ah...this might help:
http://www.sonicdesign.se/horncalc.h...onsiderations.


...or maybe not... am still looking for good input for non-rectangular (conical) horn geometry.

like the pic below.

And here are some considerations when building a conical horn that resembles the old gramophone more thatn what this project is about: http://steinmusik.de/horn/artikelee.html - still nice reading.

cheers!