[Vintage-Audio] Re IHF Vs RMS

Tue Oct 28 18:05:02 2003

IHF ratings were a very good "selling" tool to use at the consumer level.
Pete

On Tue, 28 Oct 2003 12:56:55 -0500 "Duane Fischer, W8DBF"
<[email protected]> writes:
> Ed,         
> 
>         
> With all due respect, I disagree with Bob's interpretation of the 
> IHF rating
> system. It was far more accurate than the peak power used by most 
> manufacturers
> at the time of its introduction. I think that Roy is correct, as is 
> Ed.         
>         
> I have remained active in audio for almost four decades and am 
> reasonably aware
> of the changes as time went along.         
>         
> The consumer in the sixties, primarily audio buffs, knew what he/she 
> was buying
> and/or building. They were not misled by the peak power numbers. 
> Today the
> consumer market has no clue and is influenced heavily by inflated 
> and/or
> deceptive numbers of power delivery. While these numbers are 
> probably true, so
> as to avoid false advertising litigation, unless the buyer 
> understands some
> level of electronics he/she will not know the difference. More power 
> is better! 
> 
>         
> DBF        
>   
> 
> ----------
> From: Ed Shafer <[email protected]>
> To: [email protected]
> Subject: Re: [Vintage-Audio] Re IHF Vs RMS
> Date: Tuesday, October 28, 2003 9:45 AM
> 
> Bob,
> 
> I remember that bogus power rating too, but I believe it was called 
> IPP
> (Instantaneous Peak Power). Something like twice the RMS rating, and 
> if it was
> stereo, they doubled that. Just to jack up the numbers. Heck, they 
> may still be
> doing that - I haven't bought a (new) stereo in years.
> 
> Ed Shafer
> 
> --- "Robert    J. McKee" <[email protected]> wrote:
> > 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 <[email protected]>
> > > To: <[email protected]>
> > > 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

________________________________________________________________
The best thing to hit the internet in years - Juno SpeedBand!
Surf the web up to FIVE TIMES FASTER!
Only $14.95/ month - visit www.juno.com to sign up today!