Speaker sensitivity vs SQ

Atma-Sphere that sound great but is way above my pay grade. But, I think you just explained why I like Pass and Curl amps so much?
Phusis, those are quite some speakers you have. What are you using for subs? They must be unusual to keep up with your main speakers.

@mijostyn  I don't know about Curl's designs so much, but Nelson does make fully differential amplifiers so he is able to take advantage of the lower distortion afforded, and yet have a nice 3rd to help mask the higher orders.

My opinion of speakers is very jaded now. I've been living with large ESLs for so long that most other speakers sound.....small, even if they go loud.
I find horn loaded designs very interesting but I have yet to hear one that I would consider. I have not heard Ralph's speakers, I'm sure they are excellent. I have heard a few at shows that were not impressive, but what ever is at a show. Some of the older Horn loaded speakers like Altecs and JBLs that I had a lot of experience with when I was young were all very colored. Back then K horns were the best but they did not image well and though not as colored as the other horn speakers you still knew you were listening to horns. Frankly, I liked the Cornwall better than the K horn.
I owned Heresy's for 10 years and for a teenage rocker with a Dynakit Stereo 70 they were great until I got Large Advents and a Phase Linear 700. The Advents were more natural and imaged very nicely. 
The Heresy's were the last and only horn speakers I ever owned. The problem is there are painfully few situations where you can hear them in a controlled situation. Some of them are very large, very expensive and few dealers are going to keep them on the floor. 
Those of us here have gone down our own path and become entrenched in one technology or another and always seem to think ours is best.
There is no single best. There are thousands of bests. Since we can't hear all of these systems it is fun to talk about them and hear about what other people are doing. In many instance you might learn something that you can apply to your own system.

@atmasphere wrote: 

"Harmonic orders above the 2nd decrease rather slowly as compared to a circuit that has a ’cubic non-linearity’ (produces the 3rd as the primary distortion component). An amplifier that has this quality has its distortion decreasing much faster as the order of the harmonic is increased! This is important since the ear uses higher ordered harmonics to sense sound pressure (and assigns the quality of harshness and brightness to them). IOW, an amplifier with a cubic non-linearity will sound more detailed (because distortion masks low level detail) and **smoother** because the higher ordered harmonics are at a lower level. 

"In terms of circuit design an amplifier with this characteristic must be fully differential and balanced from input to output. In this way even orders are cancelled with each stage in the amp (instead of being compounded), leaving the 3rd as the primary distortion component, at about 1/10th what you would get with a single-ended circuit, assuming that neither employs any feedback." 

VERY INTERESTING!! 

I think this explains part of the difference I hear between your amps and good single-ended triode amps, in particular:  

" An amplifier that has this quality has its distortion decreasing much faster as the order of the harmonic is increased!"  And, 

"...even orders are cancelled with each stage in the amp (instead of being compounded), leaving the 3rd as the primary distortion component, at about 1/10th what you would get with a single-ended circuit...". 

Thank you for putting this down in writing.  I copied it to a file so I can find it again.  

Duke 

Some of the older Horn loaded speakers like Altecs and JBLs that I had a lot of experience with when I was young were all very colored. Back then K horns were the best but they did not image well and though not as colored as the other horn speakers you still knew you were listening to horns.

Like any other tech, horns have benefited dramatically from the aid of computer optimization. I owned Altecs, Klipsh and EV horn systems and there's no way I would go back to them; as you say they were very colored (and lacked bandwidth, particularly in the bass). The Classic Audio stuff is a different beast altogether- neutrality is a good descriptor. The speakers produced by Audiokinesis using waveguides had a similar neutrality- you found yourself involved with the music rather than the speakers.