Howto info on Smith horn DSH

:o: I had this over on another thread that must be dead, so I've posted it under a new one
I've been going over the varous posts concerning the Smith horn, and I'm interested in building some. The problem I am coming up against, is getting enough info to design then build one properly.
I have down loaded the 1951 artcle from Audio Engeering written by Bob Smith, but it is not the best copy, on page 17 figure 5 there seems to be a triangler plug right at the mouth of the horn spaced 5/16" in front of the back plate. Can anyone enlighten me. also I'm not able to read the equations clearly.
Also is it possible for anyone who has design/construction info on these, Perhaps other magazine articules etc to be able and send them to me. I can take most formates including DWG DXF, JPG etc.:D

Thanks Dave C.