This is a French effort, from the website http://jipihorn.free.fr/, showing audio gear by Jerome and Thierry Prevost. I havn't had contact with them, but I assume they are brothers sharing a nice hobby. :)
They have several pages detailing this and other horn developments and show some of the design and construction steps. It's all in French so might be a problem for some, but the pictures alone are worth more than a million words.
(Note: although this horn consists of cells, due to its general lay-out and expansion style, it would probably be more accurately described as a radial horn. Examples of this style follow later.)