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Measuring speaker ohms

Discussion in 'Amps and Cabs [BG]' started by snoopyjc, Jan 13, 2005.


  1. Does anybody know how to measure a speaker for ohms? My Cerwin-Vega sub is marked 8 ohms, but I contacted the manufacturer and they say it's a misprint and it's really 4 ohms. So, how do I measure it? I'm aware that it has to be measured using an AC input, not DC. I have a VOM and an oscilloscope.

    --joe
     
  2. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    Just use your Multimeter and measure the DC impedance then round up to the nearest standard speaker value.
     
  3. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    An impedance meter will measure the impedance, but most people, even most technicians, don't have one.

    If you use a DC ohmmeter you will measure the DC resistance of the loudspeaker. This is not the same as the impedance, but it can often, but not always, be used to determine the nominal impedance of a loudspeaker: 8-ohm loudspeakers will usually have a DC resistance of about 5 to 6 ohms; 4-ohm loudspeakers will usually be about 2.5 to 3 ohms.
     
  4. You can always build a simple voltage divider with a 600 ohm resistor and a precision 1 ohm resistor. Calibrate the VOM to read 1.0 volts across the 1.0 ohm resistor as a substitute for the speaker load. This will read the speaker impedance value directly off the VOM scale as you sweep through the range.

    This simple procedure is thoroughly documented in Vance Dickason's "Loudspeaker Cookbook".