Please help with Subwoofer humming - AVS Forum
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post #1 of 7 Old 04-20-2013, 10:19 AM - Thread Starter
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I'll try and keep this as short as possible. I have a HSU Research VTF-2 MK 3 sub and have been using it for about 3 to 3-1/2 years now. I just bought a house and got a true media room setup with 7.1 audio and projector. After about 3 weeks of using this new setup (which can be viewed in my sig) my subwoofer started a very noticeable hum. I called HSU research and they walked me through some troubleshooting steps. They thought it was the RCA cable first, so I replaced it and the humming continued. I replaced my Onkyo TX-NR808 receiver thinking that was the problem and that didn't fix it either.

I bought a Denon AVR-2313CI. so here's what I noticed. I have my XBOX 360, Desktop PC, PS3, WiiU, DirectTV and Denon projector hooked up to the receiver. If I unplug all hdmi cables going in, the hum stops. The only two devices that cause the hum are the DirectTv box and projector. I thought maybe the hdmi cables they were using were bad and tried a different HDMI and it still happened.

I thought maybe it had to do with the electrical so I tried something else. Please note that the subwoofer is only 2 prongs with no ground. I unhooked all hdmi cables to the Reciever and plugged the Subwoofer into a surge protector. When I tried to plug in the DirectTv box HDMI cable in the back of the Reciever to see if the hum started up again, the receiver sparked before I got the cord all the way in. So I took the sub back out of the surge protector and sat there thinking of what else I could try. I decided to move my subwoofer and plug it into a different outlet. With everything hooked back up and the subwoofer plugged into a different outlet, no humming at all. I thought the problem was solved until this morning. I was playing music on my surround setup and the dreaded hum came back again. As long as the sub is on and hooked to th receiver, it has a constant hum. I guess I can try a different sub, but I have a feeling that its not the problem. Maybe it is, but something tells me there's something electrical going on. Please, any help or advice would be appreciated. Thanks

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post #2 of 7 Old 04-20-2013, 11:01 AM
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Quote:
Originally Posted by JewDaddy View Post

I'll try and keep this as short as possible. I have a HSU Research VTF-2 MK 3 sub and have been using it for about 3 to 3-1/2 years now. I just bought a house and got a true media room setup with 7.1 audio and projector. After about 3 weeks of using this new setup (which can be viewed in my sig) my subwoofer started a very noticeable hum. I called HSU research and they walked me through some troubleshooting steps. They thought it was the RCA cable first, so I replaced it and the humming continued. I replaced my Onkyo TX-NR808 receiver thinking that was the problem and that didn't fix it either.

I bought a Denon AVR-2313CI. so here's what I noticed. I have my XBOX 360, Desktop PC, PS3, WiiU, DirectTV and Denon projector hooked up to the receiver. If I unplug all hdmi cables going in, the hum stops. The only two devices that cause the hum are the DirectTv box and projector. I thought maybe the hdmi cables they were using were bad and tried a different HDMI and it still happened.

I thought maybe it had to do with the electrical so I tried something else. Please note that the subwoofer is only 2 prongs with no ground. I unhooked all hdmi cables to the Reciever and plugged the Subwoofer into a surge protector. When I tried to plug in the DirectTv box HDMI cable in the back of the Reciever to see if the hum started up again, the receiver sparked before I got the cord all the way in. So I took the sub back out of the surge protector and sat there thinking of what else I could try. I decided to move my subwoofer and plug it into a different outlet. With everything hooked back up and the subwoofer plugged into a different outlet, no humming at all. I thought the problem was solved until this morning. I was playing music on my surround setup and the dreaded hum came back again. As long as the sub is on and hooked to th receiver, it has a constant hum. I guess I can try a different sub, but I have a feeling that its not the problem. Maybe it is, but something tells me there's something electrical going on. Please, any help or advice would be appreciated. Thanks

There are probably two components of your system that connect to a common ground to create this ground loop. One is the coax on your DirectTV box and I'm guessing the other one is your projector. Most if not all of the projectors that I have worked with have 3 prong power cords.

Probably the easiest way to correct this problem would be a ground isolator on the DirectTV coax:

http://www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M

(typical component of this kind)

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post #3 of 7 Old 04-20-2013, 12:07 PM - Thread Starter
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Originally Posted by arnyk View Post

There are probably two components of your system that connect to a common ground to create this ground loop. One is the coax on your DirectTV box and I'm guessing the other one is your projector. Most if not all of the projectors that I have worked with have 3 prong power cords.

Probably the easiest way to correct this problem would be a ground isolator on the DirectTV coax:

http://www.amazon.com/Viewsonics-VSIS-EU-Cable-Ground-Isolator/dp/B0017I3K9M

(typical component of this kind)


Thanks for the suggestion. I was hoping you would be right but I unhooked everything from the back of my directv box (power, coax and hdmi) the subwoofer is still humming. Could it be a bad sub or something else?

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post #4 of 7 Old 04-20-2013, 12:12 PM - Thread Starter
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Found something interesting. If I jiggle the power cord on the back of my sub, the buzz or hum will either get louder or go away all together. Hmmmmm......

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post #5 of 7 Old 04-20-2013, 01:37 PM
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Originally Posted by JewDaddy View Post

Found something interesting. If I jiggle the power cord on the back of my sub, the buzz or hum will either get louder or go away all together. Hmmmmm......

If jiggling the power cord makes the sub stop working then that would explain why the hum went away.

If the jiggling was lifting the ground pin, then that could break the ground loop.

This device will eliminate ground loops related to the subwoofer:

http://www.radioshack.com/product/index.jsp?productId=2062214



http://www.amazon.com/Audio-Systems-Ground-Isolator-B25N/dp/B000LP4RMG

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post #6 of 7 Old 04-20-2013, 05:18 PM
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Try shielded cable. Search on subwoofer cable at the mono price site. Good references on this subject under Speakers then Subwoofers elsewhere in this forum. I got rid of bad hum using a 3 prong to 2 prong adapter on my power cable. Source of hum is cable coming in from Comcast.

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post #7 of 7 Old 04-20-2013, 08:51 PM
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How will shielded cable break a ground loop?

If "jiggling" the cord changes things it is possible you have a bad power cord, bad socket in the amp, or poor connection inside the amp. I would try a new power cord because that is probably the easiest/cheapest thing to try.

Using a two-prong adapter is what I do for a quick check, but lifting the safety ground is not usually recommended due to safety concerns. I am not sure how valid a concern in practice for a sub, but it could be dangerous.... I would try Arny's suggestions.

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