Hi Fi Jargon Buster – Audio Power, RMS power, watts RMS, Peak Power
Audio power is the electrical power transferred from an audio amplifier to a loudspeaker, measured in watts. The power delivered to the speaker and the speakers sensitivity is what determines the actual audio power level delivered by the speaker. The amount of electrical energy that a system (Amplifier & Speakers combined) can convert to to actual sonic energy is seen as one of the more important manufacturers specifications as regards audio equipment statistics on would think that with this in mind there would be one single well defined and understood ratings system. But due to the differing needs of audio professionals and of audio companies marketing this is unfortunately not the case.
RMS vs PMPO (or Peak Power)
RMS Power refers to Root-Means-Square power. To get a rough figure for RMS power, you can multiply the Peak Power Rating x 0.6 EG: if an amplifier is rated at 100 watts peak power, the approximate RMS power would be 60 watts. The RMS rating is a measure of continuous power in watts and the higher the RMS power means the device is either able to provide or accept the specified power over a significant length of time.
Some manufacturers use the more impressive PEAK POWER ratings in their specifications. Using Peak Power (PMPO) ratings when assessing a music product is a bad idea as Peak Power does not reflect a a systems capabilities in normal use. PMPO is a measure of the maximum power that can be handled for a very short period of time. Speakers and amplifiers should always be compared via the RMS power ratings as these are far more reliable and far more likely to have a genuine impact on the sonic results you get..
If you have a system with a speaker that an RMS rating of 100 watts and the amp is similarly rated at 100 watts RMS, the speaker and amp should theoretically be perfectly matched and so result in an ideal performance from both products.
Real World Power and loudness
Perceived “loudness” varies logarithmically with output power a change in output power produces a much smaller change in perceived loudness. This is not to say that bigger speakers can produce more sound with less power but instead that larger speakers can generally take and output more initial power and thus need less amplification to produce the same perceived power output level. This is one reason why the speakers in a system are so important to overall sound quality. The best measure of a systems power is maximum loudness before clipping, in decibels (dB).
Remember as a rule of thumb: more speaker+less amp. = same “loudness” + less distortion
Dodgy Industry Practices to be Aware of
It is not unknown for some manufacturers quote maximum power at a higher than acceptable Total harmonic Distortion level (Usually < 1%) E.G. like 10%, making their equipment appear to be far more powerful than it actually is at audio levels where sound quality is not compromised.
Remember Peak Power (PMPO) figures are hugely exaggerated compared with the “RMS” values used by professionals. It also shows that there is little consistency in how much the figures are exaggerated making them almost totally meaningless.
Tags: Audio Power, RMS, RMS Power, Watts RMS Posted in: HiFi Jargon Buster
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