Headphones or speakers Ohms

Discussion in 'General Electronics Chat' started by electronewb, May 30, 2012.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    If I understand this well Ohms is resistance therefore an 8ohm speaker would sound louder than a 16ohm speaker. Is that right?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The loudness of a speaker depends on the construction and efficiency of the speaker and the cabinetry.

    But in principle, you are correct. The electrical power dissipated by the speaker for a given voltage output is \frac{V^2}{R}. Hence the 8Ω speaker will consume twice as much power as a 16Ω speaker.

    The electrical power consumed may not translate directly into delivered acoustic power.
    Furthermore, since the perception of sound is logarithmic, the sound will not be twice as loud.
     
  3. electronewb

    Thread Starter Member

    Apr 24, 2012
    260
    3
    Same concept for microphone impedance?

    Sennheiser MKH416 output impedance 800 Ω (high impedance)
    Shure SM-58 impedance 300Ω (low impedance)


     
  4. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    I think you have to take the driving impedance into account.

    You can't assume that the same voltage will be available when driving 8 ohms in a system designed for 16 ohms.

    If the amplifier output was 16 ohms, as if matched to the 16 ohm speakers, then no, 8 ohm speakers would have less power available for producing sound. They might draw greater current but the voltage across the speakers would be so much less that the power at the speakers would be less.

    I'm not all that experienced in practical audio amplifiers, but amplifiers I've seen specs for have had very low output impedances, like in the 2 ohm range, so in that case then yes, 8 ohm speakers would be capable of greater power than 16 ohm speakers (possibly at greater distortion, though).
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
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    And efficiency is a big factor in determining loudness of an acoustical device.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    Not anymore.
    Old amplifiers with vacuum tubes and output transformers had output impedances from 2 ohms to 8 ohms.
    Modern solid state amplifiers do not have output transformers so their output impedance is 0.008 ohms to 0.08 ohms. Then they have a very high "damping factor" to damp the resonances of a speaker.
    Since their output impedance is extremely low then the output power increases and they get very hot and strain the power supply when the speaker impedance is lower than the amplifier was designed to drive.
     
  7. electronewb

    Thread Starter Member

    Apr 24, 2012
    260
    3
    Which one of those microphones would have the most output?


    Sennheiser MKH416 output impedance 800 Ω (high impedance)
    Shure SM-58 impedance 300Ω (low impedance)
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,638
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    Hello,

    It is hard to say wich mic will output the most signal.
    Just try to retrieve the datasheets of both and compare them.

    Bertus
     
  9. electronewb

    Thread Starter Member

    Apr 24, 2012
    260
    3
    But doesn't the higher the impedance the lower signal output? That's what I think but I don't think it's right. Does a 600 ohm phone line consider high or low impedance?
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,638
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    Hello,

    i told you to have a look at the datasheets.
    I have retrieved them and found :
    Sennheiser : 25 mV/Pa output voltage
    Shure : 1.85 mV/Pa output voltage.

    See the attached specsheets.

    Bertus
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    The microphones are completely different:

    1) The Sennheiser mic is a condenser type that has a built-in impedance converter/power supply amplifier circuit inside. Its output impedance is 25 ohms (not 800 ohms) and its minimum terminating impedance is 800 ohms. It is an interference-tube design for extreme directionality (super-cardioid).

    2) The Shure mic is a dynamic type (coil and magnet like a tiny speaker). It does not have an electronic circuit inside. Its output impedance is 300 ohms and it usually feeds a preamp with a 1.2k input impedance. It has ordinary cardioid directionality.
     
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