Understanding the Isophon HornKhele

[Tyimo]

Hi!

After that I understod the Replikon BLH design from Klangform Akustik (thanks for Till and Raffi!) I would like to understand an even simplier design: the Isophon HornKhele.
It was a very popular loudspeaker because of the sound quality and the simplicity. There are some another firms who also built similar loudspeakers, for example the Impulse.
I listened the Impulse H6, and couldn't believe that it can sound so nice! With the speaker design programs what we usually have I cann't simulate these loudspeakers, because I always get ver-very bad responses, but in the reality the sound is very nice!

My first question:
Is there any equation to calculate a BR port with Expo-Horn shape??
Second:
Is there anybody, who is experienced with these loudspeakers?
Third:
How could I design a HornKhele for my driver?????

Greets:

Tyimo