Root Mean Squared, or RMS, is a formula used to calculate an approximate average for the power an amplifier can continuously create and a speaker receives. When used in reference to speakers, the term helps identify the power of the speaker and the quality of sound you hear.
When you're designing a sound system, the RMS rating of the amplifier is a critical piece of information. The larger the RMS, the cleaner and louder the sound your amplifier produces. The amplifier powers the sound, the speakers receive this sound.
On a speaker, the RMS refers to how much power the speaker can accept from the amplifier. If your amplifier feeds too much power to your speaker, your speaker will first distort the sound, and then overheat.
When putting together a sound system, you need to balance the output of the amplifier and the input ability of the speaker. To do so, read the RMS information for the speaker. RMS presents an average of maximum power. A higher RMS means higher power from an amplifier, as -- on average -- the speaker can receive more power.
A further area of confusion is the ohm power of the speaker when referring to the RMS of the amplifier. In general, an amplifier provides a specific RMS to a specific ohm of speaker; for example 100 watts of RMS power into a 6-ohm speaker. When reviewing RMS, make sure your speakers are the same ohm as the speaker noted in the amplifier's information. If they don't match, the RMS information isn't accurate.
RMS is a relatively convoluted equation. It takes into account the power sent from the amplifier, the impedance of the current and the inductance of the magnetic field of speaker current and the current itself. It's difficult to measure yourself. As a result, use the standard measurement provided by the speaker manufacturer to help determine your speaker choice.