[Vintage-Audio] Re IHF Vs RMS

[Roy Morgan]

At 04:41 PM 10/26/03 -0500, you wrote:

>
>Greetings,
>
>What is the difference between the IHF (Institute of High Fidelity) and RMS
>power rating systems?  Which is the more accurate and why?

Duane,

The IHF measurement is an RMS method.  The "accuracy" of measuring power is 
based on a number of sources of error, including the error of the resistor, 
the error of the true RMS voltmeter and other factors.  There is a lot of 
argument about whether this or that or some other method of measuring 
amplifier output is better than another method.

At this web site I find the following explanation of the IHF method, which 
is based on a measurement of RMS voltage.

The web site:
http://www.hifi-writer.com/he/misc/rmspower.htm

I quote:
'... measured according to IHF A202. That is, using the correct test signal 
(a sine wave), the correct period of time for measurement (more than five 
minutes), a properly calibrated, true RMS-reading voltmeter with an 
accuracy of better than 1% of reading, without exceeding a specific level 
of distortion (0.1%) into a defined load (usually 8-ohms) with the 
amplifier first having been pre-conditioned by means of driving all 
channels simultaneously with a 1kHz sinusoidal signal to a nominal power 
output into the rated load equal to 33% of the rated power output for at 
least hour (or more if protective circuitry interfered with continuous 
operation). "

Roy