Amplifier Power Ratings

Power Lines

There is much confusion over amplifier power ratings.  There are two primary things to be aware of: what type of measurement a given rating represents and what this means as far as one’s listening experience.  The former is fairly objective while the later is very subjective.

Continuous RMS

This is the most rigorous of the power measurements, although even in this category there are a few “flavors”.  For example, what is “continuous”?  Ten seconds or ten years?  Also, is this at one frequency (e.g. 1kHz), the full audio bandwidth (e.g. 20Hz-20kHz), or the full bandwidth of the amplifier (e.g. 5Hz-100kHz)?

The next question is how appropriate this measurement is for an audio amplifier.  It is probably very appropriate for a precision programmable ac power supply, but I’m not sure how many people listen to continuous full-amplitude sine waves.  Some may feel better knowing their amplifier will be well within its limits with audio material, but as far as actual audio quality, there isn’t much benefit.

Burst Power

Like with continuous RMS there are a few ways of interpreting this measurement.  Is this the peak power of a continuous sine wave, in which case it is double the continuous RMS value, or does this represent the maximum instantaneous power, in which case it is a function of the power supply rail voltage at idle and the lowest allowable load impedance?

There is some merit to this sort of measurement, but the burst interval should be of a reasonable length.  A 20mS burst test is common with very high power amplifiers, such as those from Powersoft or Lab.Gruppen.  Measurement of actual program material indicates that a 200mS interval may be more appropriate – please refer to this AES paper.  Given a reasonable burst interval, this test is probably the most useful for amplifiers intended to reproduce audio material.  Please note that this burst power measurement may be given as either “peak” or “RMS”, with the former having twice the value of the latter.


This is a measurement of the saturated square wave power of the amplifier and is common with consumer and car audio products.  It tends to give an inflated power rating, which is no doubt why it is popular with low-quality audio products.

This test may be useful for giving a feel of what an amplifier is capable of when severely overdriven, but is not really appropriate for high-quality audio products.

One Response to “Amplifier Power Ratings”

  1. OT: power conversion | hilpers Says:

    […] of maximum square wave power and gives a vastly inflated rating over any sine wave measurement.…power-ratings/ And here: It appears to be average RMS output squared divided by […]