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Speaker resistance and sound energy

Discussion in 'Electronic Basics' started by M. Hamed, Mar 24, 2013.

  1. M. Hamed

    M. Hamed Guest

    I was reading the ARRL handbook (2010) and on page 4.7 there was this sentence:

    "it can be said that any device that dissipates power has a definitive value of resistance"

    This made me think. I always see speakers modeled 8 Ohms. And this is probably their DC resistance value. But shouldn't the conversion to sound be accounted for somehow since it's a sink on energy delivered?

    I thought maybe an inductance should be added to the model but then an inductance is lossless, so where does the sound producing energy come from?
     
  2. Ken

    Ken Guest

    No.
     
  3. Phil Allison

    Phil Allison Guest

    "M. Hamed"
    ** Not exactly.

    8 ohms ( or whatever) is the"nominal impedance" of the speaker - usually
    measured with a 250 or 400Hz tone.

    The DC resistance of the voice coil is about 80% of that number or about 6.4
    ohms.

    The impedance of most ( bass or full range ) speakers in the range of 250 to
    400 Hz is RESISTIVE too.

    So, we have two resistances that dissipate heat, one the copper wire and the
    other due to losses in the moving suspension, magnet assembly and sound
    radiation.

    Sound radiation accounts for barely 1% of the input power, in most cases.

    A good circuit model for a loudspeaker is not a simple one, it would have
    many inductances, resistances and capacitances involved - plus the
    resistances would each have temperature co-efficient.


    .... Phil
     
  4. M. Hamed

    M. Hamed Guest

    Thank you for the thorough explanation. As it often happens my false assumptions led to false conclusions.

    I remember a couple years ago I created a toy speaker out of magnet wire and a strong magnet. I remember how I carefully wound the coil to measure 8 Ohms DC. How naive I was :)
     
  5. amdx

    amdx Guest

    You trying to start an audiophoolery fight?

    Mikek :)
     
  6. Fred Abse

    Fred Abse Guest

    I like the way they used to (maybe still?) describe horn loudspeaker
    transducers as "motors".
     
  7. Guest

    The "motor" part of a loudspeaker is the linear motor, not the entire
    assembly.
     
  8. Fred Abse

    Fred Abse Guest

    See above
     
  9. Guest

    The cone is part of the transducer (the entire loudspeaker). It is
    not part of the motor.
     
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