Wrong pre-wire for subwoofer; humming sound - diyAudio
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Old 15th February 2008, 04:05 PM   #1
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Red face Wrong pre-wire for subwoofer; humming sound

We built a new house, and before the drywall went up, we pre-wired two different rooms for 5.1 surround sound systems. One thing I didn't know ahead of time was that the subwoofer required a different type of cable than regular speaker wire, so we ran 14-gauge speaker wire to all 6 speaker locations.

We bought the Klipsch Quintet III surround sound speakers along with the Klipsch Synergy Sub-10 subwoofer and a Yamaha RX-V461 receiver to power the system.

All 5 speakers in the Quintet III sound great. I mentioned that we failed to run coaxial or RCA cable for the subwoofer, so there was a small complication (there is no turning back as these cables are running all over the dang house). I read lots of different forums out there, and to remedy the problem, I bought two adapters to put an RCA plug on either end of the subwoofer speaker cable. The Yamaha receiver has a single RCA plug output for the subwoofer, so I plugged it in there. The Sub-10 has Red & White RCA plug input for left & right, but the left one says Left/LFE, so I just plugged the single RCA plug into the Left/LFE input. Here is a link to the adapters I bought: http://www.mcminone.com/product.asp?...duct_id=28-580
I plugged in the sub and it is definitely getting power, but unfortunately there is no sound coming out of it except for an obnoxious bass hum. Doesn't seem to be any actual bass coming out at all.

When you reply, keep in mind I'm a female and this is the first time I've ever touched sound equipment, and I have no idea what any circuit boards or power caps or whatever else all technical stuff is going on inside of a subwoofer! I truly appreciate your advice
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Old 17th February 2008, 01:29 AM   #2
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How close are the wires to the electrical power wires in the wall?
I am assuming the speaker wire you used is the standard non shielded type. It sounds like the electrical power running nearby is inducing a 60 hz hum into all of the speaker wires. When you send power through the cables to the 5 speakers and they sound good it is because there is a large "signal" to the speakers and the induced "noise" level is small, you may have heard it called a signal to noise ratio (S/N). The sub on the other hand is receiving what is called a line level signal to its on-board amplifier and then sending the large "signal" directly of the sub woofer inside the box. Line level signals are low voltage so when you induce noise level voltage from the parallel 60hz power lines the amplifier in the sub receives the noise and amplifies it along with the bass signal (low S/N ratio).
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Old 17th February 2008, 02:36 AM   #3
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Thanks for your response.

I'll have to double check the box, but I bought very expensive in-wall rated Audioquest speaker wire, which I would have thought was shielded. In any case, we did take extreme care to ensure that speaker wire was far from electrical wires as possible and never ran the cables along side the wires. Granted, we did run the subwoofer cable to a place on the wall near an outlet so we could plug in the subwoofer, but we came down a separate stud from the electrical wire and then across perpendicular to the place where the wire comes out of the wall. I was hoping all of these precautions would prevent any electrical noise.

Also...if there was electrical noise, shouldn't we still get some bass sound out of the subwoofer? Currently there is no bass at all, just hum.
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Old 17th February 2008, 03:08 AM   #4
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Just hum, I missed that little detail. That is a an entirely different problem.

My first instinct would be a problem with the amp, though don't send it in for test/repair until someone with more electronics knowledge replies.
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Old 17th February 2008, 06:25 AM   #5
Foxx510 is offline Foxx510  Australia
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I'd almost guarantee you have a break in your connections somewhere, so you are only connecting one of the two required wires. Also check that you have wired them the same at each end, so maybe the first thing to do is to take one of the adapters off and switch the wires. Can you post a photo of each end of the wire for us?
Even if you get that working, you will probably find you still get some hum from using speaker wire instead of shielded wire. One possible solution is to use some "baluns" like these.
Good luck.
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Old 17th February 2008, 03:31 PM   #6
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I just carried the subwoofer upstairs to the "media closet" and plugged it in directly to the amp with a 6' Monster cable (instead of using all of the speaker prewire + adapters) and it works fine...lots of bass, no hum. So the receiver and the sub are definitely both ok, and it's something with the connections.

Has anyone ever successfully used a regular speaker cable with RCA adapters to run a subwoofer before? Is the wire in speaker cable even the right stuff to run bass sound through? This is where my greatest lack of knowledge is. If it is possible to use a regular speaker cable, could my problem be that I bought really cheap 24-gauge adapters?
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Old 17th February 2008, 03:40 PM   #7
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pull the jacks away from the walls and check the wiring, btw did you solder or use those screw on connectors? plug the sub in and wiggle the wires to hear if it changes then you will know it is a wiring problem. You might still be picking up noise, you said the boxes were near and outlet, how close? Anyways moving the wires around might give you an indication, let us know what happens. You might need to put a shielded adapter on there.
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Old 18th February 2008, 12:43 AM   #8
JasonB is offline JasonB  Canada
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Location: Chilliwack B.C.
Quote:
Originally posted by shortage32
I just carried the subwoofer upstairs to the "media closet" and plugged it in directly to the amp with a 6' Monster cable (instead of using all of the speaker prewire + adapters) and it works fine...lots of bass, no hum. So the receiver and the sub are definitely both ok, and it's something with the connections.

Has anyone ever successfully used a regular speaker cable with RCA adapters to run a subwoofer before? Is the wire in speaker cable even the right stuff to run bass sound through? This is where my greatest lack of knowledge is. If it is possible to use a regular speaker cable, could my problem be that I bought really cheap 24-gauge adapters?
The problem can't be that fact that you are using speaker wire, functionally it's perfectly fine for a low level signal, There are a few potential issues that could be causing your problems.

The first two is either a short or a break in the wiring somewhere if it has been cut or pinched by a staple, nail, or screw. Either of these two can be tested with a digital multimeter set to the lowest resistance scale quite easily. First dissconnect the RCA connectors from both your subwoofer and amp. Then measure the resistance between the inner and outer conductors of the rca connector at one end, the resistance should not read at all. If you get a measurement it means you have a short in the line somewhere. If it tests ok then have someone short the inner and outer conductors of one of the RCA connectors together with a scrap of wire or metal paperclip, then measure the resistance between the inner and outer conductors at the other end. You should get a low resistance reading, if not you have a break in the line somewhere, or a bad connector.

The other issue may be polarity, the reason it could be an issue is beacuse the outer ring of the RCA connector on most components is connected to the chassis ground. This means that if your polarity is reversed at one end the signal may be shorted due to the fact that the chassis gound of both components are connected together through the power cords and elctrical wiring of your house. Double check and make sure the striped leads from your RCA to speaker wire adaptors are connected to the same color or striped speaker wires at both ends of the run. In other words if the striped lead from the RCA to speaker wire adaptor is connected to the positive speaker wire at one end make absolutely sure that the striped lead from the other adaptor is connected to the positve wire of the speaker wire at the other end. (this assumes the wire from end to end is one piece and has not been joined inside the walls somewhere with the positive and negative leads reversed). It doesn't matter which wire the striped lead is connected to as long as it's done exactly the same at both ends of the run (this also assumes the leads of the RCA to speaker wire adators are both marked the same). If this was the problem I'm surprised your receiver's subwoofer output is still working, but you have already verified that by connecting the sub to the receiver with a shorter cable.

Hope this helps,

Jason
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Old 18th February 2008, 02:51 AM   #9
ciagon is offline ciagon  United States
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If your subwoofer has speaker-level inputs, you could double up the speaker output on your receiver with one set to the main L+R speakers, and the other to the subwoofer.
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