Peak vs RMS amplifier power

Discussion in 'Amps and Cabs [BG]' started by alexclaber, Jul 6, 2003.

  1. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    Trying to find out how the peak power compares to the RMS power for various power amps - some of them (like EA) quote peak power, but it's not so obvious for the others.

    The QSC PLX 3002 is rated at 900WRMS/ch@4ohms, and has 2dB of dynamic headroom @4ohms. The Stewart World 2.1 is rated at 650WRMS/ch@4ohms and has 1dB of dynamic headroom @4ohms.

    IIRC continuous peak power is equal to 1.414 x RMS power. I presume that dynamic headroom is the difference between continuous peak power and instantaneous peak power - is that correct? If that is the case, then the QSC peaks at (900x1.414x1.585) 2017W whilst the Stewart peaks at (650x1.414x1.259) 1157W. That means that the QSC has a 2.24:1 peak to RMS ratio, whilst the Stewart has only a 1.78:1 peak to RMS ratio. The EA Iamp 800 claims 800WRMS@4ohms with 2500W peak, at 2.5:1 ratio (though they don't state the impedance that's at).

    Is this correct or am I misinterpreting the specs?

  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Just forget about peak power.
    Everybody measures it is so many different ways, that they're hardly comparable. You usually don't find peak power measurements in the spec files of respectable pro audio companies.
    RMS is reasonably comparable from company to company and is close enough to real-world scenarios that it's useable as a reference.
  3. You are over-interpreting specs, if you ask me.

    There is no such thing as continuous peak power. That's a paradox. If it were peak power, it wouldn't be continuous.

    I think you mean crest factor. Crest factor is the ratio between average power and peak power.

    Processed music signals have a crest factor somewhere around 10 dB, while unprocessed music (single instruments) is 15-20 dB.

    The peak power of an amplifier is a pretty useless spec, because it depends on many factors and is measured under test conditions, usually 1 kHz burst tests. Needless to say, a bass guitar doesn't put out burst tests.

    BTW, what good would 1 or 2 dB of headroom do on a crest factor if 15 dB? And what good will it do if you can't always trust on it? You'd be better off getting a more powerful amp, to begin with, if you want headroom.

    My 2 cents,
    Regardsm, Joris