Speaker wire length vs. guage.

Discussion in 'Archived Threads 2001-2004' started by Charles J P, Oct 11, 2001.

  1. Charles J P

    Charles J P Cinematographer

    Joined:
    Aug 19, 2000
    Messages:
    2,049
    Likes Received:
    2
    Trophy Points:
    0
    Location:
    Omaha, NE
    Real Name:
    CJ Paul
    I need to run speaker wire for my surrounds. I plan on going from the receiver out through the drywall into the garage, accross the garage into the basement, and then accross the basement to the back wall of the home theater room. I will be going to the left side of the room from the receiver, which means my right hand side surround is going to need 60' or so of speaker wire since I will be essentiall going around about 60% of the perimeter of the room with my wire. I am going to use UL rated in wall speaker wire, but I was wondering what guage to use. I know accessories4les has some 14-2 for $25 per hundred foot. http://www.accessories4less.com/advscripts/detailpg.asp?sModnum=IXOS-614241-100FT&sPrice=25.00
    e-mail me: cpaul@hometheaterfanatic.com
    My DVD Profiler
    Paradigm Lover
     
  2. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Trophy Points:
    0
    Several speaker sites recommend the following:
    0-10 feet : 16 ga
    10-20 feet : 14 ga
    20-more feet: 12 ga
    Good Luck
     
  3. Scott Bourden

    Scott Bourden Second Unit

    Joined:
    Aug 29, 2001
    Messages:
    457
    Likes Received:
    0
    Trophy Points:
    0
    Bob, wouldn't it be better just to use 12 gauge for all of it then? Is there any particular acoustic reason why they want a smaller gauge (16 and 14) for the shorter runs, or is it just for the price?
     
  4. Allan Jayne

    Allan Jayne Cinematographer

    Joined:
    Nov 1, 1998
    Messages:
    2,404
    Likes Received:
    0
    Trophy Points:
    0
    Smaller gauge wire for shorter distances is only for cost savings, or it may look more discreet due to its smaller diameter.
    If you are doing a lot of speaker runs, 12 gauge throughout may even be cheaper as well as more convenient because you need only one kind of wire.
    More video hints: http://members.aol.com/ajaynejr/video.htm
     
  5. Marty M

    Marty M Cinematographer

    Joined:
    Dec 6, 1998
    Messages:
    2,917
    Likes Received:
    11
    Trophy Points:
    0
    I also think 12 gauge is the route to go for such a long run. I found 12 gauge wire at Lowe's for $.36 a foot. Radio Shack wanted $1 per foot.
     
  6. Brian Corr

    Brian Corr Supporting Actor

    Joined:
    May 10, 1999
    Messages:
    535
    Likes Received:
    0
    Trophy Points:
    0
    You could also use 16-4 and twist 2 conductors together yielding 13 gauge wire. I do this all the time. In wall 16-4 seems to be more readily available than 12-2.
     
  7. Scotty Parish

    Joined:
    May 16, 1999
    Messages:
    43
    Likes Received:
    0
    Trophy Points:
    0
    Brian,
    I would be concerned about the increased capacitance when you twist two insulated conductors together on long runs. The added space, between conductors, increases the capacitance and that would manifest itself in a roll-off of the higher frequencies.
     
  8. Saurav

    Saurav Cinematographer

    Joined:
    Feb 15, 2001
    Messages:
    2,174
    Likes Received:
    0
    Trophy Points:
    0
     
  9. Todd Hochard

    Todd Hochard Cinematographer

    Joined:
    Jan 24, 1999
    Messages:
    2,312
    Likes Received:
    0
    Trophy Points:
    0
    So, tell me:
    How is it that twisted pair wire INCREASES high frequency response in data applications (think Ethernet and Firewire), and yet decreases it in audio applications? I'm curious.
    Todd
     
  10. Bob McElfresh

    Bob McElfresh Producer

    Joined:
    May 22, 1999
    Messages:
    5,182
    Likes Received:
    0
    Trophy Points:
    0
    Scotty: could you be talking about increased IMPEDENCE, not capacitance by twisting wires?
    Capacitance stops low frequencies and then slopes up to let higher frequencies through.
    Impedence lets low frequencies through, then starts reducing the higher frequencies.
    So what effect does twisting the thickly-insulated wires do to the impedence?
    Todd: The twisting of network cable is not to increase the high-frequency response. It's so you can run hundreds of feet of the cable and still get fairly recognizible signals out the other end.
    If you ran the signal wires in parallel, a pulse of voltage on one wire would induce/induct a small blip of voltage in the other. The longer the wire, the larger the blip on the other wire. Eventually, the second wire would look like a logical "1" instead of a "0" and mess things up.
    (Remember those old ribbon-cables that computers used to use to connect to printers? The limit was about 6 feet because of this.)
    Twisting the wires solves this. As the signal induces a blip in the other wire one way, the twist induces the blip in the opposite direction. This push-pull effect allows the signals to travel very far and still be recognizible at the far end.
    Did this help or just confuse?
     
  11. Scotty Parish

    Joined:
    May 16, 1999
    Messages:
    43
    Likes Received:
    0
    Trophy Points:
    0
    The capacitance is between the conductors. Therefore low frequencies are indeed blocked from passing from the one conductor to the other (shorting out if you will). This effect is reduced as the frequency is increased so that as frequency increases more of the signal is passed from one conductor to the other.
     
  12. brucek

    brucek Second Unit

    Joined:
    Dec 29, 1998
    Messages:
    335
    Likes Received:
    0
    Trophy Points:
    0
    Charles,
    60 feet is a fairly long run of speaker wire, although since it's for surround speakers I guess you can't particularly consider these as candidates for critical listening.
    You will indeed gain a little by using 12 gauge instead of the 14 gauge in the resistance department and this will reduce the loss in the cable slightly and increase damping slightly (a good thing), but in a run of this length inductive reactance is your biggest enemy for increasing the total impedance of the connection, particularly at higher audio frequencies.
    Since this a low impedance connection, we can essentially disregard capacitance and the bypass reactance it causes. Capacitance is only a player in high impedance connections such as interconnects between preamps and power amps. It's too small an effect to be considered in a speaker connection.
    Inductance tends not to change much with respect to wire size. Yes indeed, the higher the gauge (smaller wire), the higher the inductance, but it's really an insignificant difference.
    14 gauge will be fine in reasonable length runs. What is reasonable to you though, may be unacceptable to some other audiophile who wouldn't consider anything less than 10 or 12 gauge. They might even make speeches about it. [​IMG]
    It is always a subjective compromise in the choice of how much loss of performance you'll be willing to give up.
    Let me give you some numbers on your 14 gauge run. I'll give you two frequencies of interest.
    100Hz and 20KHz. I won't bore you with the formulas.
    I'll assume a typical 14 gauge speaker wire run at 60 feet with 8 ohm speakers and a solid state amp.
    Typically 14 gauge would have the following specifications.
    14 gauge speaker wire:
    resistance = 2.575 ohms/1000feet
    capacitance = 30 pf/ft
    inductance = 0.20 uh/ft
    So the total resistance of the 60 foot run is: (remember it has to go there and back).
    60 feet = 0.309 ohms
    The total series inductive reactance of 60 foot run.
    60 feet @100Hz = 0.01 ohms
    60 feet @20KHz = 1.51 ohms
    The total bypass capacitive reactance of 60 foot run. (insignificant, I'll ignore these)
    60 feet @100Hz = 884194 ohms
    60 feet @20KHz = 4420 ohms
    So you can see that the big player here at higher frequencies in this low impedance circuit of 8 ohms is the frequency dependant resistance provided by the inductance of the wire. Doesn't really matter too much if you move to 12 gauge. By the way, the 12 gauge will lower that resistance calculation from 0.309 ohms to 0.194 ohms.
    The inductive reactance will tend to roll off your higher frequencies or "roll off" the upper end.
    So what does this all mean. Lets look at what kind of losses you are experiencing at the two frequencies of interest with your 60 foot run.
    *********************************
    @100Hz:
    We add the resistance (0.309 ohms) and the inductive reactance (0.01 ohms).
    Total speaker wire impedance = 0.319 ohms
    Power loss in the cable = 3.83% = 0.169db
    Damping factor drops from 80 to 19 (assuming typical output impedance of power amp at 0.1ohms and 80 damping factor).
    *********************************************
    @20KHz:
    We add the resistance (0.309 ohms) and the inductive reactance (1.51 ohms).
    Total speaker wire impedance = 1.819 ohms
    Power loss in the cable = 18.5% = 0.88db (remember 3 db is half)
    Damping factor drops from 80 to 4. Actually we don't care about damping at these frequencies.
    *********************************************
    So what will you notice here.
    The 14 gauge speaker cable at 60 feet and 100Hz yields a 3.8% loss of signal in the form of heat and has affected system damping by lowering it from 80 to about 19.
    At 20Khz this same run yields an 18.5% loss of signal. That's starting to become significant.
    As I said before, you've created a bit of a low pass filter here and you may notice a slight softening of your upper end. But again, these are surround speakers and you may not care.
    My recommendation would be to go with the 12 gauge if you can find it. If not, the 14 gauge will be fine for this application.
    Good luck.
     
  13. Charles J P

    Charles J P Cinematographer

    Joined:
    Aug 19, 2000
    Messages:
    2,049
    Likes Received:
    2
    Trophy Points:
    0
    Location:
    Omaha, NE
    Real Name:
    CJ Paul
    Wow, thanks for all the comments guys. Some of you have brought up issues that make my head swim, but I will try to digest this all as I make my decision in a few months.
    ------------------
    My Website: http://www.hometheaterfanatic.com
    e-mail me: cpaul@hometheaterfanatic.com
    My DVD Profiler
    Paradigm Lover
     
  14. Vince Bray

    Vince Bray Stunt Coordinator

    Joined:
    Oct 4, 2000
    Messages:
    170
    Likes Received:
    0
    Trophy Points:
    0
    There is a very nice appendix entry in my crest amp book. it lists wire guage, dist, and % loss over the run. No need to guess, just pick how much loss you can stand...
    http://www.crestaudio.com/media/pdf/caman11-25-97.pdf
    it's big, so you might want to right-click and choose 'save target as'. Oh, you'll need adobe, too:
    http://www.adobe.com/products/acrobat/readstep.html
    Assuming 8ohm load (double for 4, interesting)
    With 60', you'll need 14 guage for 3.75% loss
    12 guage for 2.4% loss
    10 guage for 1.5%
    8 guage for .9%
    Vince
     

Share This Page