is there a way to test the RMS output of an amplifier?? (1 Viewer)

[Manuel Delaflor]

Im planning to make a CD with test tones, then knowing the sensibility of a speaker to an specific test tone, like 1Khz @ one meter, and the RMS output of an amplifier take some tests with an SPL meter.
Then extrapolate the results to test another amplifiers. How do this sound? is it plausible?
------------------

 

[ThomasW]

http://www.eatel.net/~amptech/elecdisc/measpwr.htm
This will give you a good idea as to what's involved. Obviously you can ignore the instructions related to the power supply of the car amp
And yes you do need a "True RMS" Digital Multimeter.
And no you can't use this info for any other amp than the amp that is actually has been measured

 

[Jack Lee]

For power, you need to know the voltage and current (or a supplied resistance curve which is inferred originally from voltage vs current and current vs current measurements).
For a useful power limit, you need to know where the onset of clipping begins. Either a max. voltage or maximum current rail will be approached for a given frequency and speaker resistance, leading to a gradual flattening of the crest of the sinewave. That's more or less meant by a 100W ampflier, it starts to clip over 100W.
Working back from the sensitivity of a speaker is a round about way. Usually sensitivities are given over the full range, not at a specific frequency. On top of that, it does not tell you when the amplifier is clipping. At best, you know at which volume setting the amplifier is produce a rms voltage of 2.83 volts (1watt into 8 ohms).
To measure clipping, you can make a visual check by observing the voltage/current on a scope or use somekind of spectral analysis package w/THD measurements.
If you measure the current, a non-invasive tool like an amp clamp or Hall probe will spare you the risk of burning out the scope.
You can use a high power variable resistor as the load and measure the voltages on a scope or anaylyzer.
IF you use a speaker as a load (i.e you want to measure THD w/a microphone), beware of how loud that maybe and damaging the drivers.
Darn Thomas. You posted while I was writing my post!
Same basic idea...
[Edited last by Jack Lee on August 27, 2001 at 08:49 PM]

 

[Manuel Delaflor]

Thanks to both. Sadly, Im thinking in a way to use only what I got right now, not scopes or dedicated equipment. I don't know electronics, so I just want to know if it is plausible to make "common sense" tests using and SPL meter and two known references to extrapolate results for another amplifier...
------------------