diyAudio Moderator Emeritus
Join Date: Jan 2003
Location: Near London. UK
Originally posted by metebalci
PS: What does True RMS DMM measure for a Vdc + Vac potential, I have seen different definitions for this?
The only definition of RMS is that it is the DC amplitude (current or voltage) that would give the same heating effect as the AC waveform. It is calculated by taking the Root of the Mean of the Squares. At RF, it is measured using a thermocouple to measure heating effect.
In most cases, you don't need a true-RMS DVM. The only time you need one is if you are concerned about heating effect and your waveform is distorted. We don't like distortion in audio, so a cheap and cheerful mean-sensing calibrated RMS of sine wave meter will do perfectly well. That is, any old £15 junk.
My true-RMS meter (I wanted a 0.025% accuracy meter, and true-RMS was included) can display the AC and DC components independently, which is occasionally useful.
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...