Choosing the Appropriate Amplifier for Speakers and Subwoofers

When choosing an amplifier to drive speakers or a subwoofer, the RMS per channel of the amplifier should not be exceeded by the RMS of the speakers. If the speaker RMS exceeds the amplifier's RMS per channel, they will not receive enough power to perform at their best sound quality. The amplifier's RMS per channel can exceed the total RMS of the speakers being connected, but care must be taken when adjusting the level (or "gain") on the amplifier so as not to drive too much power to the speaker. Exceeding a speaker's RMS will cause it to be louder, but sound quality will be reduced. Frequently exceeding a speaker's RMS by large amounts, or exceeding the peak power rating, can damage the speaker.

RMS (or root mean square) is the amount of power (expressed in watts) a speaker should receive to perform at its best audio quality, and will cause no damage to the speaker. Peak or maximum power rating is the most power (expressed in watts) a speaker can receive without causing damage.

As an example, the Apollo 4 channel marine amplifier has an RMS of 150 watts per channel. The Signature Series 3 6.5" speakers have an RMS of 75 watts per speaker. One pair of these speakers RMS adds up to 150 watts, and so connecting a pair to one channel on the amplifier with a 4 ohm resistance (standard configuration) will match the RMS perfectly. The same amplifier, if speakers are connected with a 2 ohm resistance (in parallel), has an RMS of 290 watts per channel. The Signature Series 3 8.8" speakers have an RMS of 130 watts per speaker. One pair of these speakers RMS adds up to 260 watts, and so the same amplifier is more than capable of reaching their RMS. However the channel is still able to send more power to the speakers and so care must be taken not to too greatly exceed their RMS.