Axiom Home Page Forums General Discussion Technical Questions Buying an older receiver

Fred, dynamic power is a valid method of measuring amplifier output suggested by the IHF. It's measured by applying a tone burst for 20 milliseconds on and 480 milliseconds off every half second. The idea is that 20 milliseconds roughly corresponds to the length of a musical peak on a instrument, following which the sound level falls off. This tends to give a number about 20-30% higher than the continuous power rating which the FTC regulations require for amplifiers advertised in the U.S. The basic FTC requirement is at least two channels driven simultaneously at the full rated power for at least five minutes continuously.

You beat me to it. I bet that restriction is placed on the refurb units by the manufacturer.

I think I can do better used locally with a little patience.

Johnk,

Do you, in your vast arsenal of audio knowledge, have a chart anywhere that illustrates the dynamic range of instruments?

Vast arsenal indeed. I missed your reply while typing john.

I'll have to mull over what that means for a little while.

Thanks.

Basically it means that dynamic power is a secondary spec. To determine if an amp meets your application, look at continuously rated power.

...and ignored entirely when thinking about amp headroom?

I'd ignore it entirely, yes. Because I doubt that composers obey the 20msec/480msec duty cycle spec .

Now of course if you found two amps that had the same specs, price, etc but one had higher dynamic power, buy that one. That's what I mean by a secondary spec.

Mo, there's an interesting(and pricey)book on musical instruments which can be examined in part by clicking the preview button here . For example, scrolling down to p.31 shows a chart of some instrument dynamic levels.

Tex, you may want to research synthesizers as you would get pretty attack, sustain and release for each instruments. After you have the shape of the fundamental wave, the synthesizer will then add the harmonics and you will get a final waveform with peeks that can reach quite high, but for very, very brief periods.

"Dynamic range" can be used to many sauce and is sometimes used (quite often here in this forum) as the difference between the lowest sustain level and the highest one (the part our brains are actually registering as low/loud). It can also mean the difference between the highesr point in a waveform and 0db. The various definitions are all good, it's just a matter of using the one appropriate to your needs.

I am sure you can get simple synt programs on a PC to experiment.

You can also look at samples for Samplers as they may be more "real life" and easy to check with a wafeform viewer.

And I am sometimes wondering which sauce we are talking about.

Given that this stuff is defined and quantifiable one would think that it is well understood in the audiophile community, but it sometimes seems not.

I see head room numbers being quoted and they seem to contradict each other. For example to the folks at Crown, 6db headroom (from average) is nothing and is considered adequate only for compressed pop/rock music, yet I have seen it suggested here, by inference, that 6db amp headroom is just fine for all music.

I always think of headroom being the power available above the average C-weighted (thats the slow one isn't it?) spl measured when you are listening to a given piece of music.


Can you quantify that at all? How high, how long, and can we hear it? Crown allows for short term inaudable clipping in their power recommendations, but they don't explain what that means.

Hmm... a brief (1 hour) sidetrack to do some internet searches suggests that we can indeed hear it (at least in theory). In fact, the speed of the attack is one of the auditory cues we use to determine what instrument it is we are listening to.

I would love to hear more on this from you Eric. I suspect you have done a lot of reading on the subject.