I used to work on the calculation of 3 different horns

1) quasi elliptical
http://www.diyaudio.com/forums/attachment.php?s=&postid=1532641&stamp=121275
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2) Iwata_Le_Cleach:
http://www.diyaudio.com/forums/attachment.php?s=&postid=1532652&stamp=121276
0839

3) Controlled horizontal directivity
http://www.diyaudio.com/forums/attachment.php?s=&postid=1532660&stamp=121276
1603

You'll find as an attached file a smaller spreadsheet (JMLC_elliptique.xls) with the cuts one can
do in a plywood sheet in order to build one quasi elliptical horn, a graph
with the frontal view of this horn showing the different cuts is also
attached. You can eventually play on the thickness of the plywood sheet and
apply a scale factor to modify the dimensions of the horn (this means the T
and Fc will change...)

A friend in Germany has the project to use a router to build the Iwata-Le
Cléac'h horn. I give him the spreadsheets. A 3D view of the mesh he will use
for his router is attached.

Best regards from Paris,

Jean-Michel Le Cléac'h