Cat5 speaker cables and impedance

Discussion in 'Archived Threads 2001-2004' started by John Royster, Jul 27, 2002.

  1. John Royster

    John Royster Screenwriter

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    I was going to try making some cat5 speaker cables since I'm quite familiar with it. Not to brag but I've overseen and designed 100s of miles of fiber optic and copper cable plants. [​IMG]
    Category 5 unshielded twisted pair cable (cat5 utp) has an impedance of 100 ohms. Mismatching impedances produce reflections, meaning a signal sent down a wire can be repeated back to you.
    So my question is doesn't this impedance make cat5 a poor speaker cable at best? Does one WANT a speaker cable with high impedance.
    The reason I'm asking is because I own electrostatic speakers. Most of what I've read says they are unusual with respect to amplifier, cables. Something along the lines of the ESL panel itself presenting some capacitance to the amp.
    What kinds of speaker wires are said to go best with ESLs? I know, I should listen myself but I really don't have the time to audition 6 pairs of wire.
    PLEASE DON'T TURN THIS INTO A "IT DOESN'T MATTER" thread. This linkage is important to my system and I'm curious about the various cap/imp values for speaker wire and thier effect on ESLs.
    Thanks in advance!
     
  2. Chu Gai

    Chu Gai Lead Actor

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    Bet you thought I'd be the last person offering advice, huh?
    first of all, let's forget about the impedence thing as it doesn't apply to the speaker scenario. You're running ML requests with an HK amp. The ML's are a hybrid design with an impedence that I 'think' bottoms out around 2 ohm, maybe a little lower, somewhere I think above 10K. Because they are what they are, a special case of speakers, special things apply...call them exceptions to the rule.
    First your amp should be comfortable delivering power at low ohms (2-1). I don't know if the HK is.
    Second the amp needs to be comfortable with high capacitance cables.
    Third, the preferred setup would be to run two amps, both next to the speakers and let your pre-whatever be in the middle.
    Fourth, your cables. If you did the above, kept the speaker/amp distances short...most likely a 12 gauge regular old crap would do. If though, your amp is in the middle, and your speaker runs are say 10 feet then I'd investigate only two things.
    10 gauge regular old copper (probably get some at installers that do car stereos).
    Preferred scenario...DIY approach...Assuming the 10 foot lengths...the CAT5 stranding technique in order to obtain a low low inductance albeit at a high capacitance cable. Now some amps have issues with this...they can go into oscillation, get real real hot and shut down. If that happens you can try doing the following: put a 0.1 microfarad capacitor in series with a 10 ohm resistor across the speaker terminals. Should be able to get the parts locally and pretty cheap...find some wide shrink wrap and neaten it up.
    Me, i'm not going to get into the electrostatic/ribbon/planar debate. Some people like em, some don't. They do take a bit more (understatement, huh) effort in positioning and often in dealing with other issues such as the nature of the room...back reflections can be an issue...but that's another story. They also place unusual demands on equipment and often connections. Ever thought of getting a pair of Crown amps used? Some have quite amazing power capabilities down in the low range. Active used market in the pro-sound area. Just a thought...let's work with what you have.
    By the way, I'd PM'd you looking for particulars, but you must've missed it.
     
  3. John Royster

    John Royster Screenwriter

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    Actually you were the first person I would EXPECT to reply and I'm quite glad you did. I guess you might understand my dilema.

    First off my current amp is not up to the task. I know this, I hear this. For the record the reQuest manual states they dip to 1.2 ohms at 20K. pretty friggin low. I'd love to see an impedance graph and I may just contact Martin Logan for one.

    So Chu, you're saying given the "special needs" of an ESL that I should keep my speaker cable as short as possible? The way I see it with ESLs is placement comes first, amp come second and cables come a distant third. I have no means to keep my cables short (currently 12 feet) unless I go with mono amps. Problem being is for the money I can get a strong stereo (krell, sunfire...go figure on the sunfire comment but I've heard them with MLs and they sound quite good, or get the innersound) amp instead of monos as much as I'd love 'em.

    Chu, what are you recommending for two scenarios - mono block amps/short cables and what specs should those meet, OR stereo amp with cables 12 or less feet. remember I'm on a budget of 3K for amp and cables, and that is way stretching it considering I'll be buying used.

    -edit- I didn't get the PM, sorry I missed it.
     
  4. Chu Gai

    Chu Gai Lead Actor

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    I know its a headache and a half you've got there John with the ReQuests and getting them setup. I'm sure you've tried a lot of placements John and no doubt have read up on electrostics, dipoles...placements and room treatments. I just ran across the manual for the requests and seems they go down to 1.2 ohms...i'd guess on the high side.
    I think you can do this for less but everyone's got their own idea of amps and such, but spec wise, i'd be looking for something that spec'd out to being able to deliver around 300 or so watts into 2 ohms, figuring there wouldn't be a spec for 1 ohm so it'd likely drop off some. I'd further spec that it could deal with capacitance just for future considerations. I'd get a pair of amps, keep em close, maybe on some nice attractive mimalistic stands in the vicinity of the cable connections to keep in the them of the ReQuests. I'd run a short 12 gauge, low inductance cable. Buy it, make it, its your money and time. The Cat5 is a reasonable approach. Probably at those lengths the extra capacitance wouldn't be an issue for the amp. Interconnects...see my post which should still be here on making them out of belden cable. You want to dbl check that your pre is not going to have a problem driving a long length. Most active pre's don't...Passive ones may likely have issues. While I'd bet that a radio shack gold would likely do, i'd look at the lower capacitance ones. i'm not sure on the capacitance of star-quad geometries...might want to check those out.
    John, the cables won't cost you squat...i'm not going to recommend brands. People will sell you cables that have such specs at preposterous prices. Some won't.
    Over at the asylum...a frightening place for us DBT'ers, i believe there's a forum for electrostatics. Might get some amp recommendations then you can chase down the specs to see if they make sense. I know some use tubes....that'll cost you for sure.
    John, i'd stay away from the center placed amp myself. Maybe you can post here, and on other forums suggestions for amps that'll be in and around what I suggested.
     

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