Is it typical for speaker ohms to measure less than labelled?

Discussion in 'Amp Central Station' started by mercy, Jan 2, 2012.

  1. mercy

    mercy Tele-Meister

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    Hey guys, just learning some hands-on things, like using a multimeter from Harbor-Freight to measure the ohms across a speaker's terminals.

    My EVM12L measures 6.5ish (labeled 8) and the speaker in my old Champ measure 1.6 (not labeled, but "supposed" to be 3.something as indicated on the back of the chassis (it's a 70's silverface champ, stock speaker almost sure.)

    Is this typical? Thanks!
     
  2. Northerntele

    Northerntele Tele-Holic

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    Yep
     
  3. t-luxe

    t-luxe Tele-Afflicted

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    Yes. Your meter is measuring resistance, not impedance.
     
  4. mercy

    mercy Tele-Meister

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    Cool, thanks!
     
  5. blue metalflake

    blue metalflake Doctor of Teleocity

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    I remember hearing a rule of thumb that working impedance was resistance plus 25%
     
  6. gndboy

    gndboy Tele-Meister

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    The impedance is a function of the frequency, so it will be instantaneously variable. "X" ohms, as specified by the speaker manufacturer, is a nominal value. A speaker specified to be nominally eight ohms will show a bit more than six ohms DC on a multimeter. The lower the frequency, the lower the impedance; this is moot because of all the different notes, and all the different harmonic frequencies appearing at the speaker terminals at any one instant. For any given frequency, the impedance is approximately two times pi times the frequency (in Hz) times the inductance of the voice coil (in Henrys). Too theoretical.
     
  7. printer2

    printer2 Poster Extraordinaire

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    Ohms RMS? :lol:
     
  8. Jakeboy

    Jakeboy Tele-Afflicted

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    I have a beat old EV SRO that is an 8 ohm model. It sounds killer. It reads 8.3 ohms so I am guessing it is WAY broken in. It is an old player that rocks in an 8 ohm installation. It freaked me out a bit when I first put a meter on it as I was expecting a DC resistance of 6.5-6.7....
     
  9. ASC67

    ASC67 Friend of Leo's

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    For kicks I tried to measure a couple of my spare speakers that I know are 8 Ohms and I'm getting a reading on my meter of like 1 Ohm. I know the speakers work and I know my meter works because I just measured a pickup. Maybe I'm doing it wrong. What should my meter be set to.
     
  10. megafiddle

    megafiddle Former Member

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    It should be set to the lowest range.

    So if it had 200, 2K, 20K, 200K, etc, set it to 200.

    Also, take a reading with the probes shorted to each other. It may not be zero.
    If it isn't zero, subtract that amount off the speaker measurement. So if the probes
    themselves read 0.8 ohms, and the speaker measured 6.6 ohms, subtract the 0.8
    off of the 6.6. Actual reading would then be 5.8 ohms.

    Make sure you have good contact with low ohm measurements. Twist the probes
    a little and try different spots to make sure you are getting the lowest possible
    reading.
     
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