HOW OFTEN HAVE you seen dinky little speakers labeled 500W or even 1OOOW PMPO? Can these speakers really produce so much sound? Peak Music Power Output (PMPO) or Peak Momentary Performance Output is the maximum power the speaker can momentarily produce, under Ideal conditions, using a specific amplifier before it burns or bursts into flames. The figure is hypothetical, to say the least, and is very popular with sound systems marketers to over inflate specs. A speaker rated at 5000W PMPO obviously attracts attention, but the real power handling capacity of the speaker will be one tenth to one-hundredth of that. Since there is no specified way to measure PMPO, this number should be treated with a fistful of salt. A more realistic measure, though not entirely accurate, is RMS or Root Mean Square. It is the continuous sine wave power that the speaker can handle. Usually, this will be specified at a specific frequency. Look for this number on the speaker, instead of PMPO, since it refers to the amount of power a speaker can handle on a continuous basis. Another closely related figure to output power is Total Harmonic Distortion (THD). All speakers, when they are driven by an amplified signal produce some distortion. This distortion is measured in percentage, and is defined at a specific output power (e.g. 0.5 percent at 50W). Better speakers have lower values THD values, while poorer speakers may quote inflated output without specifying the THD. Evaluate both numbers in conjunction, before you make a decision. You should also know that speakers designed to handle low frequencies (woofers) are often rated for higher power-because more energy is required to produce equivalently loud sound. Tweeters (speakers that handle high frequency sounds) are often specified at lower ratings. The efficiency rating for a speaker is a measure of how well a speaker converts watts of electrical power into watts of acoustical power. Most speaker have a very low efficiency rating between 1 to 10 percent so manufacturers rarely provide this informassive.