How can I determine a speaker's impedence (ohms)?

Discussion in 'Archived Threads 2001-2004' started by Ed O, Nov 27, 2001.

  1. Ed O

    Ed O Agent

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    Will a reading from an Ohm meter work? If not, how can I determine this info? The spec label is missing from the speaker in question.

    Thank you.
     
  2. Andy_S

    Andy_S Second Unit

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    No, an ohm reader won't work. The impedence of a speaker is not the same as a resistor. I'm not sure exactly how it's measured, but I believe it's some sort of average. The higher the frequency passed through a coiled wire, the higher the impedence. Since an ohm meter measures resistance by passing a flat DC current through the leads, it would read almost 0 impedence*.

    *note: This is very basic electronics so I'm sure I'm not 100% correct on this.
     
  3. Saurav

    Saurav Cinematographer

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  4. PatrickM

    PatrickM Screenwriter

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    You'll need something like an audio analyzer or a audio frequency network analyzer in order to read the impedance of a speaker.

    Patrick
     
  5. jeff lam

    jeff lam Screenwriter

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    Are you talking about a speaker system(mid/tweet/x-over) or just a single driver?

    From my experiences and experiments if you use a ohm meter for a single driver, you will get the DC resistance. I usually found 4ohm speakers to have a 3.4 - 3.8 ohm DC resistance. If you want to measure a speaker system, the meter won't show anything.
     
  6. Norm Strong

    Norm Strong Stunt Coordinator

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    Yes, you can use an ohmmeter. The DC resistance of a speaker is usually around 80% of the minimum AC impedance.
     
  7. Danny Owens

    Danny Owens Agent

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    IT depends how accurate you want to be and what information that you want to gain from the measurements. To do it properly for the entire spectrum, you would need a volt meter, ammeter, and some type of tone generator. Since a passive crossover is somewhat of an unpredictable dynamic load, it is hard to determine impedence without factoring in reactance.

    What I have done is place a volt meter across the load and an ac ammeter designed to be in series with the load. An amprobe is not accurate enough since the amprobe is a current transformer with on hell of an inductive lag. With a constant volume, source a signal of known frequency to the amp. At the speaker, measure the voltage and the current.

    Divide the voltage by the current and that gives you the impedence of the speaker at that frequency. If you have gone that far, you may want to go ahead and plot the impedence for the entire spectrum based on ISO centers.

    Like anything else in the audio industry, speaker impedence ratings are not standardized. Some manufacturers rate "nominal" which simply means average; but, they dont tell you at what points in the spectrum the measurements are taken to come up with an average. Other speakers are impedence rated at a given frequency; typically 1khz.

    Danny
     
  8. Ariel

    Ariel Stunt Coordinator

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    it is not possible to measure the impedance of the speaker using conventional equipments. it is the summation of the resistive, capacitive and inductive reactance on a given frequency. to find out this info, try to contact the speaker manufacturer. some manufacturers have this information and some reviewers also post this info on their equipment reviews.
     

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