Another impedance measured with a voltmeter question. What is going on?

Discussion in 'Amps and Cabs' started by Acid Test, Dec 27, 2010.

  1. Acid Test

    Acid Test Supporting Member

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    I am trying to measure the impedance of a 2x12" cabinet wired in series with 2, 8-ohm speakers. Using a Fluke voltmeter, I am getting 26 ohms.

    I had thought that this type of measurement would yield a result that is somewhat less than the expected 16 ohms and not more. Any suggestions?

    Using the same voltmeter on an 8 ohm 4x12 give 6.4 ohms and on a single 1x12 with an 8 ohm speaker I get 5.8 ohms. All measurements are taken without any signal using a plug in the speaker jack.
     
  2. GuitslingerTim

    GuitslingerTim Member

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    The correct term is multimeter, or ohmmeter, not voltmeter, which is used for measuring volts.

    If the readings are correct, the two speakers are 16 ohms, wired in series.
     
  3. ReginaldBisquet

    ReginaldBisquet Supporting Member

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    Test each speaker separately (and unplugged) with the voltmeter. Perhaps one of the speakers has a broken connection that's making the reading go nuts.

    Otherwise, bring it over and I'll take good care of it. :)
     
  4. Acid Test

    Acid Test Supporting Member

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    Problem is the speakers are each 8 ohms - It is the only impedance Eminence made the Lynch Super Vs in.

    I have two of these 2x12 cabs which are identical in wiring but have different sets of 8 ohm speakers

    Cab 1: Two Eminence Man-O-War speakers, 8 ohms each. Measurement 26.2 ohms

    Cab 2: Two Eminence Lynch Super vs, 8 ohms each. Measurement 26.0 ohms

    Connect the cabs using the parallel in/out yields 9.6 ohms
     
  5. Acid Test

    Acid Test Supporting Member

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    Was hoping to get an answer without having to take them apart. The Redstar cabs have several screws holding the front metal grill to the cab. Each has a rubber spacer you have to line up. Cabs are front mounted but maybe there is a way to get individual measurements opening the back jack plate.
     
  6. ReginaldBisquet

    ReginaldBisquet Supporting Member

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    Then you might have the meter on the wrong setting or the testers plugged into the wrong input. Test the meter on a spare speaker to see if the measurements are close to the speaker rating.
     
  7. tone4days

    tone4days Member

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    make sure you are measuring AC impedance .. not DC resistance
     
  8. Blue Strat

    Blue Strat Member

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    You can't do that with a multimeter.

    There's no way that either
    1) Your meter's battery is good or
    2) those are both 8 ohm speakers or
    3) that your measuring what you think you're measuring (or that your probes are in the right holes in the meter)

    An 8 ohm speaker will measure approximately 6 ohms when using a digital multimeter because it's measuring DC resistance, NOT impedance.

    Start with a new battery and try again. If you're not getting around 12 ohms for the series pair, they're not both 8 ohm speakers. Disconnect them and measure each speaker, one at a time.
     
  9. VaughnC

    VaughnC Supporting Member

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    Something sounds fishy.

    What does your meter read with both probes touching each other? 0.0 ohms? Check a 10 ohm resistor with the meter.
     
  10. tone4days

    tone4days Member

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    perhaps not with some multimeters ... but my fluke can do this ... of course it is an approximation because impedance is a function of frequency ... but it is surely close enough for my purposes
     
  11. SatelliteAmps

    SatelliteAmps Member

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    Which Fluke model is that? Most can measure frequency, but not DC impedance. Haven't heard of one having a DC impedance setting.


    As for the OP, having two incorrectly wired cabinets is the most likely cause here. If you are measuring other things correctly, as you've already stated, then measuring these cab's and having it come up like this means something isn't wired right. Putting two cab's that measure 26.2Ω each in parallel shouldn't get you 9.6Ω, it should get you 13.1Ω. So, that means something is wrong (or the other possibility is that you have either a crossover or a horn involved that is changing what you are expecting to see.)
     
  12. Acid Test

    Acid Test Supporting Member

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    I am almost too embarrassed to say the problem was a low battery. Changed it and all is fine.

    Sorry to bother you guys with this but I do greatly appreciate the responses and learned a lot about these measurements.
     
  13. kevinhifi

    kevinhifi Supporting Member

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    You shouldn't be embarrassed at all. We've all pulled out our hair to discover that the battery is dead, the strings are old, the polarity is reversed, the power is off, or many other really simple things.

    That's what the forum is good for. Glad you got it figured out. My multimeter lets you know when the batter is running low. Maybe yours does too?
     
  14. tone4days

    tone4days Member

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    8060A ...
    [​IMG]
    please don't laugh - it's frikkin' ancient (20+ yrs old) ... i wish it would die so i could replace it with a modern one (auto-ranging, etc) ... it has been absolutely bulletproof
     
  15. Blue Strat

    Blue Strat Member

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    It's the last thing we suspect. Once it's happened one time it moves up on the list.
     
  16. Blue Strat

    Blue Strat Member

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    I've got one of those too. Never noticed an AC impedance function but never really thought to look either.
     
  17. amphog

    amphog Silver Supporting Member

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    My 8060 does not measure impedance.
     
  18. tone4days

    tone4days Member

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    is it not impedance to push the 'AC/DC' button in (for AC) and measure ohms?
     
  19. VaughnC

    VaughnC Supporting Member

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    Impedance is only true for one frequency so, in order to measure impedance, a meter would also need a test frequency selection.
     
  20. tone4days

    tone4days Member

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    yes, of course - just like i mentioned in #10 above <eyeroll> ... but for practical purposes, i have never heard any musician specify a frequency when stating an impedance for a speaker - the average over the useful range is good enough, no? ... lets not be impractically pedantic
     

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