Is anyone thinking about building Walsh drivers?

"I think that "stuffing a pillow" behind the driver as Ohm is presently doing is not the way to go."

I think this is the standard configuration provided to enable speakers to go closer to rear wall than full omnis otherwise and allow the speaks to fit into more peoples rooms like other speakers more easily.

That may be why they pass on the omni/walsh style tweeter. I'd like to see it though if possible in order for the dispersion characteristics to be similar top to bottom regardless of whether full omni or not.

I imagine cost management is a factor in the decision making process as well. The tweeter they use sounds very good. A "custom" Walsh style tweeter would likely add cost. Maybe a premium model of some sort with a separate Walsh tweeter might fly and still come in for a lot less than GErman Physiks, mbl, and their ilk.

But I also suspect that the niche high end market is not something OHM is really all that interested in, at least in the US, although they have started to market overseas in GErmany and elsewhere I suppose where their products can compete with the mbls of the world in a larger market for much less I guess.

OHM does do full omni versions for surround sound systems normally I believe where the sound absorbing materials inside the can are omitted.

I can see your point concerning close wall spacing. The omni's need a lot of room to breathe, and creating the correct acoustical environment is black magic a lot of folks would just as soon avoid.
As for the tweeters, they take a lot of skilled labor to build. It's not something you can pop out of an injection mold, and the key to profits these days seems to be not paying craftsmen or worse, farming it out to the Pacific Rim.
One of the ESL companies, I believe it is Acoustat, moved their production from the UK to China to contain costs. The Chinese company immediately started selling a knock-off with a different name for about 1/3 the UK price. The Chinese seem to be very challenged when it come to intellectual property

Mapman... You can mount a conventional cone driver backwards firing down, but it isn't at all like a Walsh driver.

The angle of the cone and its material must be such that sound propogated down the cone material is delayed by a time that, at every point down the cone, matches the delay resulting from the angle of the cone. (Sorry I can't explain that better). This is the key design feature which enables its superb phase coherency, as evidenced by accurate reproduction of a square wave.

Eldartford,

I'd say you are correct in terms of how a properly designed Walsh driver operates.

My understanding though is that Lincoln Walsh invented the principle, but never implemented a specific commercial design himself, though he was involved early on with the first early OHM products, something that no other makers of Walsh drivers can claim.

SO when I read that any conventional driver can be configured to operate as a Walsh driver (though most likely not a good one unless the principles of designing a Walsh driver are applied and realized properly somehow), I find it hard to argue. The quality of the resulting sound produced in the end based on applying the principles is what matters.

I read about people implementing their own "Walsh" type speakers using otherwise conventional drivers, but have never heard any, so I could not comment on the results achieved.

If it walks like a duck and quacks like a duck, it's probably a duck, but still not all ducks are created equal!

Eldartford is 100% correct. In the "A", the cone was two tiered and had two angles. The different angles reflected the propagation velocity of Titanium (upper), and Aluminum (lower). I think the "F' was the first in a series of compromises, in that all three cone materials were all at the same angle.
The theory behind the transmission line was detailed in a White Paper that Ohm would mail you for the asking back in the "70's. I have never been able to find it on the web, nor have I been able to get it from Ohm.
We did some experiments with two way "Walsh" speakers back then using off the shelf 10" CTS woofers and the foil tweeter that Infinity later bought.
It didn't sound too bad, and in fact a couple of musicians and wealthy audiophiles were impressed enough to consider backing a commercial venture.
Unfortunately, a profitable business model and art for the sake of art collided immediately and the project was doomed.
A lot of effort was put into dampening/stiffening the cone with things like roofing tar, and terminating the outer surround to coax transmission line behavior at the same time keeping a "back wave" from going back up the cone.
One big problem was that the roofing tar worked for a week or so, but then it started to really harden the the character of the sound began to degrade. After the business deal fell through, we never followed up.
We never did any serious tests, because we were a couple of broke kids playing with Hi-Fi and couldn't afford the gear to test with. They sounded good for a while, though