Why does my sub hum when the reciever is off?

Dannieboiz

This is very annoying, when I had smaller subs it wasn't noticable but it was there. Now that I got the some NHT subs it hums so bad that the house vibrates. Is it my connection or my reciever or sub. I'm using an NHT Subone sub and HK AVR500. My sub are connected with 50ft of composite cables.

TheReaper

From the Polk Audio PSW303/PSW404/PSW505 Owner's Manual:

"Because it doesn’t know the words."

This is what passes for humor in the audio business. Here’s the real answer: If you have any electrical (50/60Hz) hum in your system you’re going to hear it clearly as soon as you hook up your subwoofer. Most hum problems are caused by "ground loops." That is, the electrical grounds of the components in your system are not at the same electrical potential. A very common ground loop source is cable TV. Disconnect the coaxial cable from your TV and/or VCR. If the hum goes away, the cable is the ground loop villain. In that case you need a 75 ohm ground loop isolator. This device attaches to your coaxial cable where it plugs into your VCR (or television). They’re simple to install and usually solve the hum problem. Find 75 ohm ground loop isolators at your audio dealer, Radio Shack stores, or online at http://shop.polkaudio.com.

Ground loops and hum can also be the result of faulty electrical wiring in your home. Consult a licensed electrician to evaluate and, if necessary, repair the AC wiring in your home. Light dimmers also tend to introduce noise into audio systems. Remove them.

If none of our suggestions work for you, contact Polk Audio Customer Service 800-377-7655 (US & Canada), 410-358-3600, 9am-6pm EST, Monday through Friday, or email: polkcs@polkaudio.com.

As you are using an "NHT Subone", call NHT customer service

Dannieboiz

I'm almost 100% certain that it isn't the sub... I think it could be my home wiring, it's a 20 yr old house.

Mike Shelton

You have a ground loop problem.
I had the same problem too.
All you have to do is put a ground loop isolater on the power cord going to your stereo reciever. You should be able to get one from the hardware store or radio shack.
All it is is an adapter plug that goes fron 3 prongs to 2 prongs with a ground wire that is not used and plugs into your wall out- let.
Not using the ground wire is what breaks the ground loop.
I made my own 15" subwoofer with a 350 watt amp and was frustrated with this same issue.
I could not believe it was as easy as it turned out to be to fix.

Dannieboiz

I've never heard of a ground loop isolator that connectors to the power cord. Don't they all go through the RCA cable?

Airplay355

not if its the electricity in your house. this ground isolator changes the 3 prong plug ( the 3rd prong being the ground) to a 2 prong plug and a wire. i think...

Dannieboiz

I think if the purpose of the ground loop isolator is to turn it to a 2 prong, we could have easily chop off the 3rd prong. I sometime have to use these ground loop isolator in car audio in the highs but never subs.

TheReaper

A better solution than a ground wire cheater (not recommended), is to plug both components into the same outlet (provided you are not overloading the outlet).

Hum is frequently caused by antennas, but can also be caused by a marginal component or wire, as well as faulty electrical wiring.

The basic steps for narrowing down where your problem is are below, check if the hum stops as you go along:

- disconnect all attennas (TV/Cable/Satelite/FM) connected to your receiver and any connected component

- disconnect all inputs to your receiver

- disconnect all outputs to your receiver (except the sub)

- plug the sub and receiver into the same outlet

- replace the sub-interconnect with a short interconnect