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  • Speakers and ohms

    When you put a meter on a speaker to measure the impedance, will the meter usually read higher or lower than the actual impedance of the speaker?

  • #2
    How far out are you?
    Fwopping, you know you want to!

    VI VI VI: the editor of the Beast!

    There are 10 kinds of people who understand binary. Those who do and those who don't.

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    • #3
      Lower.
      An 8 ohm (impedance) speaker measures around 7.2 (resistance).

      I think shobet is referring to how long the leads are.
      That will also affect the reading.

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      • #4
        I have 4 8 ohms in series parallel, and i get a reading in the 5 ballpark. This is right off the actual speakers and connections - not from a speaker cable.

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        • #5
          Are the speakers connected to the amp?

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          • #6
            Did you zero out your meter before testing?

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            • #7
              Cygnus - not while I was measuring it

              FB - It's a digital meter, but I'll see if there's a way to do it on the fluke

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              • #8
                are you saying that the 8 ohm speakers by themselves are only reading 5 ohms each? I remember getting somewhere in the high 7's for my 8 ohm celestion vintage 30.
                Sam

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                • #9
                  You're doing better than me... I put mine on a multi meter and it reads 21 something on a 16 ohm speaker IIRC. Not a cheap meter, it's a top of the line Fluke. Never figured out what the deal was.

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                  • #10
                    I would disconnect and measure each separated.
                    One or two may be out of spec in the upwards range.

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                    • #11
                      Nominal impedance (what is usually quoted as the impedance of a speaker) and DC resistance (what you read with an Ohmeter) are only loosely related. The actual impedance of a speaker can vary by as much as 1/2-2x across the supported frequency range. 5 Ohms may very well be the specified DC resistance of your speaker.
                      "It's hard to be enigmatic if you have to go around explaining yourself all the time"

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                      • #12
                        Then I shouldn't match the amp setting to the metered reading, right? The speakers are a pair of 8 ohm Boogie Celestions and a pair of 8 ohm vintage 30's.

                        Originally posted by marcus View Post
                        Nominal impedance (what is usually quoted as the impedance of a speaker) and DC resistance (what you read with an Ohmeter) are only loosely related. The actual impedance of a speaker can vary by as much as 1/2-2x across the supported frequency range. 5 Ohms may very well be the specified DC resistance of your speaker.

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                        • #13
                          Originally posted by lhrocker View Post
                          Then I shouldn't match the amp setting to the metered reading, right? The speakers are a pair of 8 ohm Boogie Celestions and a pair of 8 ohm vintage 30's.
                          Yes, you should match it to the impedance, not the DC resistance. I just looked up the specs for the vintage 30, and it says the DC resistance should be 7.3 Ohms. I am not sure about the Boogie Celestions (modified v30s?) but 5 Ohms is probably a little low. You may want to check the wiring of the cabinet, or, as Cygnus suggested, unwire them and measure each speaker individually.
                          "It's hard to be enigmatic if you have to go around explaining yourself all the time"

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                          • #14
                            Thanx guys - wouldn't wanna blow up my head...

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                            • #15
                              The resistance is usually a close reading to impedance like was mentioned and should only be used to get an idea of what you have. Measuring resistance is only one portion of what gives a speaker it's impedance. Four electrical quantities determine the impedance of a circuit: resistance, capacitance, inductance and frequency. Or an easier way to remember it is impedance is resistance plus reactance.

                              Matt

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