How come Horn + woofer designs are not more popular?

That is why Howard Johnson made 28 flavors. But, too bad we could not hear each other's systems.

Phusis, all that is nice but relative to what? We are not trying to blow up the Empire State Building. If you like pea watt amplifiers then you need all the efficiency you can get but in real life you can get all the volume and dynamics you need with dynamic drivers and good powerful amps. I am a linear array ESL fan and I guarantee you will never get as realistic a presentation out of a horn system all that rubbish aside.

Mike 

Wow, that should scare the hell out of your wife.

I'm not being facetious guys. I am trying to learn here. Way back I had Heresys and I loved them. In 1970 we did not have much for power. With a Dynaco Stereo 120 these things would rock. No deep bass but then nobody knew about sub woofers. They were three way. So let's assume we are using a 12" woofer infinite baffle and cross at 1000 Hz to a horn, what does it take to make a horn go from 1 to 20K with reasonably even dispersion and not sound like a goose honking. Duke's Speaker has multiple other drivers including three tweeters firing out back along with whatever is in the LCS box. It is anything but a two way hybrid horn speaker which to me means one horn and one woofer. I have never heard Duke's speaker and I am making absolutely no comment on their performance. So please Audiokinesis if there is a way to do this I would love to know. Like I said before my knowledge of horn technology is limited. Hear from you when you get back. 
Another issue that bothers me a little is the assumption that horns are more dynamic than other speakers. Horns are more efficient than most other speakers for sure but any speaker can be just as dynamic given enough power and power handling capacity. Horn speakers may have an absolute higher volume level at a given distance but very few of us listen at those levels. Our ears do have a pain threshold. In the end horn speakers are point source radiators and I personally do not think they present the music in as realistic a fashion as an ESL or Planar linear array. Maybe someone will build a horn version of Bob Carver's Ultimate line source. Think what that would look like:)

Audiokinesis, I would like you to tell me how you would make a two way hybrid horn speaker.
Otherwise I could not agree more. The business about woofer "speed" is unfounded. The only issue with the larger woofers is pistonic control thus the use of stiffer pleated surrounds. The free air resonance of these drivers actually tends to be higher in spite of their size. Theoretically with a larger woofer the distortion should be lower as it is more likely to be operating in it's suspension's linear zone.
I do think the directivity of horns is an advantage. But I think you minimize primary reflections from the floor and ceiling. I am not learned in horn design at all but I believe you can make a horn more directional vertically than horizontally which would improve things. The reason I am so fond of dipole vertical arrays is that you only have one primary reflection to worry about, the one behind the speaker which is easy to deal with aside from the way they project power. As you say late reflections are not a problem as long as your listening position is well into the room. Having your seat right up against the rear wall is....not a good idea. Then there is the issue of room size. Small rooms are never going to sound as good as large rooms. All the late reflections come too early confusing the sound stage.
IMHO rooms smaller than 15 X 25 should not be used for an ultimate system. You can scale a system down to a 10 X 18 room but that is not going to be ideal as the sound stage is going to have a less than realistic size. 

Oh, back on topic, there is a compromise in a two way horn system that is difficult to get around. You either have to run a woofer up into the midrange or make a very large horn to get down to where most woofers do well. I do not think there is a satisfactory middle ground. Look how large a K Horn midrange horn has to be just to get down to 500 Hz were it crosses to a 15 inch woofer. This is one area were that ESLs have a major advantage over both horns and dynamic speakers. You can easily design a speaker that is One Way all the way down to 100 Hz as long as you can live with the size. 

Good speakers play everything well and make bad recordings sound better even if they are not as good as the best recordings. There are good examples of every type of speaker (except the Hill Plasmatronic.) Mostly what you like depends on what you were exposed too. If you have only heard crappy horn speakers that is the opinion you will have, same for ESLs. Most people have dynamic speakers because they are easier to build, can be more aesthetically pleasing and are generally smaller than the best examples of horns or ESLs. My problem with most speakers is that they are hard to integrate into a normal size room acoustically. The room and speaker are a system. Some speakers will never sound good and some rooms will never sound good. Thinking about my self I go with what I have learned to work with and know I can get to work to my expectation in my own room. Making mistakes gets far too expensive at this level and I have already made enough of them.