# Using a single side of stereo RCA cable - silly question



## thewire (Jun 28, 2007)

I have a pair of stereo RCA interconnects that I am using temporarily to run longer extensions to some subwoofers. The subwoofers seem to sound fine and do a decent job of filling the sound for the rear row however, if I touch the end of each stereo RCA cable that is not plugged in, there is a hum. The hum is only slightly louder if I touch the end that is actually plugged in. Is this because they are in the same shielding? What causes the hum and does this effect the quality of the signal getting to the subwoofers? I have noticed more noise from these cables versus other mono RCA cables but it is does not seem real obvious during any movie watching, and the volume on the subwoofers are turned so far down the hum otherwise is virtually undetectable.


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## eugovector (Sep 4, 2006)

Hmm, let me understand you correctly. You have a standard red/white RCA cable. Let's say both the red ends are plugged in, and both the white ends are unplugged. And when you touch the white end (the other side of which is not plugged into anything) you get a hum? It certainly shouldn't be doing that.


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## jackfish (Dec 27, 2006)

Be sure that the RCA cable is shielded. The cheap stuff and those with long runs may not be.


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## thewire (Jun 28, 2007)

I don't remember exactly what I paid for these but I bought them when I had a car subwoofer installation. One pair was used for the amplifier to the subwoofer in the trunk, and the other was used for the stereo amp to power the channels inside where passengers sit. 

I have used these for running a signal from my soundcard instead of from a DVD player and the same thing occurs. You understood correctly Marshall. I touch the white end and then it hums almost as loud as touching the other end. The big difference is that the exact point where I touch the end that is plugged in, it sounds like tapping on something where as the other end is less pronounced. Using the incorrect side does not get a signal to the device but while it it is connected, touching the wrong side still causes a hum. 

I think that the shielding may be to blame because both red and white connections use the same shielding and are twisted inside. I don't understand why it would be like this. The shielding itself is very poor and placing the cord next to a power cord there are pop and hiss noises. It doesn't happen when I use another stereo RCA cable touching the end not connected and I have never noticed interference before. So this must just be a really bad design for a cable then. 

So then it causes some kind of interference because of the bad design although I might not be able to notice much? I'm not worried as long as this isn't going to harm my subwoofers. 

Here is a photo of one of them. I duct tape the end not connected so that the moving subwoofer does not rattle the end against it or touch any kind of conductor. I warn anyone to stay away from a cable that looks like this. I was obviously taken advantage of during my installation of the car but that was many years ago. I thought the cable looked normal and blue color was nice. :dontknow:


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## eugovector (Sep 4, 2006)

Try switching it out. Even with common shielding, you shouldn't be able to ground it out with your fingers.


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## thewire (Jun 28, 2007)

Switching out does stop the problem, but it is not long enough of a cable that I could use the connections until I can get new ones. Been very busy lately.


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## eugovector (Sep 4, 2006)

Yeah, the cable has to be shorting/poorly designed or something along those lines. The behavior you describe just isn't right (and is very weird, but I'm no expert on groundloops). Time to hit up monoprice.com (I'm sure there are plenty of other cables you could purchase to offset the shipping cost).


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## tonyvdb (Sep 5, 2007)

By looking at your photo I would say that the cable may be sharing the shield and that is why you have the humm but this is not normal practice. Ultimately the shield is common at both ends anyhow so as suggested getting a long mono rca cable would be best.


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## thewire (Jun 28, 2007)

Yes I have actually a bunch of cables I will need to get. Bedroom (with remodel) and media room (ground up) on the way. I will try holding off on the purchase awhile.


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