A couple of interesting tidbits:
It's RMS power
It's at a minimum for only the main L and R channels
It's at 1% THD+N to accomadate tube amps that can't hit the original proposed 0.1% limit
It doesn't say anything about the the rest of the channels of a multi channel amp
It's gotta be at least 77 degrees, so you can't test an amp at low temps, when it couldn't put out the power at higher temps
They received lots of informal comments, but only a dozen or less "formal responses" to the proposed changes over the last 4 yrs they have been considering it
It’s not RMS:??? There's no such thing as "RMS power", how'd they mess that up?
Edited to say "contnuous".??? There's no such thing as "RMS power", how'd they mess that up?
Edited to say "continuous".It’s not RMS:
Any power level from 250 mW to the rated power shall be obtainable at all frequencies within the rated power band of 20 Hz to 20 kHz without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input. Provided, however, that for amplifiers utilized as a component in a self-powered subwoofer in a self-powered subwoofer-satellite speaker system that employs two or more amplifiers dedicated to different portions of the audio frequency spectrum, any power level from 250 mW to the rated power shall be obtainable at all frequencies within the subwoofer amplifier's intended operating bandwidth without exceeding 1.0% of total harmonic distortion plus noise (THD+N) at an impedance of 8 ohms after input signals at said frequencies have been continuously applied at full rated power for not less than five (5) minutes at the amplifier's auxiliary input, or if not provided, at the phono input.
* * * * *
(g) Rated power shall be minimum sine wave continuous average power output, in watts, per channel (if the equipment is designed to amplify two or more channels simultaneously), measured with all associated channels fully driven to rated per channel power.
(h) Associated channels for multichannel amplifiers shall include, at a minimum, the left front and right front channels used for reproducing stereo programming. Provided, however, when measuring the maximum per channel output of self-powered combination speaker systems that employ two or more amplifiers dedicated to different portions of the audio frequency spectrum, such as those incorporated into combination subwoofer-satellite speaker systems, only those channels dedicated to the same audio frequency spectrum should be considered associated channels.
Thanks!Edited to say "contnuous".
This is actually very useful...thanks. I've been an audiophile for 50 yrs or so. In my mind, RMS is the same as continuous, but I know understand the diff.Thanks!
For others following who might not know why the nitpicking, it is a definitions and unit thing. Typically current and voltage are expressed as RMS (root-mean-square) values, which is the square root of the mean (average) squared. You calculate the average of the squared values, then take the square root of that number.
For discrete signals, you square each data point, add them all, divide by the number of points, and take the square root:
Vrms = sqrt[(v1^2 + v2^2 + ... + vN^2)/N] where v1...vN are the N samples you are using
For continuous signals you do an integral (copy and paste from Wikipedia) for defined interval T1 to T2 (first integral) or over all time (second integral):
View attachment 385488View attachment 385489where f is voltage (V) or current (I).
Math aside, the importance of RMS values is that they allow us to compare varying voltage and current in a standard way, and the RMS value is equivalent to a DC (constant, battery) signal of the same amplitude. For a sine wave, the RMS value is peak voltage divided by the square root of 2: Vrms(sine) = Vpk/sqrt(2). That means a sine wave that is 2 V peak-to-peak (2 Vpp), which is 1 Vpk (peak), is 0.707 Vrms and is the same as a DC (battery) of 0.707 V. There are similar equations for many standard waveforms, and for more complex waveforms we can either calculate the integral or sample the signal and perform the discrete calculation using a computer (or analog measuring device).
Average power is the product of RMS voltage and RMS current: Pavg = Vrms * Irms and that is how amplifiers are rated. You can see that the units do not work out to provide "rms power" -- it would be rms * rms = rms^2, which does not make sense as far as units are concerned. There are more subtle reasons why a unit of "rms^2" is not useful, but just following the units is enough to tell us why there is no "rms power" or "Wrms".
Root mean square - Wikipedia
en.wikipedia.org
NP. For me, RMS refers to voltage (in V) and current (in A), and their product is average power (in W). I compare continuous to peak power, a time-based metric, so continuous average power is the long-term power rating.This is actually very useful...thanks. I've been an audiophile for 50 yrs or so. In my mind, RMS is the same as continuous, but I know understand the diff.