What does one purchase after owning horns?

Shadorne, Klipsch uses the "non aggressive" horn type you mention. However, because of the horn type AG uses, I find the seated distance between them and the listener needs to be greater,ime. However I have "heard" this rule be broken in many cases. I have heard many Lascalas (and Khorns for that matter)in which the owners have changed out the mid horn(to Altecs mostly)and I have not liked it as much as the original. I felt it threw the balance and coherence off. Other things as well. All of these horn designs were available to PWK, but I think he made excellent choices for his models. I know it is a matter of personal taste.

T_bone, In the case of Avantgardes, all you have to do is look at what sort of amplifier the designer is using (that is the case with most speakers). He uses a low power transistor amplifier, which explains the 'crossover' of the Trio (its all caps- no chokes, so the impedance of the speaker drops as frequency increases since the lower frequency drivers are not rolled out of the circuit).

It is for this reason that despite the efficiency of the speaker, quite often larger tubes amps are preferred, so they won't sound rolled off. Our Croatian dealer sold a number of MA-1s to Avantgarde Trio owners for this reason- you don't need 140 watts with that speaker! IME the smaller Avantgardes are less problematic in this regard.

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With regards to distortion in horns, to be kept low the design of the horn is quite critical. FWIW, the guy that did the JBL horns also designed the horns and drivers for TAD. The TAD horn has a problem with spiky response right near the cutoff frequency on their driver. Classic Audio Loudspeakers ran into this problem and had a new horn designed by Bruce Edgar that does not have any issue with this at all.

IMO the fact that horn-loaded drivers don't have to move much to make a lot of sound helps keep their distortion down. If set up right they can be as low or lower distortion than anything out there. If set up wrong the distortion can skyrocket. As in all fields, the application of generalizations is fraught with difficulties!

Klipsch uses non-aggressive horns? Huh? Only the humble Forte uses a tractrix flare. IME (I have owned K-horns and LaScala) these speakers have far more audible horn coloration than the AGs.

Conical mid horns with proper (thick, non-resonant) construction and the bit of necessary EQ have virtually no horn coloration - none.

But there's still a substantial downside - no mid horn can go lower than a couple hundred cycles at the very best and so you are always going to have an xover in a pretty critical region. Not that it can't be made perhaps close to inaudible, or at least non-objectionable. But this and other trade-offs will always remain.

" As in all fields, the application of generalizations is fraught with difficulties!"

Amen, brother!

"IMO the fact that horn-loaded drivers don't have to move much to make a lot of sound helps keep their distortion down."

Mass and inertia are certainly big considerations when designing any high performance speaker, no doubt.

The bending wave theory of sound propagation associated with Walsh style drivers is another design approach that I think solves much of the problem in a very unique and innovative manner.

Of course the radiation pattern of a Walsh driver is at the exact opposite end of the spectrum from horns or waveguides.

Its cool that there are so many different ways to tackle the same problem!