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Thread: Measuring PMPO

  1. #1
    Suspended Joe_Carr's Avatar
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    Question Measuring PMPO

    Well I guess I could ask this but why does most speaker companies say the PMPO is just twice as much as the RMS. But some companies say there RMS and there PMPO is like more than twice the power. Like most companies like Cyber Acoustics would say like for example my speakers is 30 watts RMS and 62 watts PMPO. But then some companies I saw on the web that tells about what is PMPO say there are companies that say for example 2 watts RMS and 200 watts PMPO? Do all companies measure differently on there speakers? But most are just double the RMS watts. Even Philips does just double the RMS.

    Have you guys ever seem PC speakers that really say like 300 watts PMPO and only have like 20 watts RMS for example? I never seem that kind of speakers sold in any sites. I only see most speakers are just double the RMS and that's the PMPO.


    This PMPO stuff sounds really interesting to me.

  2. #2
    Suspended Smokey's Avatar
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    Talking about amp power without distorion figure is pretty much useless. If you have high distortion, the power does not matter.

    PMPO in correct term is described as amp's Dynamic Headroom and measured in dB. Most amps (including mine) seem to have 3 dB Dynamic Headroom which as you have noticed come out about twice the RMS rated power. But I also have seen amps with 6 dB DH which mean their PMPO is four times RMS rating.

    3 dB DH = twice RMS power
    6 dB DH = four times RMS power
    10 dB DH = 10 times RMS power

  3. #3
    Suspended Joe_Carr's Avatar
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    So likely the speakers I have seen are the 3 dB Dynamic Headroom since it's twice the RMS. My Cyber Acoustics are rated 30 watts RMS and 62 watts PMPO so I assume it's 3dB Dynamic Headroom.


    When I looked up the word Dynamic Headroom it said
    "the capacity of a system to reproduce loud sounds without distortion"

    Now I thought that if you go around 62 watts it will distort forsure. But does this mean that if the sound is at most at 62 watts then it won't distort and anything higher will distort? I know that music has ups and downs so it will never stay at 62 watts if I have it that loud but if lets say a song stays are same watts the whole time then would it sound clear at 62 watts at most?

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    Listener MikeyBC's Avatar
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    i always thought dynamic headroom was just the ability to handle peaks for very short periods of time....a few milliseconds. Dont think you're 30 watts will sustain 62 watts
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    Until you know the definition of the "peak", it is a meaningless spec in my book.

    RMS (root means square) power has an actual technical definition and the spec is enforced by the Federal Trade Commission (Rule 16 CFR 432). There is no similar set of rules for PMPO or other peak acronyms. Any "peak" specification should be viewed with caution, whether it is used in reference to an amp or speakers. Many times advertising copy is simply an exercise in how far they can push a fairy tale.

  6. #6
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    PMPO doesn't mean anything, period.

  7. #7
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    Quote Originally Posted by mlsstl
    Until you know the definition of the "peak", it is a meaningless spec in my book.

    RMS (root means square) power has an actual technical definition and the spec is enforced by the Federal Trade Commission (Rule 16 CFR 432). There is no similar set of rules for PMPO or other peak acronyms. Any "peak" specification should be viewed with caution, whether it is used in reference to an amp or speakers. Many times advertising copy is simply an exercise in how far they can push a fairy tale.
    +1, but some would say that RMS power is mislabled. In the audio industry, what is called "RMS power" is more appropiately termed as average power. For a pure resistive load, average power is the product of RMS voltage times RMS current [1].
    Here's a wiki quote, "The erroneous term "watts RMS" is actually used in CE regulations." [1]

    PMPO is such an abused term that is it worthless. It is not a regulated term. Anybody can define it any way they want to. Marking's job is to define PMPO such that it gives the biggest number possible.

    The wiki below is highly recommended reading.

    [1] http://en.wikipedia.org/wiki/Audio_power
    Last edited by rakeford; 10-05-2010 at 07:49 PM.
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  8. #8
    Listener MikeyBC's Avatar
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    Quote Originally Posted by rakeford
    The wiki below is highly recommended reading.

    [1] http://en.wikipedia.org/wiki/Audio_power

    of course Spanky will never read this
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  9. #9
    Suspended Joe_Carr's Avatar
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    Well actualy I seen that site before and did read it but I was just wondering if you guys can make it so I understand it better. But when Smokey was saying

    3 dB DH = twice RMS power
    6 dB DH = four times RMS power
    10 dB DH = 10 times RMS power

    What did he actualy meant? I though DH meaning sounds before they distort but maybe I don't quite understand.

  10. #10
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    I'll repeat one more time. There is no standardized measurement protocol for PMPO. Therefore, it is meaningless to compare numbers put out by the various manufacturers.

    It would be like comparing advertised gas mileage between two cars when one car maker tested downhill at 30 mph with a tailwind and the other maker tested at 60 mph, uphill and into the wind. And both published their numbers without telling anyone the test parameters.

    I wouldn't waste anymore time on the PMPO issue if I were you.
    Last edited by mlsstl; 10-05-2010 at 06:42 PM.

  11. #11
    Suspended Smokey's Avatar
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    Quote Originally Posted by Joe_Carr
    But when Smokey was saying

    3 dB DH = twice RMS power
    6 dB DH = four times RMS power
    10 dB DH = 10 times RMS power

    What did he actualy meant? I though DH meaning sounds before they distort but maybe I don't quite understand.
    DH is not sounds before they distort. Dynamic Headroom is reserve power to reproduce music spikes. Amps usually state THD (Total harmonic Distortion) and that should give you an over all idea of amps performance.

    So if you are looking for an amp, look at its watts first, THD% second and then DH (peak) value third. If you get to second step and distorion is high (above 1 %), then there is no need to go to the third step.

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