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subwoofer problem [1.5ohm+1.5ohm=1.5ohm????]

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  • subwoofer problem [1.5ohm+1.5ohm=1.5ohm????]

    [I read the sticky but I didn't really want to sign up for a more car audio specific forum, so hopefully some one here that reads this will have had some experience or thoughts]

    I just received a used pair of jl 13w7 subwoofers. both have dual 1.5 ohm voice coils. Both wired in series, one reads 3ohms on my multimeter which is what i would expect it to. the other reads 1.5 ohm on the mulitmeter, which is a little odd [i expected 3ohm]. When testing each voice coil individually they both read 1.5ohm. ... tried wiring in parallel and the meter reads .9/.8 ohm. no continuity between terminals and cage [thinking maybe something was grounding out]

    thoughts? I'm kinda at a loss and don't know where to go from here [other than a shop]

    Thanks
    -Red
    MobileThree: in car - Zotac Atom/ION - linuxICE 2.0.2
    --worklog--

  • #2
    You can't reliably measure coil impedance with an ohm-meter. You'd need an actual impedance meter, as resistance will vary with frequency. That said, if you're seeing a difference in the standing resistance of the two 'matched' coils in a dual-coil speaker, there may very well be a problem with it.
    2000 Ford Expedition Eddie Bauer - Bi-Fuel Gasoline/CNG
    Intel D945GCLF2 w/512MB RAM, CL Audigy w/KxProject, M2-ATX, Lilliput EBY701

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    • #3
      They are JL's that is why you have problems, lol
      MY INSTAllS:

      http://www.mp3car.com/vbulletin/show...e-install.html

      http://www.mp3car.com/vbulletin/show...tallation.html

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      • #4
        Originally posted by CraziFuzzy View Post
        You can't reliably measure coil impedance with an ohm-meter. You'd need an actual impedance meter, as resistance will vary with frequency. That said, if you're seeing a difference in the standing resistance of the two 'matched' coils in a dual-coil speaker, there may very well be a problem with it.

        by "standing impedance" do you mean with the woofer unwired [ie not installed], if so that is how i am messuring it [with my standard multimeter]

        each coil individually measures 1.5 ohm, but when wired in series it reads 1.5 ohm, and when wired in parallel it reads .8/.9 ohm.

        is that a valid test? or should i be using an actual impedance meter when the subs are unpowered [my other sub measures as expected, 1.5/coil, 3ohm in series, .75 ohm in parallel]

        Thanks for the help and any insight
        MobileThree: in car - Zotac Atom/ION - linuxICE 2.0.2
        --worklog--

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        • #5
          Ok i think i now understand thank you CrazyFuzzy .. i was under the impression that resistance and impedance were the same, but i get now that that's not exactly true when dealing with AC vs DC and while measuring the resistance of the circuit will not yield what i was looking for [even though the other sub did]
          MobileThree: in car - Zotac Atom/ION - linuxICE 2.0.2
          --worklog--

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          • #6
            Originally posted by red_parchel View Post
            the other reads 1.5 ohm on the mulitmeter, which is a little odd [i expected 3ohm]. When testing each voice coil individually they both read 1.5ohm. ... tried wiring in parallel and the meter reads .9/.8 ohm. no continuity between terminals and cage [thinking maybe something was grounding out]
            That's a bit of a riddle, but I think if the two coils are shorted together somewhere it could be explained.

            Try to see if you have continuity between the two coils. It should be infinity. If not, we probably have an explanation. Measure the 4 possible resistances and report :-).

            Measuring the ohmic resistance is fine for these purposes. The real part of the impedance over the frequency range will only be higher, highest at the resonance frequency.

            http://en.wikipedia.org/wiki/Electrical_impedance

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