Using Coax for subwoofer wire? - AVS Forum
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post #1 of 41 Old 08-10-2011, 08:26 AM - Thread Starter
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My prewire in my new house has a coax cable run that they said was for the subwoofer cable. I've never heard of this before, so wanted some advice on whether this is good enough, or should I try and run another cable?

Thanks!
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post #2 of 41 Old 08-10-2011, 08:43 AM
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Quote:
Originally Posted by Roshy View Post
My prewire in my new house has a coax cable run that they said was for the subwoofer cable. I've never heard of this before, so wanted some advice on whether this is good enough, or should I try and run another cable?

Thanks!
Actually, people who have a long run, 40+ feet, will often use coax. For one thing, it is shielded. You just need the little coax to RCA adaptor available at Radio Shack.
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post #3 of 41 Old 08-10-2011, 08:52 AM - Thread Starter
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Cool, I just wanted to make sure it was a decent thing to do, and wouldn't make it sound worse or something like that.
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post #4 of 41 Old 08-10-2011, 07:42 PM
 
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Coax(RG6)=composite video=digital coax(hence why it is called "coax")
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post #5 of 41 Old 08-10-2011, 09:48 PM
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coax is 75ohm just like dedicated subwoofer interconnects.

It'll work just fine.

"Without subs it's just background music - with subs it's the main event!"

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post #6 of 41 Old 08-11-2011, 05:49 AM
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I use it for my "rough-in" pre-wire installs all the time. It works great. There are different types and sizes though (RG59 is also considered "coax"). I personally use Quad-shield RG6 with solid copper core. It's one of the more expensive coax cables available, but you can use it for just about anything.
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post #7 of 41 Old 08-11-2011, 02:10 PM
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How do you compare this wire with other brand names?

http://www.monoprice.com/products/pr...seq=1&format=2

Is it ok to use with this with 3k subwoofers like paradigm sub 15? Is it quad shield?

Is output from receiver to subwoofer analog or digital if these devices allow to use this cable to connect?
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post #8 of 41 Old 08-11-2011, 02:33 PM
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Quote:
Originally Posted by Archaea View Post

coax is 75ohm just like dedicated subwoofer interconnects.

Subwoofer cables and other RCA audio interconnects have no defined characteristic impedance. OTOH, 75ohm coax will work.

Quote:
Originally Posted by sukumar View Post

Is it ok to use with this with 3k subwoofers like paradigm sub 15? Is it quad shield?

Any coax will do.

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Is output from receiver to subwoofer analog or digital if these devices allow to use this cable to connect?

It is analog regardless of the cable used.

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post #9 of 41 Old 08-11-2011, 02:47 PM
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Quote:
Originally Posted by Kal Rubinson View Post

Subwoofer cables and other RCA audio interconnects have no defined characteristic impedance. OTOH, 75ohm coax will work.

That is not what I've read over the years. As I understand it -- it should be:
75 ohm for subwoofer interconnects (just like yellow video composite interconnects as well as digital "coax" digital connections)
50 ohm is standard for L/R (black and red interconnects)

Note that when you look up a "subwoofer" or digital coax cable on most any site they will specifically say 75ohm. If you look up an RCA cable on those same sites they will not specify an ohm rating. Though the two cables do work back or forth and I've tried it and can't tell a difference --- but to my knowledge they are supposed to be different resistance ratings - 75 for Subwoofers and digital connections, 50 ohm for L/R component to component interconnects.

Monoprice cables are really quite high quality. It does not matter the cost of your subs - the cables will more than suffice as will your coax...Coax is likely better shielded than some subwoofer cables -- I've read that many recommend using coax for long runs anyway.

You need a couple of these?
http://www.monoprice.com/products/pr...seq=1&format=2
or these?
http://www.monoprice.com/products/pr...seq=1&format=2

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post #10 of 41 Old 08-11-2011, 02:49 PM
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Quote:
Originally Posted by Kal Rubinson View Post

Subwoofer cables and other RCA audio interconnects have no defined characteristic impedance. OTOH, 75ohm coax will work.

Any coax will do.

It is analog regardless of the cable used.

Thanks for quick reply. I am trying to make sure I am exploiting full potential of high end subwoofer with 8 dollars cable. If I want to go for brand names, they are not even available in stores for 50 feet length. Moreover, price is is three digits.

It seems what you pay is what you get does not apply to any of the cables.
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post #11 of 41 Old 08-11-2011, 02:57 PM
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No analog RCA signal cables (be they full-range or sub-woofer) need to be labeled 75 Ohm. Digital cables are a different ball-game.

Kevin
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post #12 of 41 Old 08-11-2011, 03:04 PM
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Quote:
Originally Posted by Archaea View Post

That is not what I've read over the years. As I understand it -- it should be:
75 ohm for subwoofer interconnects (just like yellow video composite interconnects as well as digital "coax" digital connections)
50 ohm is standard for L/R (black and red interconnects)

There is so much nonsense in the cable business, it is not surprising. I would love for you to show me a technical reference for it. What people sell is what they can convince people to buy.

Quote:


Monoprice cables are really quite high quality. It does not matter the cost of your subs - the cables will more than suffice as will your coax...Coax is likely better shielded than some subwoofer cables -- I've read that many recommend using coax for long runs anyway.

Most high quality RCA audio interconnects are coaxial in structure anyway, so using the term coax to distinguish RF cables from audio cables is not correct.

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post #13 of 41 Old 08-11-2011, 03:07 PM
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Quote:
Originally Posted by sukumar View Post

Thanks for quick reply. I am trying to make sure I am exploiting full potential of high end subwoofer with 8 dollars cable.

Probably. If it doesn't break. The Monoprice cables will do fine.

Quote:


If I want to go for brand names, they are not even available in stores for 50 feet length. Moreover, price is is three digits.

That is an indulgence.

Quote:


It seems what you pay is what you get does not apply to any of the cables.

Depends on what you think you are getting.

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post #14 of 41 Old 08-11-2011, 03:07 PM
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Quote:
Originally Posted by Speedskater View Post

No analog RCA signal cables (be they full-range or sub-woofer) need to be labeled 75 Ohm. Digital cables are a different ball-game.

True.

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post #15 of 41 Old 08-11-2011, 03:10 PM
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subwoofer cable - all labeled 75ohm
http://www.monoprice.com/products/se...+cable&x=0&y=0

digital coax cable - all labeled 75ohm
http://www.monoprice.com/products/se...l+coax&x=0&y=0

RCA cable - none listed as 75ohm
http://www.monoprice.com/products/se...+cable&x=0&y=0

Other AV supply shops all mimic the above example from what I've seen over the years. If it's a myth is perpetuated lots of places...



Quote:
Originally Posted by Kal Rubinson View Post

There is so much nonsense in the cable business, it is not surprising. I would love for you to show me a technical reference for it. What people sell is what they can convince people to buy.

I don't have a reference, if you have one I'll read it. I google searched it because I thought this was common knowledge, but a google search shows conflicting info --- :
http://www.hometheaterforum.com/foru...r-digital-coax

http://www.home theaterspot.com/showtopic.php?tid/104728/

in the second link you'll have to remove the space due to the filter here at avs.

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post #16 of 41 Old 08-11-2011, 03:25 PM
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Quote:
Originally Posted by Archaea View Post

Other AV supply shops all mimic the above example from what I've seen over the years. If it's a myth is perpetuated lots of places...

That's how it becomes a myth. If only source said so, it would merely be an error.

I do not have reference off-hand but my statements are based on basic electrical circuit knowledge. Devices that specify 75ohm impedance (or any other) do so because they provide a matched input/output impedance. So, your cable box or TV has a 75ohm input impedance for the RF source. Same for DACs and other digital devices with coax (S/PDIF) inputs.

The input impedance of typical subwoofers and analog amplifiers is in the 10k-200Kohm range. The source impedance for players, tuners, preamp, etc., that feed these analog devices is, typically, in the 100-1kohm range. The difference between a 75ohm cable and a 50ohm cable is inconsequential.

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post #17 of 41 Old 08-11-2011, 03:34 PM
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I have a multimeter handy...When I get home tonight I'll measure a Monster Cable subwoofer cable, a Monoprice subwoofer cable, and a couple pairs of random RCA type cables. I'll see if there's any difference in any of them. Maybe there isn't...I've never measured before. Now I'm curious...I do understand your point that if the source output and input aren't 50 or 75 ohm, then it doesn't matter what the cable is --- especially if the source or input have such vastly different resistance measurements.

snake oil abounds in this hobby...

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post #18 of 41 Old 08-11-2011, 04:10 PM
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Quote:
Originally Posted by Archaea View Post

subwoofer cable - all labeled 75ohm
http://www.monoprice.com/products/se...+cable&x=0&y=0

If you look at the "subwoofer" cable, you'll see it's also marketed as a composite video and digital coaxial cable. My suspicion is that Monoprice decided it would be easiest to just label the same cable for all three (and it'll work for all three just fine.)

But you could also take half of one of their analog audio cables and use it as a sub cable, too.

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post #19 of 41 Old 08-11-2011, 05:36 PM
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Quote:
Originally Posted by Archaea View Post

I have a multimeter handy...When I get home tonight I'll measure a Monster Cable subwoofer cable, a Monoprice subwoofer cable, and a couple pairs of random RCA type cables. I'll see if there's any difference in any of them. Maybe there isn't...I've never measured before. Now I'm curious...I do understand your point that if the source output and input aren't 50 or 75 ohm, then it doesn't matter what the cable is --- especially if the source or input have such vastly different resistance measurements.

snake oil abounds in this hobby...

Multimeter won't be sufficient. What you will get from the ohm meter is the resistance at 0 hz, not the impedance at audio freq. Plus the freq response will also play a role here. An oscilloscope will do the trick.
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post #20 of 41 Old 08-11-2011, 06:07 PM
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While we're on the subject of cables...

I've never cared to understand what the meaning of the arrows is on a cable. I just blindly plug it in in the direction of the arrows. Does it have something to do with the way it's wound, if it's not solid core? What difference does it really make?

Sorry to hijack, but it seemed sort of applicable, and this thread is already way off topic.


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post #21 of 41 Old 08-11-2011, 07:55 PM
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Multimeter won't be sufficient. What you will get from the ohm meter is the resistance at 0 hz, not the impedance at audio freq.

Correct. And, btw, those 75ohm cables are so rated at frequencies well above the audio range.

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post #22 of 41 Old 08-12-2011, 12:39 AM
 
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I'm pulling a "cardinal sin"...

I use component video cables to run the 6 channel audio from my universal DVD players...
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post #23 of 41 Old 08-12-2011, 07:54 AM
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I'm pulling a "cardinal sin"...

I use component video cables to run the 6 channel audio from my universal DVD players...

Nah.

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post #24 of 41 Old 08-12-2011, 09:09 AM
 
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^^^

You didn't play along with the sarcasm...
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post #25 of 41 Old 08-12-2011, 01:49 PM
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Missed that.

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post #26 of 41 Old 08-12-2011, 02:31 PM
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So funny, I was going to post a question in here about the same cable for my HSU which I need now to make a 50ft run. So the general consensus seems to be it is fine correct.
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post #27 of 41 Old 08-12-2011, 04:45 PM
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This reminds me of a time I went into radio shack about a dozen or so years ago to buy a good yellow video cable. There was a $5 one and a $25 one. I asked the manager what the difference was and she said something about the $5 one not handling DVD signals correctly or some sort of nonsense. Both cables had RG6 printed on them and when I tried to tell her that they were both coaxial cables with a RCA connection at each end, she became angry and started cussing about stupid customers don't know what they're talking about and she's taken training from Radio Shack. I bought the $5 cable and it worked fine with DVD's.

There's a cable place near where I live. I forget the name of it, but they sell any kind of cable you could possibly want and know pretty much everything about cables. I ordered three 100' composite cables because they cost about 10% of what it would cost from anyone else. All they did was run 100' of coax and stick some rca connectors at the end for each wire. They said they use RG6 for pretty much everything audio or video and just attach whatever connector is needed.
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post #28 of 41 Old 08-12-2011, 09:20 PM
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I actually ordered the 75', I might have just made 50 but better to go longer than shorter. I ordered some cable management racks too to organize the mess behind the TV.
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post #29 of 41 Old 08-13-2011, 12:08 AM
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How long is too long for a subwoofer cable? Any guidelines?
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post #30 of 41 Old 08-13-2011, 12:43 AM
 
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Not that I know of. Although I'm sure once you put in a 1/4 mile of coax...

1. Isn't that far enough?
2. There might be some signal loss.

Think about this. Xantech IR control is based on coax. Most major sporting venues/amusement parks use Xantech IR control over coax. How big is the L.A Coliseum? How big is Texas Stadium? How big is Epcot? How big is Disneyland?
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