How to measure speaker current

Discussion in 'General Electronics Chat' started by PSnetwork, Aug 15, 2013.

  1. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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  2. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Series Ammeter, voltage drop across a series resistor, Clamp on ammeter, etc......
     
  3. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    I Know that... i meant how to calculate it if i dont have the speaker itself.
    only with the speaker info.
     
  4. wmodavis

    Well-Known Member

    Oct 23, 2010
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    That is quite different from what you said in the OP.

    I could only go by what you said not what you say you really meant after the fact.

    And how are we suppose to know just what you know? If you do not provide the pertinent details it's 'by-guess-and-by -gorsh'. My crystal ball is cloudy. Sorry. But I meant to answer what you really meant to ask.
     
  5. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    ok bro just can you tell me how do i calculate the speaker current only with his info sheet?
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
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    At what frequency? Do you know the formula relating power, current & resistance?
     
  7. crutschow

    Expert

    Mar 14, 2008
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    Well "bro", the speaker impedance varies with frequency, as the graph shows. So the current will vary with both the voltage and frequency content of the signal. You divide the signal voltage at a given frequency by the speaker impedance for that frequency. If the signal is more than a single frequency then you must integrate the current for each frequency component to get the total current.
     
  8. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    you have the info below. I think that the currents formula should be, I=P/V.
    anyway i dont sure whats the voltage of the speaker.

    http://www.madisoundspeakerstore.com...ne-wide-range/
     
  9. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Do you know the formula relating power, current & resistance?

    You gave a formula relating voltage, current and power NOT power, current & resistance.
     
  10. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    actually not, im beginner in electronics.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    The speaker voltage is provided by the amplifier driving the speaker with a sound and the voltage value is determined by how loud the sound is.

    What is the purpose of the question? Why are you trying to determine the speaker current?
     
  12. wmodavis

    Well-Known Member

    Oct 23, 2010
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    I= P/R ^1/2

    You gave power = 20 W rms
    On the graph of speaker impedance vs frequency pick a frequency then find the speaker impedance on the graph.

    Then plug those values into the formula I provided above and solve for the current. So if that is really what you want you can calculate it.
     
  13. #12

    Expert

    Nov 30, 2010
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    The simple answer comes from 20 watts, 8 ohms.
    P=I^2R
    20 Watts = current squared times resistance
    20W/8 ohms = current squared
    square root of power over impedance = current
    1.58 amps is the current, continuous and
    from 80 watts peak, current is 3.16 amps.

    This is a very simplified form, but it is enough to try to fit a fuse for the speaker.
    I think 2 amps, slow blow, would be about right, but I'm not the best at fuses.
     
  14. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    im trying to find the speaker current for calculating for how much time the power will be on with 5A/h SLA Battery. i found the solution below, thanks anyway.

    thanks you guys that what i've asked. THANKS.
     
  15. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    No, you haven't. The average current from the battery will probably be less than 5% of what you would calculate from the 20W figure. The 20W value on a speaker is absolutely meaningless for power consumption it's a rating where the voice coil melts.
     
  16. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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  17. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    Sorry but my english is sucks. can you explain in a better way?
     
  18. #12

    Expert

    Nov 30, 2010
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    You have discovered how to calculate the highest amount of power the speaker can survive. You have nearly nothing about how much power the amplifier will send to the speaker.
     
  19. PSnetwork

    Thread Starter Member

    Apr 1, 2013
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    Amplifier is 40W RMS max power. 2 speakers running, each one is 20W, so they will draw something like 40W in full power i guess. Isnt it good?
     
  20. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    No, that's wrong. There is no way they would consume anywhere near 40W average power. You don't get the fact that speakers are rated in peak power and you won't be using anywhere near that power when playing music. I would be very surprised if you used more than 1/2W average power even listening to loud music.
     
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