Stilljd...Even a "cheap" multimeter is plenty accurate enough. (An oscilloscope. if you had one would be the best because you could see the peak voltage directly). My RS meter is digital, and displays a new measurement about once per second. As the music volume varies you monitor the reading and take the highest one as the short term (1 second) rms value.From the rms value you can estimate what the peak would be. The meter is connected directly across the speaker terminals, at the amp or at the speakers. Not in series. That would be for a current measurement, but don't try that with a voltmeter.
You will be happy to see how little power is applied most of the time at moderate volume, but the increase during loud passages played loudly is surprising.
You will be happy to see how little power is applied most of the time at moderate volume, but the increase during loud passages played loudly is surprising.