subwoofer cable question - AVS Forum
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post #1 of 20 Old 12-17-2012, 09:23 PM - Thread Starter
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I buy pretty much all of my cables from monoprice.com and have generally been pretty pleased.

However, their selection of subwoofer cables is pretty sparse.

At around 12 feet, should either of these cables perform differently?

12ft Coaxial Audio/Video RCA Cable M/M RG59U 75ohm

vs.

12ft High-quality Coaxial Audio/Video RCA CL2 Rated Cable - RG6/U 75ohm

It's not the price -- $2 vs. $4 isn't going to break me. I would prefer the thinner, more flexible NOT CL2 rated cable if performance is the same. The only part really throwing me off is the whole RG6 vs. RG59 thing.

My gut says it simply won't matter at this short of a length, but I would like to know if anybody has an opinion or any experience either way. (Or if both of these cables suck, kindly point me in the right direction.)
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post #2 of 20 Old 12-18-2012, 06:50 AM
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Either will work fine.
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post #3 of 20 Old 12-18-2012, 06:55 AM
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Quote:
Originally Posted by woody777 View Post

However, their selection of subwoofer cables is pretty sparse.
That's because there is no difference between a subwoofer cable and any other interconnect. Therefore any interconnect will do.

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post #4 of 20 Old 12-18-2012, 07:05 AM
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It seems like the most important thing to consider with a sub cable is that it is shielded.

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post #5 of 20 Old 12-18-2012, 07:15 AM
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Quote:
Originally Posted by Bond 007 View Post

It seems like the most important thing to consider with a sub cable is that it is shielded.
Shielding is employed to reduce EMI and RFI, which can cause high frequency noise. High frequency noise isn't a concern with a sub. For that matter with the very high input impedance and very low output impedance of most modern devices EMI and RFI tend not to be that much of a problem for full range transmission in the audio bandwidth either; twisted pair interconnects can work just as well as shielded.

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post #6 of 20 Old 12-18-2012, 07:30 AM
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This may be a stupid question because I really don't understand all of that. Can you get EMI or RFI just from having a massive # of cables bunched up behind your entertainment system? I wonder why some people who have humming issues claim that replacing a non shielded cable with a shielded cable has fixed the humming.

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post #7 of 20 Old 12-18-2012, 07:40 AM
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Quote:
Originally Posted by Bond 007 View Post

Can you get EMI or RFI just from having a massive # of cables bunched up behind your entertainment system? I wonder why some people who have humming issues claim that replacing a non shielded cable with a shielded cable has fixed the humming.
It's not impossible. All those coiled cables can become induction fields. Keeping cable runs short and sweet is a good idea. As for hum, that's for the most part indicative of a ground loop, though it's possible for the power transformers in gear to create EMI fields, and that can be picked up by interconnects, creating 60Hz noise. Shielding can help with that. But strictly speaking if that happens it's a gear defect.
As for using shielded cable, it boils down to while it's not always a necessity, sometimes it is, so rather than make things even more confusing for the consumer and seller alike they're pretty much all shielded. For the most part twisted pairs remain a DIY option. Their main appeal is lower capacitance than shielded cable, though IME they don't work any better. However, you do find twisted pairs used a lot in high end boutique cables. Not that it works better, but if you think it will work better (as also applies to silver wire and teflon insulation) it will work better, and you'll find one more justification for being fleeced. Here's one example:
http://www.artisansilvercables.com/construction.htm

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post #8 of 20 Old 12-18-2012, 07:41 AM
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RG6 is better than RG59. You may not notice a difference. The CL2 rated cable is made to go inside the wall. You don't have to put it inside a wall, but that's what it's designed for.

I would defininately recommend using shielded coaxial cable. I've used regular speaker wire with RCA connectors before and in my case, it picked up a 60Hz electrical hum very easily. Switching to coaxial fixed the issue. There's a reason why almost all cable that's labelled as subwoofer cable is coaxial cable.
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post #9 of 20 Old 12-18-2012, 07:54 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

It's not impossible. All those coiled cables can become induction fields. Keeping cable runs short and sweet is a good idea. As for hum, that's for the most part indicative of a ground loop, though it's possible for the power transformers in gear to create EMI fields, and that can be picked up by interconnects, creating 60Hz noise. Shielding can help with that. But strictly speaking if that happens it's a gear defect.

It's not always a gear defect. Your electrical wiring in your house creates a 60Hz electromagenetic field around the wires. The electromagnetic field can induce a current in a nearby wire. Shielding will help ground the field before reaching the inner cable of a coaxial cable which carries the signal. You can easily create the problem by running a regular speaker wire RCA cable in parallel and adjacent to an extension cord.

This isn't as much a problem with normal speakers since they don't emphasize the lower frequencies and also because their signal is already amplified as opposed to a sub which will amplify the hum.
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post #10 of 20 Old 12-18-2012, 08:00 AM
 
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Quote:
Originally Posted by KidHorn View Post

It's not always a gear defect. Your electrical wiring in your house creates a 60Hz electromagenetic field around the wires. The electromagnetic field can induce a current in a nearby wire. Shielding will help ground the field before reaching the inner cable of a coaxial cable which carries the signal. You can easily create the problem by running a regular speaker wire RCA cable in parallel and adjacent to an extension cord.

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post #11 of 20 Old 12-18-2012, 08:15 AM
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I haven't had any hum issues but recently bought a new entertainment stand when I got the new tv so that I could mount the tv instead of using the stand. Mostly for the sake of simplicity and appearance I bought nearly all new cables so that I had the proper lengths. I know it wasn't the most efficient use of money but the spaghetti factory was bothersome. I got 4 HDMI, an HDMI right angle adaptor, 3 coax, 3 ethernet and a coax splitter for about $50. All high quality. Now I have a bagful of spares.

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post #12 of 20 Old 12-18-2012, 08:08 PM
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For long unbalanced (RCA) analog interconnects (and especially for sub-woofers) the most important thing is a heavy shield. It's the low end to end resistance that counts.
A good example is the BlueJeans Cable LC-1 sub-woofer cable.
http://www.bluejeanscable.com/store/subwoofer/index.htm

The co-ax shield won't do much in a strong 60Hz field (but there is fine print).

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post #13 of 20 Old 12-18-2012, 08:32 PM
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Quote:
Originally Posted by Speedskater View Post

For long unbalanced (RCA) analog interconnects (and especially for sub-woofers) the most important thing is a heavy shield. It's the low end to end resistance that counts.
The shield resistance doesn't matter, nor does the core resistance with interconnects, as the current carried is negligible and the load impedance is high.

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post #14 of 20 Old 12-19-2012, 07:32 PM - Thread Starter
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Thanks guys. Lots of good information in this thread.

I guess it just boils down to RG6 vs RG59. I know RG6 is better, but in my application, will I notice any difference?
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post #15 of 20 Old 12-19-2012, 07:36 PM
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No.

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post #16 of 20 Old 12-24-2012, 08:24 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

The shield resistance doesn't matter, nor does the core resistance with interconnects, as the current carried is negligible and the load impedance is high.

It's not about the signal current. It's about the noise and leakage currents.

From page 12 of this Bill Whitlock paper:
http://www.jensen-transformers.com/an/generic%20seminar.pdf

Consider a 25-foot interconnect cable with foil shield and a #26 AWG drain wire. From standard
wire tables (or actual measurement) its shield resistance is found to be 1.0 Ohm. The resistance of
the inner conductor is insignificant and is not discussed here. If the leakage current is 316 uA, the
noise voltage will be 316 uV. Since the -10 dBV reference level for consumer audio is 316 mV,
the noise will be only 20 x log (316 uV ÷ 316 mV) = -60 dB relative to the signal. For most
systems, this is a very poor signal-to-noise ratio. Replacing the cable with Belden #8241F, for
example, would reduce shield resistance to 0.065 Ohm and reduce noise by about 24 dB!

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post #17 of 20 Old 12-24-2012, 08:27 PM
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Quote:
Originally Posted by woody777 View Post

Thanks guys. Lots of good information in this thread.
I guess it just boils down to RG6 vs RG59. I know RG6 is better, but in my application, will I notice any difference?

Remember there are more than 40 different types of RG-6 co-ax and almost as many different RG-59 co-ax's.

So if you pick any co-ax with a heavy braided shield, you should be OK.

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post #18 of 20 Old 12-24-2012, 08:56 PM
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Quote:
Originally Posted by Speedskater View Post

It's not about the signal current. It's about the noise and leakage currents.
From page 12 of this Bill Whitlock paper:
http://www.jensen-transformers.com/an/generic%20seminar.pdf
Consider a 25-foot interconnect cable with foil shield and a #26 AWG drain wire. From standard
wire tables (or actual measurement) its shield resistance is found to be 1.0 Ohm. The resistance of
the inner conductor is insignificant and is not discussed here. If the leakage current is 316 uA, the
noise voltage will be 316 uV. Since the -10 dBV reference level for consumer audio is 316 mV,
the noise will be only 20 x log (316 uV ÷ 316 mV) = -60 dB relative to the signal. For most
systems, this is a very poor signal-to-noise ratio. Replacing the cable with Belden #8241F, for
example, would reduce shield resistance to 0.065 Ohm and reduce noise by about 24 dB!
That could be a consideration if we used foil shield cables with small drain wires for interconnects. But we don't. I don't, anyway, wrong tool for the job. Foil shielding is best when 100% shielding is required, which is the case for radio frequency transmission. For audio interconnects 100% shielding is not required, so copper braid or spiral is used.

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post #19 of 20 Old 12-26-2012, 05:52 PM
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Bruno Putzeys, Jim Brown and Bill Withlock all write about choosing un-balanced interconnects with extra heavy braided shields. So I'll stick with their opinion,.
Thank You

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post #20 of 20 Old 12-26-2012, 09:06 PM
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Quote:
Originally Posted by Speedskater View Post

Bruno Putzeys, Jim Brown and Bill Withlock all write about choosing un-balanced interconnects with extra heavy braided shields. So I'll stick with their opinion,.
Whatever. While I don't ignore the advise of my industry peers...Dennis Bohn is my source of choice where system interconnection is concerned...my own personal experience remains my primary guide.

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