OK, I promised a power test in another thread, here it is. It's easy to do, all you need is an AC voltmeter with a low voltage scale. Anything in the 5-20V range should do. If your meter has only high voltage AC scales (200V-1000V) it won't be accurate enough for this.
How to proceed:
  1. Download this 120Hz file. Test Signals
  2. Unzip it and burn it to a CD or put it in whatever digital playback gadget you use.
  3. Select and play back a few music tracks as loud as you ever do (like after a few beers.) Take note of your volume settings - you probably know where they will be already.
  4. Use the highest setting you found when playing back music really loud. Leave the volume control there for the following measurement.
  5. Playback the test tone and measure the voltage at your speaker terminals. Measure at the amp or at the speaker, either is fine.
  6. Make a note of this voltage
  7. Take the square of the voltage* you measured from the test tone (multiply it by itself). You now have the minimum power rating of amp you need. Easy!

The file is a mono 120Hz sine wave in MP3 format. The MP3 is inside a zip file. Just unzip it and burn it to a CD or put it on whatever digital playback device you use.

Lets take an example:
  • You play a few tunes nice and loud.
  • You find the highest setting of the volume knob during your loud playback.
  • You play the 120Hz tone at that volume setting and measure 3.5 volts AC at the speaker terminals.
  • 3.5 squared is 12.25 (3.5x3.5=12.25)
  • You need an amp that can supply at least 12.25 watts RMS into your speakers. With that much, the amp won't clip, even on your loudest music.


You may be surprised how low the power is. In fact, that's the rating in RMS watts of an amp that will allow you to play your loudest music and not clip. Normally, you probably use a fraction of this power. My max is about 6W with my A5s, in my small room.

If you have questions about this test, please don't hesitate to ask, I'll do my best to explain. The 120Hz and -12dB point were chosen for several reasons, one being to make the math easy.

*assuming an 8 ohm load.