distortion from sub(s) when plugged in to AC outlet only

default -- Wed, 03/18/2009 - 17:45

Hi Folks
I am perplexed and am hoping that someone might be able to help out. 
I am getting random distortion coming through my powered sub woofer. I originally thought this had to do with my amp, interconnects or line conditioner but have eliminated all those by testing several combinations. 
I am able to reproduce this on two different powered sub woofers and two different amps and with several different interconnects (XLR. etc) . 
I get this noise on both subs and when they are plugged in to a line conditioner or directly into the wall - with nothing else connected to the sub. This tells me its not amp, component or interconnect related.
I can reproduce it on different AC outlets including those with GFIs and on different circuits in the home. 
The sound is nearly always the same. It is not a hum or high level popping but more of a low level garble, generally starting out slow then at times building in intensity and volume. Almost sounds like something is loading up. When I turn the power off of the sub it goes away. 
One of my subs is a Sunfire Tru-EQ. I called support to see if they might have any ideas. They thought a Audio Insulation Transformer might be something to try but from what I am reading these seem to address ground loops. Any thoughts on these? 
I would assume my APC line conditioner with battery backup would regulate power well enough to address AC power issues and I dont think this is a ground loop issue because it is not a hum. 
Can this be some kind of radio frequency interruption?
Any ideas on what it might be, what to test next, how to make it go away?

bwhip (not verified) -- Thu, 03/19/2009 - 12:03

It almost sounds like a grounding issue of some sort. Especially if it does it plugged into all outlets in the house.
One thing you can try is take your sub (or subs) to a neighbors/friends  house and plug it in. If it doesn't hum or have distortion there, then it's probably your house (electrical).
Try it and let us know.

ab7mc2@comcast.net -- Thu, 03/19/2009 - 14:03

   It was also my problem mid 2006 when I begun buying equipment for my home theater. To make the long story short I tried everything I know regarding RFI using my more than ten years experience as a ham radio user. But I failed. What I did, I returned my subwoofer ( no need to mention the brand to protect the reputation of the company). I switch to Martin Logan model Dynamo.  The problem is gone. This model can be down firing. To my curiosity what if I will buy another one because this Dynamo can be connected in series. I place them 15 feet appart and try to adjust several times the level and the phasing according to their distance and according what kind of movie I am watching. Now I am satisfied. And eveytime I want to test my system I used a DVD that I know it will give a good result. One is Denzel Washinton's Dejavu. Note: my DVD player is Denon 3930CI. If you can not return your subwoofer try to borrow from your friend a different sub and try.

Mike19 -- Sat, 03/21/2009 - 14:53

If I understand the problem correctly, you get this noise when one or both subs are turned on, even when they are not connected to your receiver. And, the subs are of differing brands.
It was seem improbable that 2 subs of differing brands would go on the fritz simulataneuosly. The problem sounds like a ground loop, but usually that is caused in subs when something internal gets loose and breaks the subs' ground.  I could see that happening to one sub, but not both (though not impossible).
I think someone already suggested that you take at least one sub to a neighbor's house and see if the noise continues. That might not work, becuase a neighbor's house is probably getting the same power supply as your house.  Maybe take a sub to your office or somplace out of your area and try it there. If, after trying this, the sound is still there, then it must be something in the sub. If you are handy, you might try pulling out the back plate amp and seeing if something metallic has come loose or a wire is touching something it shouldn't . Or you could invest in an anti-hum device (like the Entech Hum X; $90 @ Audio Advisor .com) and see if that helps. There are less expensive hum busters, but I can't recall where.


Kevin Root (not verified) -- Mon, 03/23/2009 - 14:43

 Thanks Mike
I have not yet been able to take this to another home/office but will. One thing that does not make sense is if I have a ground loop producing humm in the home wiring, I would think that my APC line conditioner would address the hum. Is that not the case? 

Mike19 -- Wed, 03/25/2009 - 14:30

Hi Kevin.
I do not believe line conditioners will solve a ground loop. The instructions for many of them state this.
I found the cheaper hum buster if you want to try one: Ground Loop Isolater - $9.80 @ Parts Express on -line. (Part #265-012). Although designed for car audio, it looks like it will work on home audio.


Kevin Root (not verified) -- Sat, 03/28/2009 - 13:34

 Thanks for info on the above ground loop isolator. I was able to get a Entech Hum X at a reasonable price. I plugged it in and unfortunately, no difference. The distortion is still coming through on both subs.  This noise is not a humm, but a low frequency static/ popping kind of sound that will vary in intensity, frequency and duration. 
I am starting to think this is a grounding issue in the home causing this. 
Will take a sub to a neighbors home and test it there but I have a feeling this is going to require an electricians visit to the home. 

ab7mc2@comcast.net -- Sat, 03/21/2009 - 22:37

It's me again. Correction. I should write "regarding RFI and line interference using more than ten years exper... and so on"
And the most important thing, I did not try to open my subwoofer. Thinking they might void the warrantee. I just returned it instead.

Jacob123 (not verified) -- Fri, 03/27/2009 - 04:44

   I think i'm having the same problem, i moved and set my system up the same as my old place, same TV, receiver etc etc.  All i can hear since moving is a loud hum and very little sound comes through.  Tried plugging the sub alone into every plug around the house with same result.  So am i correct when i say the easiest and cheapest way to fix this is with a "Ground Loop Isolator"? and the electronics in my new house suck?  Any help would be appreciated.

kevin root (not verified) -- Mon, 10/05/2009 - 19:13

Hey folks,

After several months I have returned to my origional post (above) about the subwoofer distortion problem. The reason for the long gap is that we have moved. Now in a different home in a different area, I find that I have the same problem as outlined in my origional post.

This is really got me. Two different subs, both getting audible distortion.
I can reproduce this:
on two different subs using two different amps
using various cables and interconnects
plugged into my APC line conditioner or direct to the amps (with or without any audio cables connected)
plugged directly into the wall at various pluggs around the home (now at two different homes)  including a new dedicated circut not sharred by anything else in the home
plugged into the AC with nothing else attached - no amp, no cables.
I have been careful not to cross audio cables & power cables, have disconnected my TV cable and turned off the cable converter box.
I have even had an electrition check the circuts to verify that there is no ground loop.
Can this be a RF issue. Something to do with my wireless network? 

Any suggestions would be greatly appreciated.


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