What is wrong with negative feedback?

"Now of course you can imagine that one might do that with a more efficient speaker because it is possible, but really the limiting factor with the less efficient speakers was that the loudness cues made it uncomfortable to turn it up the volume any higher."

Hmm, I'm under the impression amp clipping generally becomes more of an issue at higher volumes with less efficient speakers?

I'm assuming that you run these with one of your tube amps, which would minimize loudness cues when distorting? All amps distort more at higher levels, correct? The question is in what way and to what extent the distortion is audible. For a given amp, this would occur sooner at lower volume with a less efficient speaker, all other factors aside, right?

Right. We were careful to not allow the amplifiers to clip during these tests. However it really did not matter which amp we used or in what combination. The higher efficiency of the speakers meant that amps were not working as hard and so were more relaxed.

That was 12 years ago. We've made good progress reducing distortion since then, so the amps have continued to get more relaxed.

06-25-10: Jamesgarvin
... "Seems to me the only way to make that determination is to take two identical amps, one with negative feedback and one without, and play them with the same source through the same speakers. I've not heard of anyone who has done that exercise, much less anyone who has heard it."

Hi Jamesgarvin;
Interesting. However, they could not be identical amps, even supposing that they only differed regarding feedback, but I assume you meant it ideally.
Practically speaking, we can, of course, choose one of each type from a number of respected designers and begin there.
When you referred to playing them with the same source, I'd like to reference "source" as recorded source.
Using acoustic instruments as an example:
If we are present in the recording space during the performance and we agree that the sonics are excellent, we'll have to verify that all components: mics, mic pre-amps, console or summing equipment, power-amps,
are non-feedback - as well, the same devices with feedback, We'd have to start there.
If this could be accomplished, we'd still have to consider
Class A, A/B, D, discrete/chips, SS/tube, etc.
We still haven't discussed what reference speaker system.
Considering all of the above, its amazing the amount of effort that drives the talented designers and enthusiastic lovers of audio and music.
For those concerned, having a very satisfying audio system is natural treasure.
I'm glad to see those efforts displayed here.