I didn't see anyone disagreeing with that. But it is a discussion of low impedance at low volume and we're laying out the reasons and factors involved with such a question. And I find the science that someone like Wyn Palmer can add to be very interesting. That's also the reason things tend to get off topic and go to related issues.
What did you monitor and what results did you get?
MC240 vs MC7270 ... no difference whatsoever in dynamics at low levels ... zero ...
That's what I would expect. And has already been explained from multiple perspectives and variables as to why that would be.
What was the criteria of the test? Was it strictly listening, monitored distortion, etc? Were the speakers the same model with different coils or was it dummy loads? I agree with you, but I'm thinking your test may be lacking in supporting data.
Speakers were B&W DM 580
It doesn't really tell me how you tested anything other than you set multiple amps to the same level. If you used only 1 set of speakers, how do you compare impedance? How did you determine the sonic quality? I'm assuming by ear. I'm not trying to pick on you, just trying to fully understand the test.
Myself, my buddy Mike, and my wife all took turns listening. Listener had the A/B switch in hand and could switch anytime they wanted to. Not one of us could tell any of the amps apart - at all, under any circumstances.
I already said I believe you, but I thought some details would be helpful. I was wondering so I could use any information in the future if I was to build or buy an amp, I could make a more informed decision on what's best. It was confusing because you came on here kind of implying we're morons for talking about the engineering aspect of amps and said it could be done scientifically. Then only mentioned an A/B switch. Which at first I thought it was referring to class AB. You could have just said set two amps to the same level and toggle between while listening. Not really that scientific, but is valid none the less.
Slew rate distortion occurs when some part of the amplifier is asked to change voltage at a rate which is greater than its ability to do so and hence it enters a non-linear region. To avoid that without changing the design of the amplifier one of two things can occur besides the trivial case of keeping the level low enough using the volume control- either the input signal is deliberately band limited using a built in low pass filter to avoid any possibility of the signal exceeding the rate - which would be a good idea with say, synthesized music, OR the input power spectrum is such that the rate of change is naturally limited- i.e. that the input signals are pink noise-like (1/f) with a built in upper bound, which is most like natural music, or red noise-like (rap music (a joke!)). Interestingly enough some sources (such as some MC cartridges for example) with substantial peaking either in the high sonic or supersonic regions can induce distortion as a result of their changing the 1/f characteristic of music at HF.
It absolutely does not have to be that way, at least not at audio frequencies. It's harder to produce an amp which has extremely wide bandwidth (necessary for small risetimes) with no slew rate limiting as the output voltage increases, but not impossible. But, it certainly can be argued, beyond the point where the amp remains non-slew rate limited at all times both internally and externally, there is no purpose in having a smaller rise time and indeed there are negative aspects of such a design.Hmmm...the suggestion I heard was that the smaller amplifier has the rise-time advantage - even when both amplifiers are driven to identical voltages.
Again, I cannot comment on how true this is, or even if.
I understand how slew rate limiting limits frequencies above its capability. But it doesn't explain what you said about how having a HF and LF helps slew or saves tweeters. If you have an amp with a 100 volt max and you have a 40v HF on top of a 50v LF so that it is not clipping, and the HF is below the frequency the slew rate can produce, how is that different or easier on slew rate than if the 40v HF was produced on its own without the LF? Doesn't the amp have to keep up with the same rate of change whether it starts at zero or if it starts at 50v? The slew still has to be as fast for either scenario and wouldn't reduce the HF amplitude because it was used at the same time as a LF.
Actually the 40v HF on its own is more benign than the 40v HF plus the 50v LF as the max rate of change will be equal to the sum of the max rates of change of both components (assuming they are not related in some way that prevents the maximum rates of change occurring simultaneously and in phase).
OK got it, we're on the same page now.