CATV coax for digital audio

Discussion in 'Home Theater Projects' started by Jason McCallum, Jan 19, 2005.

  1. Jason McCallum

    Joined:
    Dec 14, 2001
    Messages:
    19
    Likes Received:
    0
    Is it possibly to use and get good results using regular cable, e.g. Belden Series 6, for digital audio and video feeds?

    I am talking about regular CATV coax - the stuff that the cable company runs in a house. I want to use it more for powered subs and also for interconnects or patch cords between components.

    Could the cable be terminated with RCA ends instead of F-type connectors? If it works to bring HDTV signals into a sat. receiver, can it be used to send signals to powered subs, interconnects for DVD Audio and even component video? Is the length of runs limited?

    Other then the regular CATV cable is solid core & not as flexible as some more expensive stranded core, why don't more guys use it? Is it going to lose some signal quality?




    POST #1 | Report this post
     
  2. Chu Gai

    Chu Gai Lead Actor

    Joined:
    Jun 29, 2001
    Messages:
    7,270
    Likes Received:
    1
    Ummmmmmm...sometimes. Although the CATV wire is 75 ohms, it's generally copper over steel and that's because the frequencies for CATV start somewhere in the lower 50 MHz range and go up from there. As a result, the majority of the signal rides the surface of the wire due to what's called the skin effect. Since copper is more expensive than steel, and hardly any signal at all goes through the center, cost savings and durability is improved by going that route.
    In the beginning, I said sometimes you can get away with it. Well that's basically in situations where the cable length is very short in which case steel, which is not a great conductor and also not recommended for passing audio signals (20-20k, right?), can be used. The operative word here is short and I wish I could tell you just what short means in meters, but I can't.
    If you're going to start buying connectors, the cost of those far exceeds the cable. My strong recommendation is to go with a 75 ohm stranded cable made of copper. The flexibility is just so, so much better than a single copper conductor. Further, for the lengths you'll likely be running, a few meters, there's no compelling reason to go RG6. RG59 types or what's known as 75 ohm mini coax work just fine. Since the outer diameter of these coaxes are different, you'll have to make sure that the RCA plugs you buy are sized appropriately.
     
  3. Jason McCallum

    Joined:
    Dec 14, 2001
    Messages:
    19
    Likes Received:
    0
    Well, that answers some questions, I appreciate your explanations. I looked at my regular cable & it has the steel inside of the copper. I bought a spool of Liberty serial digital cable & connectors but have used most of it up. This is why I was trying to lean toward regular cable to complete some other longer & shorter cable runs, but I don't think that I will be using it just to save some money now. The thing is, the regular cable is really cheap & the other stuff is not and I would like to find a happy medium. Does Home Depot or the like sell cable that will work properly or do I have to buy the big dollar stuff?
     
  4. Chu Gai

    Chu Gai Lead Actor

    Joined:
    Jun 29, 2001
    Messages:
    7,270
    Likes Received:
    1
    I really don't know if HD or Lowes carries stranded copper coax Jason. There's a bunch of online places where you can buy coax like you're looking for. For example, www.l-com.com carries a variety of coax spools in lengths as short as 100 feet that'll set you back around $20 give or take plus shipping. As an aside, if you're looking to just make audio interconnects, you can always pick up microphone wire over at your local (Guitar Center?) pro audio shop and that'll work great too.
     
  5. JustinG

    JustinG Stunt Coordinator

    Joined:
    May 21, 2003
    Messages:
    114
    Likes Received:
    0
    when my house was wired, RG6 was used for the subwoofer run. At first I was confused, but after finding the F to RCA adapters, it works great. I don't hear any difference between direct rca patch to the sub and thru the coax run.
     
  6. Jason McCallum

    Joined:
    Dec 14, 2001
    Messages:
    19
    Likes Received:
    0
    I checked into L-com.com & the RG59A they sell with the stranded copper center looks like the cable I need. The RG59B & RG6 solid center conductor coax cables they sell are copper covered steel.

    How much does the shielding coverage percentages affect the signal quality or interference? What about braided type only compared to braided & foil covered?

    I was curious about using my CATV coax only for the LFE feed, but the reference to the frequency range 20-20k has me wondering if this coax is still OK for a sub, although I see above that it does work.

    Another thing, what about using Cat-5e for stereo cables? I soldered RCA connectors to the ends of approx. a 35' length to carry stereo signals & it works, but is this OK?
    Will it cause problems for the source that it is coming from? Like load or resistance issues? What about balanced ends or baluns, are they necessary for this type of use?

    Sorry for adding another set of questions, but it looks like I am on to somebody with some good advice!!!
     
  7. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0

    The "good" HD Video rated component cable is about $1.20/ft for the 3 conductor stuff. Compare this to $0.19/ft for CATV coax and you are only paying about 2X the el-cheepo price.

    Call your local electronics stores and see if they have Canare or Belden HD video cable in stock. Or order it from industrial supply houses on the internet.

    Chris White has a good site on how to build your own cables.
     
  8. Jason McCallum

    Joined:
    Dec 14, 2001
    Messages:
    19
    Likes Received:
    0
    The Cat5 that I am using is only for sending a L & R line output audio signal from an Sat. box to a TV input.

    I didn't know if it could be used as is - I soldered RCA ends on the cable and it does carry the signal & sounds OK - but will it cause problems for the line outputs on the STB(higher resistance)?

    I don't have the patience to try using Cat5 to make speaker wire like some have done, I bought a 500' roll of Genesis fine strand 14 gauge wire & installed 2 runs to each speaker.
     
  9. Chu Gai

    Chu Gai Lead Actor

    Joined:
    Jun 29, 2001
    Messages:
    7,270
    Likes Received:
    1
    a) Upon occasion, yes, but it's usually not an issue for well designed equipment.
    b) It's more an issue of the capacitance being driven higher. Flakey high-end stuff and even some mid-fi stuff has problems with large amounts of capacitance. Look in Stereophile's archives for a review of an Adcom amp by Kal Rubinson. He found that by using Alpha-Goertz speaker wire (extraordinarily high capacitance), the amp would't kick on unless a work around was used.
    c) Irrelevent.
     
  10. Jason McCallum

    Joined:
    Dec 14, 2001
    Messages:
    19
    Likes Received:
    0
    I personally would not use Cat5 for speaker wire. I would only be interested in using it for line level (L&R) only. My questions were for using it say from a line out of a cd player to a line in of an amp in a different room, not for speakers.
     
  11. Jason=R

    Jason=R Auditioning

    Joined:
    Dec 15, 2004
    Messages:
    6
    Likes Received:
    0
    Digital audio is a very hard signal to corrupt or degrade. It is a PCM coded digital waveform, and can handle upto 50% LOSS before it has any effect on the quality of the sound. As long as you are using a 75 ohm cable with some type of shielding, you should not have a problem. The only time to be careful and go with good cable is if this is a really long run (>50ft) or the cable is really hard to install (the just in case factor [​IMG] )
     
  12. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0

    I think this would be a bad idea.

    Most L/R interconnects are made from coax. Yes, similar to your CATV coax.

    The idea is this: You have very low-power & voltage signals running along a center wire. But these signals can gather interference by nearby wires (like 60 hz power wires). So you encase the center wire in a 'pipe' make of foil or mesh and you call this the 'shield'. This protects the weak signals on the center wire. This is why we use coax wire.

    Cat5 computer wire ... has different issues.

    The wires are NOT designed to be run anywhere near ANY power wires. They can be gathered into a tight bundle with other wires. And if some other wire nearby happens to be too close and causes interference, the internal wires are twisted so the neighbor wires do a push-pull-push-pull every few inches. This helps throw off the effect of a spot of interference. This, and the fact that digital signals can suffer 30-50% degradation/noise makes this type of wire good for digital signals.

    But Cat5 wire was never designed for the noisy environment behind your entertainment center, or for analog signals.

    Hope this helps.
     

Share This Page