How to calculate amplifier requirements

Calculating the number of amplifiers needed for a particular speaker setup is easy, provided you know the specifications of the speakers. Typically speakers are rated in continuous, program, and peak. The rule of thumb is 20% over the program rating. Simply take the program rating and multiply by 1.2. Keep in mind to match the resistance rating (such as 8 or 4 ohm).

Why 20% over the program? Well, it has to do with the load created by the typical music passage. A continuous rating is determined by a white or pink noise signal which is constant energy across the entire bandwith, and most music is not like this. At the other end, peak signal is the momentary peak signal ability. So, to provide power over the program means the amp and speaker have a comfortable amount of headroom and can operate within spec.

Of extreme importance, is to not underpower the speakers. Underpowering speakers is the worst thing you can do, and that will most likely cause your speakers to melt. Why? What will happen, is that you will drive your amplifier over the maximum power output which will cause the output signal to distort. This distortion will have a clipped waveform, and lots of clipping will look like a square wave to the speaker. Unfortunately, enough power will turn that square wave into a DC pulse, and DC current is what literally melts the wires in the driver. So please, never, ever underpower your speakers!

Hope this helps, and for related topics, click on the following links: Understanding PA systems, Designing Front of House systems, Calculating Resistance in Parallel, or Ask us a Question!