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Amplifier Power In Vs Power Out

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TheChair | 13:22 Sat 24th Apr 2021 | Electronics
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I've been looking at replacing my bass rig with a pedalboard preamp and a full range active PA speaker. What I find confusing though is that most of the speakers I've looked at seem to have a lower power consumption figure than their RMS rated output. For example, the LD systems ICOA 12 A has a rated output of 300W RMS, (1200W peak) but a power consumption of only 150W.

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This issue is the result of the standard used to test audio equipment – making it appear that an amplifier is giving out more power than is input.
Normal operation (representative of typical use) is considered to be where the amplifier output is loaded at 1/8th non-clipped full power. It is this loading that is used to define the input power.

So an amplifier having a 100W rms output may very well have an input rating of around 30W since it will have been tested with the output loaded at only 12.5W.

Many audio equipment manufactures make exaggerated power output claims for their equipment. The most reliable figure is the rms power output, but it is not uncommon to see unqualified power output figures that may be peak, music, rms etc power ratings – making it nigh on impossible to know the true power output.

See this wiki article for more info on the subject:-
https://en.wikipedia.org/wiki/Audio_power
Question Author
Thanks for your comment, Hymie, but it doesn't actually answer the question "how can any device output more power than is input".
It is as explained above.

I manufacture an amplifier with a genuine 100W rms power output.

For the purposes of the electrical input power rating, I test the amplifier with it driving a load at 12.5W rms (1/8th of its un-clipped output rating). Under these conditions of test the amplifier draws 30W – therefore I mark the product with an input rating of 30W (despite it being able to deliver an output of 100W).

Under operation at full power, the amplifier will be drawing an input power in excess of 100W (allowing for power losses within the amplifier) – but as explained, the 1/8th output power operation is used to define the amplifier input power rating.
Question Author
Thanks for clarifying that.
What a weird way of doing things!

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