Originally Posted by DonH50
It takes an oscilloscope or special detector to measure instantaneous peaks.
My tool of choice is a mutichannel pro grade audio interface running at 24/96.
Matching up with a AVR output takes a calibrated attenuator that can take the ca. 40-100 volt signals from the power amps down to the 1-6 volts that audio interfaces swing with.
A voltmeter won't do it, at least most won't (you need one with wide bandwidth and a peak hold feature; there are some but they are not your average Radio Shack or other bargain meter).
IME the capture time of even Flukes is far from instantaneous. True RMS is desirable, but it also tends to slow peak response down.
No, most analog voltmeters are not the tool of choice. Oscilloscopes are better but you need some kind of recording or holding facility because transients are not forever. A 12 bit USB oscilloscope adaptor for a PC seems like a good tool and they are not prohibitively expensive any more.
And, there is the problem of converting volts into acoustical output; there's no easy way to confirm XX volts is actually outputting YY dB SPL due to the (in general) unknown transfer function from terminals to sound (acoustic output). Apples and oranges.
If you want to make accurate measurements of SPL you will have a mic calibrator, and once you have one of those relating volts to SPL is actually pretty easy.
Max to me is max, be it instantaneous or longer in duration. If you want to say "maximum average value" then add headroom to a peak value I understand what that means. Specs such as THX determine a max (peak, whatever) value above a defined reference level and so headroom is already taken into account. I doubt folk listen at 105 dB and then want another 10 dB of headroom (I am sure there are some). At some point the argument becomes academic. Well, until you blow something up... I typically listen around 70'ish dB and the system can output 105 dB max peaks. Enough for me.
To put things into perspective, the max SPL for professional gear is often spec'd at 116 dB.