What Size Amplifier Do I Need?

These are very common question we get:  What size amplifier do I need?  What amp will work with these speakers?  How many amplifiers do I need?

A good rule of thumb to start with is to pick a power amplifier that can deliver twice the power of the speaker’s continuous power rating.  For example, let’s look at Seismic Audio’s SA-155T (Dual 15″ Pro Audio PA/DJ Speaker Cabinets) which have a power rating of 700 watts RMS.  So, according to the rule of thumb, to power these speakers we would need an amplifier that can produce 1400 watts. Another important thing to take in consideration is impedance of the speaker. (The Ohms at which the speaker runs.)  Now, let’s go back to our SA-155T example.  The SA-155T have an impedance of 4 Ohms and, therefore, we would need an amplifier that can produce 1400 watts into a 4 Ohm load.  Using twice as much power as the speaker’s continuous power rating insures that you are getting a clear and undistorted sound to your speakers.

You don’t have to run 500 watts through a speaker just because it can handle that much.  If, for whatever reason, you have to use an amplifier with less power than your speaker, be sure to use caution.  If your amp is being driven into clipping, this could really damage your speakers.  Use your ears!  If you can hear that your speakers are distorting, crackling, or popping, you need to turn it down!  Just because your amplifier can put out 200 watts doesn’t mean you should run it at 200 watts.

For more information and help, be sure to visit Seismic Audio’s Tech Help Page.

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1 Response to “What Size Amplifier Do I Need?”


  1. 1 Jeff January 4, 2010 at 3:02 pm

    Great post. I always have just matched my continuous rating on the speaker with the continuous raiting that the amp can put out. I have always heard that underdriving a speaker though could do more wear and tare than just running it at its continuous rate. Not sure if that was always right but i figured id at least get a matching continuous or higher. Never would i get an amp that was 200w continuous for a speaker that was rated at 500w continuous. I figured if you matched the outputs and you saw clipping on the amp was to first back down and mark before the clip and then you know where your amp and your speaker are maxing out at. Does this even sound logical to anyone? haha


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