Why not horns?

"Mapman, the original Walsh Drivers had 2 such mechanical cross-overs. I suspect that there was some cross-over in the lower than the extreme upper frequencies as well."

That is correct the original OHM Walsh drivers used three distinct sections for low, mid, and high end that resulted in two physical equivalents of a "crossover" between sections, though I would not equate these "physical crossovers" to electronic ones in regards to how they behave, particularly in regards to coherence.

"The DDD doesn't have any such mechanical cross-overs"

That is correct also, though an external electronic crossover and non walsh bass driver is used for full range in most GPs.

In the case of the OHM CLS, the Walsh driver, crossover, and tweeter are all considered part of the full range "CLS" driver.

In either GP or OHM case, for full range, with exception of the GP Unicorn, two drivers and a crossover are used.

Prez-
Here is an anonymous contribution sent to me by a horn enthusiast. I hope it provides some clarification.

----------------------------

I am not an expert on this but, when the sound forms in a pipe, and it leaves the end or "mouth, it becomes mainly a refraction wave. At the throat it is a pressure wave

Due to an 180 degree phase shift , there is an abrupt drop in pressure at the end of the tube, and the wave is reflected back down the horn, and the cycle repeats itself.

But, if the tube is made into a horn shape the pressure drop is not nearly as intense at the mouth, and the refraction wave is diminished so only a small portion of it reflects back down the horn. The throat of the horn is a High pressure wave.

-----------------------------------

More from the same source:

from.....http://www.physicsclassroom.com/class/sound/u11l3d.cfm

Refraction of Sound Waves

Refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. So if the medium (and its properties) are changed, the speed of the waves are changed. Thus, waves passing from one medium to another will undergo refraction.

One last point on the horn loaded Walsh driver used in the German Physiks Unicorn.

The increasingly pistonic operation of the DDD Walsh driver towards the lower end of the sound spectrum is what would produce the pressurization at the mouth needed to enable a horn to be used with a Walsh driver. The horn would not be exposed to sound pressure emitted orthogonally via wave bending in the Walsh driver, so I am pretty sure wave bending alone could not work with a traditional horn design.

Mapman, I won't argue the point of how the GP Unicorn works, but as long as the sound is emitting from a source, I suspect once could attach (a) horn(s) to it, if that's what they wanted to do. Though it would seem to be a contradiction of philosophies in this case.

Ok, enough beating a dead unicorn.

Ha Ha Ha! Dead unicorn, a horse with a horn, get it?