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In Reply to: RE: Frequency Response posted by Ian L on November 13, 2022 at 15:43:22
Well, no wonder the graphs look like that. The output Z of the SET is no match for the vagaries of a LCR load. And although I realize a resistive load won't produce the same curve as a real-world speaker, it's the only standard we have. The last thing I want is to have data presented on the basis of someone else's idea of the effect a loudspeaker will have. Totally ridiculous, and no idea why they would have thought this was appropriate for readers who only want to judge the amplifier's performance.
Follow Ups:
While my first impulse is to agree I also have to admit that I don't know much about it. Maybe there's a standard industry thing . . . . . like using a model that represents an EBP of 75 ? or something like that.
On the other hand, Mr. Atkinson is himself a , I don't know, what would you call it. . . . his own thing. (?) Everybody has heard of him. He can go ahead and design any test he wants. I see where it makes sense to do the test in a way that represents how well the amp drives a complex load. The trouble for us is there's no path to knowing exactly what he did and why, other than a lot of Google searching. One could email him I suppose.
I only looked at that article because I was searching to help dbKhorns find info that would define the needed power transformer. In general those magazines don't interest me much as they are only for people looking to buy, not to build. Better info here and other forums from peeps like PJ et al. : )
Atkinson discussed the simulated speaker load in some detail in a Stereophile article "Real Life Measurements" dated Aug, 1995. Atkinson discusses the desirability and need for such a standardized load and that their design was developed with assistance of Ken Kantor of NHT at the time. The circuit schematic is presented along with a brief explanation of the function of major components. The SP circuit is significantly different from the one at the "hack" link. Interestingly, simulated speaker loads were hot amp testing discussion topics back then and there were competing designs. One notable one was from Arnie Krueger (ABX). Similar to SP's load but different in the details.
I find the data produced by SP's sim speaker load both interesting and useful. I don't believe it's intended to differentiate betw amplifier goodness and badness but more to point out that sound will be more or less dependent on the speaker impedance curve. So choose with care vs choose with abandon.
When SETs first hit the American scene some 25 years ago, the conventional wisdom was deeply disturbed. It had long been accepted that the best amps had flat response, zero distortion, and zero output impedance. An early reaction was to "explain" their attraction by pointing to the change in frequency response. As I recall, the stated motivation for a speaker impedance model was to show that effect.
I suspect there was also an unacknowledged motive to show how awful the frequency response and distortion was, and push back on what seemed a ridiculous fad.
That's rather insightful, Paul: "an unacknowledged motive to show how awful the frequency response and distortion was..." LOL, you're probably right, especially considering even the best tube amps were being dismissed by the solid-state mainstream.
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