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    amplifier power output


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    amplifier power output

    Post by baddog1946 on Tue Dec 11, 2012 6:07 pm

    Power Output
    RMS (Root Mean Squared) Power
    RMS measurement is a measure of "power density". It is 0.707 of Peak-To-Peak sine-wave readings so that the roughly 30% deducted can be used to fill "voids" in the sine-wave power envelope of a given sine-wave.
    What does RMS have to do with evaluating an amplifier's performance? Actually an RMS rating has very little meaning in terms of actual dynamic performance of an amplifier, although it has some value when comparing different amplifiers from different manufacturers. If manufacturers quote their RMS values honestly then it is possible to determine which machines are more powerful under RMS test conditions. Unfortunately many manufacturers get very creative in their measurements and all RMS ratings have to be taken at less than face value just in case
    To obtain an RMS rating, a given amplifier is placed in a test jig, attached to a fixed load of a specified impedance, and a signal at a given frequency is increasingly applied until the amplifier cannot produce any more power without "clipping" the sine-wave it is trying to produce. At this point a voltage reading is taken with an instrument calibrated to accurately indicate RMS voltage.
    The waveform can also be measured with a calibrated oscilloscope and a mathematical calculation is used to convert its Peak-To-Peak reading to RMS. Using another mathematical formula, the voltage, in conjunction with the fixed load, produces the RMS rating.
    What has been obtained is only an indication of what power the amplifier can produce continuously at a given frequency with a static and usually non-inductive load connected to other test equipment. This test is far removed from any real world practicality as far as reproducing music is concerned.
    Dynamic Audio Power (DAP)
    Dynamic audio power is a measure of what an amplifier can do in a situation where it is producing actual music into a dynamic load such as a loudspeaker. It is an estimate of how an amplifier can handle any number of frequencies simultaneously into shifting impedances, as loudspeakers can have a number of impedances depending on frequency applied. It is a measure of the reserve power available to produce a smashing low bass note and at the same time producing very subtle high frequency content. It is a measure of what an amp can do in the real world, with real people listening to it, not how it can communicate with a lot of test equipment in a laboratory.
    Dynamic Audio Power usually appears to be greater than RMS in any given amplifier by a factor of two. This is because the amplifier is not totally consumed trying to produce a static frequency continuously as in RMS when a particularly short term heavy load is placed on it such as a powerful bass note as the amp has almost all its reserve at hand to do that job alone, and so can handle the momentary task with relative ease.
    This explains why amplifiers that are rated rather low in terms of RMS have the ability to produce audio results more than the low figures would tend to indicate.
    Which rating is more important? Actually both have merit in evaluating an amplifier. RMS value can be a useful standard by which all manufactured amplifiers power can be compared if manufacturers would tell the truth, or test under exactly the same conditions. Even a poorly crafted amplifier may be able to produce sizable RMS wattage at 1000 Hz but do terribly at 30 Hz where the wattage really counts. The manufacturer will usually quote the RMS at 1000 Hz. To be relevant RMS power ratings should be quoted at about 30 Hz because if the power output is great there it can only be even better everywhere else.
    Dynamic Power is most useful in that it predicts just what the listener will hear in real-world conditions. An amplifier is performing an amazing task trying to reproduce thousands of interacting waveforms, and their harmonics while driving a moving target such as a loudspeaker.

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