If you wish to stick with the 1" driver I would consider at least 3 different horns:
- Yuichi 480
-
http://www.audioheritage.org/vbullet...ct-preparation
- and last a Smith:
http://www.audioheritage.org/vbullet...-1-quot-driver
At the moment I am using the small Smith horn in one of my systems all the way up. One of the horns rolls off around 15K and the other one around 16K.
The easiest build is the Smith. Since you are not afraid of the building challenge I urge you to build at least a couple of alternatives and report your experiences back here.
IME there are quite different HF response with different materials/finishes. So a mockup in MDF/chipboard usually won't give you the best HF response. You need to either apply a good finish or use solid wood, oiled or varnished.
Johnny