Sweetwater's power amp buying guide: matching amplifiers to speakers
Matching Amps to Speakers
B212XL Passive PA speaker
When you’re matching a power amp to a PA speaker setup, a good rule of thumb is to pick an amplifier that can deliver power equal to twice the speaker’s program rating. This means a speaker with a “nominal impedance” of 8 ohms and a program power rating of 350 watts will require an amplifier that can produce 700 watts into an 8-ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms. A quality professional loudspeaker can handle transient peaks above its power rating if they occur.
Using an amp with some extra “headroom” will help assure that only clean, undistorted power gets to your speakers. Headroom is the difference between the normal operating level of an amplifier, and the maximum level that the amp can pass without distorting. Music has wide variations in dynamic range; without enough headroom, you’ll find your gear clipping (distorting) far too frequently! Some professional amplifiers are designed so they have additional headroom. These amps can cleanly reproduce transient peaks that exceed their rated power. In this case select a model with an output power rating equal to the program power rating of the speaker. Consult the amplifier manufacturer or owner’s manual to learn more.
In some applications, such as critical listening in a studio environment, it is important to maintain peak transient capability. For these applications, use an amplifier that can deliver two- to four-times more power than the speaker’s program power rating.
If budget restraints or legacy equipment force you to use an amplifier with less power, extreme care should be taken to see that the amplifier is not driven into clipping. It may surprise you to learn that low power can result in damage to your speaker or system.