[Vintage-Audio] Re IHF Vs RMS

[Robert J. McKee]

The so-called IHF power measurement is BS from the low-mid
fi manufacturers to inflate the published numbers... the sucker
ball for the unknowing.  It is generally in the neighborhood of
twice the RMS watts unless Peak power which may be four
(or more?) times the real capability of the power source.  And
do not forget the distortion factor in the numbers.

A complex music waveform has nothing to do with a pure
sine wave so we are really talking just a defacto way of
comparing one amplifier to another.  So for a realistic
comparison I'd prefer to look at RMS watts and the
dynamic headroom of the amplifiers being compared.
The final judgement of course will be listening.

Bob McKee



> [Original Message]
> From: Roy Morgan <goodguy3@amdiac.net>
> To: <vintage-audio@mailman.qth.net>
> Date: 10/27/03 5:40:01 PM
> Subject: Re: [Vintage-Audio] Re IHF Vs RMS
>
> 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
>
>
> _______________________________________________
> Home: http://mailman.qth.net/mailman/listinfo/vintage-audio
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer@usol.com **