grounded properly) does not match house ground in term of voltage, so there is ‘hum” current flowing from higher ground voltage to lower ground voltage.

That is a very common problem which I also suffer from. There are couple of cures. First one would be as Mr Peabody mentioned is to insert a filter into Cable or IC audio path to break the hum current. They are available at radioshck and are called Ground Loop Isolator for $17. It take place of IC from amp to sub, or from cable box to audio components.

Another solution which I use is to separate video system from audio system electrically. Which mean any components that are connected to Cable box will not have any (audio/video) connection to audio system.

07-31-2010, 07:09 AM
Ok I will give those suggestions a try if Comcast says everything is grounded properly. I'll report back once I get this thing figured out. Thanks

08-02-2010, 08:47 AM
Something else to consider is your home's wiring! Try plugging your sub amp into another part of the homes wiring. If your running everything off the same circuit, it can also cause a humming! Start with the obvious and work into the not so obvious!

08-02-2010, 08:56 AM
That is exactly where the problem is. Your cable’s ground (assuming it is grounded properly) ...

...and that's a big assumption. I've never had a problem with speaks/subs but this problem happens frequently with guitars when the input receptacle's wires become detached/frayed. They also display the same dealio in which you can manually "reconnect" the complete chain by movin' stuff around. Check the input on the sub itself.

08-11-2010, 02:23 PM
I checked out my outside cable box and noticed that the ground wire wasn't connected to anything. Turns out it snapped at the end that was connected to the ground rod or whatever it is. I could see the other piece connected to the screw. I just stripped the end, reinserted it and tightened the screw back up. Baam! No more hum.

Thanks for pointing me in the right direction guys! :3:

harley .guy07
08-11-2010, 05:51 PM
Good deal. I figured it was something simple since I have plenty of equipment and I have always been able to trace down problems like this just by tracing back the signal and grounds.

08-12-2010, 03:24 AM
I love the smell of a freshly solved question in the morning... smells like VICTORY!!!!!

Glad they helped you out LJ