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Peak watts and watts RMS

Discussion in 'Amps and Cabs [BG]' started by Jaswine85, Oct 21, 2002.


  1. It says the amp im getting is 675 peak and 500 RMS at 2 ohms. What is the difference between peak watts and watts RMS?

    Thanks
     
  2. Different ways of saying the same thing. The difference between peak and rms(root-mean-square) is simply at what point on a sine wave that you make your measurement. Peak, as the name suggests, is the very peak of the wave, where as rms is 70.7% of peak. With that in mind, the actual rms value from 675W peak would be 477W.
     
  3. I always go with the RMS rating. Also look at what frequency and distortion the RMS rating was calculated at. If is say from 20 to 20k at 0.01 distortion then your talking about real clean power. If it is measured at 1k with 1% distortion then this rating is really inflating the wattage figure.
     
  4. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    "Peak" power ratings on amps are mostly useless. Use continuous average (often referred to by the misnomer of "RMS") instead.
     
  5. Thank you!

    I've been having an arguement about this on another forum. One of the participants refuses to believe that RMS is a misnomer when referring to power.
     
  6. Tapp

    Tapp

    Aug 29, 2001
    USA, Mississippi
    RMS=Root Mean Square; it's an AC voltage term not a power term. "Continuous" as Bob stated is the proper term yet RMS has become the "Zerox" of terms for power.

    Tapp
     
  7. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    AC current, too. ;)

    Thanks!
     
  8. I think that continous and RMS have become innerchangable terms like it or not. How many people really know what Horse Power Means? It is ( lb/ft of torque multiplied by RPM's devided by 5252 ) One thing for sure we all agree on is that Peak power is a useless figure.
     
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    For the most part, yes, but not always.

    I once found the Web site of a rather obscure power amp manufacturer that was boasting some incredibly high "RMS" power ratings from fairly small amps.

    Thekey was that they measured maximum power using the old IHF method: a 20 millisecond burst of a 1 kHz sine wave, followed by 480 ms at 1% of full power (-20 dB), repeated every 500 ms.

    They might've used RMS to measure voltage and calculate power, but it sure wasn't continuous! ;)
     
  10. Originally posted by Tapp
    RMS=Root Mean Square; it's an AC voltage term not a power term. "Continuous" as Bob stated is the proper term yet RMS has become the "Zerox" of terms for power.

    Tapp
    And what do you get when you multiply current times voltage? Power my friends, in watts.
    RMS is a true value, but it is not the same as average. Average is calculated by 63.6% of peak.
     
  11. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    True. Thank you.

    And when you multiply RMS voltage times RMS current, you get average power, but not "RMS" power.

    That is true for AC voltage or current, but not power.