Why not horns?

One other thing that struck me is that despite being horn loaded, the Unicorn is still only 87 db or so efficient, according to the specs I found. A horn loaded speaker that is still that inefficient is certainly a unique beast as well.

I suspect that GP's Unicorn was an exercise in trying to make a full range single driver speaker system. As appealing as that concept might be, success in that quest has been allusive for all that have dared to try. The idea of a horn loaded omni directional driver would appear to be an oxymoron.

Yes horns and omni drivers are a unique combo for sure.

Most GP designs appear to limit the coverage of the DDD driver to the upper frequencies where Walsh drivers operate in a mostly wave bending manner, as I understand it. This is supplemented by more traditional dynamic drivers for the low end.

The Unicorn apparently trys to extend the range of the DDD lower where it like all Walshes I believe operate more pistonically in producing bass, but that does not appear to be the strength of the DDD. The horn loading and equalization applied in the Unicorn to the DDD bass region output appears to compensate for that.

Macrojack, my 4.5" drivers are only good to 70-75dB because I run them full range from 45-15,000hz. If they were cut at 300hz like your horns, they could be played over 100dB.

If you go with Folded transmission line or Standard transmission line they advertise that you can get the bass and volume levels.

I believe this Tang-Band W4-1337SD will give similar performance to your horns. I have used it in a cabinet as small as 8 1/2" high. You will loose some bass as compared to a larger cabinet but if you put them against the wall, you should be okay. I found the HF ttshhh ttshh, annoying and would require a low-pass filter to cut or reduce the HF. I also prefer the snappy, softer sound of paper to the crystalline clarity of titanium. But I also use bi-polar solid state amplification and CD's.

There are many good single drivers (so I am told). Especially the PHY and Supravox if you are willing to spend the money. Also Jordan JX-92S but I found them to be thin in the bass. Even with a large transmission line cabinet.

Hope this clarifies things for you.

Mapman, the DDD appears to be full range till it reaches well into the bass region. After that the DDD driver would need to be augmented with a woofer/sub-woofer for full range classification. Those lower frequencies have less apparent directional ques, and probably maintain the illusion of omni directional presentation well. Keeping the cross-over away from alternate drivers at higher frequencies where our ears are most sensitive and usually are have the narrowest directivity would seem to be preferable. Again the DDD doesn't have the mechanical cross-overs that the original Walsh driver had. Of course the catch is; they're pretty darn expensive.