How much power do you really need? A lot. But all car audio components come with their own power handling specifications, and you should start there when determining how much power you’ll need.
On amps, for instance, you’ll see two types of power specs: Continuous, and Peak (or Max) power output. The continuous power output rating is determined using a constant test tone. The peak power output rating describes how much power the amp produces in short bursts. This is more comparable to the nature of music, which tends to go up and down, in intensity, a lot.
For a speaker rated at 100 watts peak, you should get a 100 watts/per channel amplifier to safely get the greatest amount of volume from that speaker. If all you know is the continuous power of a speaker, use "The 3/4 rule": divide the continuous rating by .75 to calculate the maximum amplifier size. (For example, a speaker with a 50 watt continuous rating can be safely used with an amplifier of 70 watts/channel [50·.75 = 66.7, round up to 70 watts]).
For most systems, 30 to 50 Watts (per channel) should be fine for primary speakers. Apply more (two to three times more, or 100-150 Watts) to your subwoofers. If you’re powering your tweeters independently, they can get away with less power (20 - 40 Watts).
A caveat: Speakers can be harmed when you push an amp beyond its power capabilities. It’ll “clip” the signal, which produces both mechanical and thermal stresses on a speaker's voice coil. The speaker's voice coil gets banged around, overheats, and ultimately breaks. But you’re actually less likely to blow a speaker by using too much power than you are by using too little power. If you like to play it loud, get a bigger amplifier.
This article was last modified May 25, 2013