Can I use this cable to connect subwoofer? (2 pair 22 AWG stranded, twisted, and individually shielded cable) - AVS Forum
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post #1 of 13 Old 05-23-2013, 08:49 AM - Thread Starter
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My home was wired for surround sound when it was built. And I have this cable in my wall which is located at the right position for my subwoofer, but i am not sure what this cable was laid for.

Here is what i found searching for this cable:

http://libertycable.com/prod_details.php?pitem=22-2P-SHEX-YEL&lincode=&productliname=22-2P-SHEX#tabs-1

It is 2 pair 22 AWG stranded, twisted, and individually shielded cable. I am not sure what this was laid for. (where all the cables run from, I have one of this yellow cable, and 8 black speaker cable and 2 white speaker cable)

I am trying to connect a Denon AVR3312CI receiver to a Polk Audio PSW505 subwoofer.
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post #2 of 13 Old 05-23-2013, 09:03 AM
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It's fine, use two of the conductors, connect the shield drain to the ground wire at one end only.

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post #3 of 13 Old 05-23-2013, 09:26 AM - Thread Starter
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Thanks Bill!

Any idea what the purpose of this cable is? I am thinking it was laid inside wall for a specific purpose.
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post #4 of 13 Old 05-23-2013, 10:21 AM
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Quote:
Originally Posted by AboutMoni View Post


Any idea what the purpose of this cable is?
I assume for a stereo pair of balanced sends.

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post #5 of 13 Old 05-31-2013, 04:58 PM
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That's rather small wire for an RCA return. I would connect the shield drain and one wire to the RCA shell's at both ends.

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post #6 of 13 Old 05-31-2013, 08:10 PM
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Originally Posted by Speedskater View Post

That's rather small wire for an RCA return.
Even 28 ga is plenty, the main reason most cables use a heavier gauge than that is durability.

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post #7 of 13 Old 06-04-2013, 05:40 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Even 28 ga is plenty, the main reason most cables use a heavier gauge than that is durability.

No, the main reason to chose a long co-ax with a heavy shield is to reduce leakage noise current. A good co-ax with a heavy braided shield would be about 25 dB quieter than one with a 28AWG drain wire.

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post #8 of 13 Old 06-04-2013, 08:11 PM
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Quote:
Originally Posted by Speedskater View Post

No, the main reason to chose a long co-ax with a heavy shield is to reduce leakage noise current. A good co-ax with a heavy braided shield would be about 25 dB quieter than one with a 28AWG drain wire.
I think you've been reading too many high end cable advertisements. One of the most effective shields, which is widely employed in cables that work into the gigahertz range, is aluminum foil.

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post #9 of 13 Old 06-09-2013, 05:32 PM
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It's not about gigahertz range, it's about power line related noise.

This from a recent Bill Whitlock seminar:

An Overview of Audio System Grounding & Interfacing 9/4/2012
Bill Whitlock

Leakage Current Effect - A Calculated Example

• A 25-foot cable (foil shield, #26 AWG drain wire) has an end-to-end shield resistance of 1 Ω

• Measured leakage current between the ungrounded devices is 316μA (well under the UL limit of 750 μA)

• From Ohm’s law, noise voltage E = I x R = 316 μA x 1 Ω = 316 μV

• Consumer −10 dBV reference level = 316 mV

• Signal to Noise ratio = 20 x log (316 mV⁄316 μV) = 60 dB

• This is 35 dB worse than an audio CD!

• Same length of Belden #8241F cable, with its shield resistance of only 0.065 Ω, makes S⁄N 84 dB, an improvement of 24 dB!

From a noise perspective, shield resistance is the most important parameter of all.
How many times have you seen it specified on a data sheet or in advertising hype?
I rest my case about clueless manufacturers!

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post #10 of 13 Old 06-09-2013, 08:05 PM
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A cable with only 60dB S/N would be absolutely unusable, but luckily cables that bad are virtually non-existent. And power line noise is not an issue with respect to interconnect cables. Ground loop noise is, but that's another question entirely. Cable resistance is a major issue where speakers are concerned, but as the average sub amp has an input impedance of at least 10k ohms even 100 ohms of interconnect cable resistance is of no consequence. Bill Whitlock knows what he's talking about, so I can only conclude that you misunderstood what he said.
Where the OP is concerned per my instruction in post #2 he'd be using the twisted pair for the signal and ground, relegating the shield to pure shield duty, therefore not carrying any current to begin with.

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post #11 of 13 Old 06-10-2013, 03:45 PM
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Bill, Bill, Bill, the problem is not about shielding air borne RFI interference. The problem is power supply AC line related leakage noise currents. The leakage current will use the unbalanced interconnect return(shield) as a sneak path to get back to it's voltage source. The higher the interconnect's end to end resistance, the greater the noise voltage will be.

A cable with only 60dB S/N would be absolutely unusable
That's way you want to use a cable with a heavy return!

Bruno Putzeys wrote on DIY interconnects:

However, lower frequencies will cause more voltage drop across the resistive component of the shield, and this appears as an error voltage at the receiving end. Take a coaxial cable, take the jacket (sheath) off and dress it in a number of extra layers of shield salvaged from other cables. Hear the sound improve... This addresses the same problem as "mains conditioners" but it does so much more effectively.

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post #12 of 13 Old 06-10-2013, 07:42 PM
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Quote:
Originally Posted by Speedskater View Post

The leakage current will use the unbalanced interconnect return(shield) as a sneak path to get back to it's voltage source.
Not in a properly configured system. If it isn't properly configured you can get ground loop noise, which is unaffected by the resistance of the shield/ground wire. Luckily there are cures, a simple one being only connecting the shield/ground at one end of the interconnect. All is explained here:
http://www.rane.com/note110.html

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post #13 of 13 Old 06-10-2013, 10:48 PM
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Good discussion....
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