Explanation of Biradial horns

[Gubbe]

Could someone explain the the math or how the curves are generated for Biradial horns?
I understand the first section of Biradial JBL horns, up to the diffraction slot, but how are the curves that give the horn it's shape generated from there?

 

[grindstone]

Not that it's concrete, but the JBL 4430/4435 paper (courtesy of Mr. Keele) has a vague hint and you'd probably have to work backwards from those horns. FWIW.

 

[GM]

FWIW/YMMV, etc., I've reverse engineered a number of horns including Altec's biradial sectoral, CD horns from the beginning of the horn (driver horn where appropriate) same as any other horn, so at a glance see no reason why his can't be either with the info available.