What Does RMS Stand for in Speakers?

When you read the specifications for audio speakers, you'll likely come across the term RMS, which stands for "Root Mean Square," a method for rating a speaker's ability to handle audio signal power. Although it is technical in nature, you don't need to understand the details completely to use RMS specifications effectively to compare different audio speakers.

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Average, Peak and RMS

Audio engineers measure power in terms of average, peak and RMS watts. Peak power is simply the highest reading obtained when measuring the playback of a typical song; it is the most power a speaker can handle in a loud burst of sound. By contrast, average power tells you what a speaker can manage for sustained periods. Mathematically, it is the alternating current voltage across a speaker's terminals times the current through the speaker, multiplied by the power factor, a number related to the speaker's efficiency. RMS power is the speaker current divided by 1.414, the square root of two. This gives a number somewhat smaller than the average and reflects a more accurate sustained power capability for a speaker.

Comparing Speakers

Because the peak power figure is the highest of the three ratings, speaker manufacturers may use it in advertising to make a speaker "look good." Average and RMS ratings, however, are lower numbers that give you a better idea of a speaker's capabilities. Always compare the RMS rating of one model against the RMS for another; never compare RMS versus peak, as they mean different things.

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