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Discussion Starter · #1 ·
After a tremendous amount of research and searching to no avail, I am hoping to find some help from the AVS Forum community.


My subwoofer has been producing a very noticable hum. For easier reading, here's the setup of the problem:
  • Both the subwoofer and receiver are double prong, so from what I understand this excludes me from the "ground loop" problem
  • The volume of the hum is directly affected by modifying the volume and Hz controls on the subwoofer
  • The hum only occurs when the receiver it is connected to is off - when the receiver is on, the hum completely disappears.
  • The subwoofer is connected to the receiver via LFE
  • Removing or disconnecting the coaxial cable from the cable box has no affect
  • And perhaps most interestingly, with the subwoofer plugged in without any inputs (just the power cord), there is no hum - however the moment I plug in the LFE cable (even with NO connection on the other end) the hum presents itself. To recap that point, with the subwoofer plugged in to power and the LFE cable going from the sub to absolutely nothing, the hum is produced.


From what I've read, no one has quite had a problem like this. I have my immediate assumptions, but for the sake of not wanting to "taint" the potential results from the community, I would rather not post them. If you have any ideas what might be causing this kind of behaviour, please share your insights!
 

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Discussion Starter · #3 ·
EDIT: Misread what you originally typed. Yes, it is unusual - the subwoofer hums only when the receiver is off. When the receiver is turned on, the hum disappears. I have ordered a new cable from monoprice in attempt to see if that rectifies the issue. Shipping date is apparently the 15th.
 

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Discussion Starter · #6 ·
Thanks for your suggestion, SecretSquirrel. I tried tightening the ends on the cords, and although they were not originally as tight as they could have been, upon tightening the problem still persisted, even without a source on the other end of the cord.
 

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Have you tried a different cable? Might still be an electrical issue if swapping the cable doesn't help.


Try plugging the power from the sub into the same outlet as the receiver and power up the sub with the receiver off. Still hums?




Also, as mentioned, could be an amp issue as well.
 

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Are your sub and AVR on the same power circuit?


Are they on the same phase of the same power circuit?
 

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Discussion Starter · #9 ·

Quote:
Originally Posted by cavu /forum/post/18132507


Are your sub and AVR on the same power circuit?


Are they on the same phase of the same power circuit?

For the sake of isolating the problem I took the sub and lugged it to my second floor on the opposite side of the house and plugged it in up there. Just like downstairs, when plugged in with power itself, it does not produce the hum, but immediately upon plugging in the LFE cable, even without a source, the hum starts right up again.


I think being that I have done this, plus the fact that the receiver and sub are, as mentioned, only double pronged, we can safely rule out any power related issues.
 

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i had a somewhat similar issue that was solved by using rg6 quad shield cable to the sub.
 

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Quote:
Originally Posted by JamesLai /forum/post/18135833


the fact that the receiver and sub are, as mentioned, only double pronged, we can safely rule out any power related issues.

You didn't answer my question: are they plugged into the same outlet, on the same phase??


The fact that there is no safety ground is irrelevant to the sort of symptoms you are experiencing!
 

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Discussion Starter · #12 ·

Quote:
Originally Posted by cavu /forum/post/18136909


You didn't answer my question: are they plugged into the same outlet, on the same phase??


The fact that there is no safety ground is irrelevant to the sort of symptoms you are experiencing!

I believe the fact that I disconnected the sub, moved it to an entirely other part of the house, and plugged it into an outlet on a completely different breaker should answer this question, but if I'm wrong please let me know.
 

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Quote:
Originally Posted by JamesLai /forum/post/18137592


I believe the fact that I disconnected the sub, moved it to an entirely other part of the house, and plugged it into an outlet on a completely different breaker should answer this question

Is the question so hard to answer??
Either they are or they are not. I'm not sure what moving the sub to another room has to do with that.


The sub and the AVR SHOULD BE plugged into the same circuit/phase to eliminate the potential for ground loop effects.


If your AC outlets are split plugs, ie. three wire where the upper and lower sockets are connected to opposite phases, that could cause your problem. If they are plugged into different receptacles on different circuits/phases then that could cause the problem.
 

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Quote:
Originally Posted by cavu /forum/post/18136909


are they plugged into the same outlet?
Quote:
Originally Posted by JamesLai /forum/post/18137869


I have no idea how to answer your question.
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by cavu /forum/post/18137980


For christ's sake, if I have moved the subwoofer to the other side of the house and the problem still persists, do you honestly need me to answer if they're plugged into the same outlet? I assumed since you continued to press the issue that your question somehow did not involve this point.
 

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Quote:
Originally Posted by JamesLai /forum/post/18139040


For christ's sake, if I have moved the subwoofer to the other side of the house and the problem still persists, do you honestly need me to answer if they're plugged into the same outlet? I assumed since you continued to press the issue that your question somehow did not involve this point.

He wants you to plug the sub into the same outlet that your AVR is in.
 

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Discussion Starter · #18 ·

Quote:
Originally Posted by Fanaticalism /forum/post/18141452


He wants you to plug the sub into the same outlet that your AVR is in.

Alright - this is the normal setup of the subwoofer and AVR and the problem is still produced.


As a side note, being that the subwoofer produces the hum completely independently of the AVR it seems this would be a bit of a moot point, but perhaps I'm missing something.
 

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Trust me - it's the cable - it is acting like an antenna picking up the 60 cycles from your house wiring along its lenth.


With the cable disconnected at the receiver you get the hum right? - now disconnect it at the sub and it stops right?


Have you at least tried a different/better cable?
 

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Discussion Starter · #20 ·

Quote:
Originally Posted by TJ7 /forum/post/18141963


Trust me - it's the cable - it is acting like an antenna picking up the 60 cycles from your house wiring along its lenth.


With the cable disconnected at the receiver you get the hum right? - now disconnect it at the sub and it stops right?


Have you at least tried a different/better cable?

Yes, you've described the scenario accurately - I'm hoping you're right!


I have ordered a new cable from monoprice, apparently is arriving today, though perhaps tomorrow is a bit more likely. I didn't specifically order anything with special shielding, though perhaps I should have? This is the item I ordered as a replacement:

http://www.monoprice.com/products/pr...seq=1&format=2
 
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