Workflow

Steps necessary

The project splits up into supprojects: Building the actual horn and building a mounting platform.
Material of choice would be fiber reinforced plastics laminated to some kind of foam core. This way one get's a lightweight structure with controllable stability characteristics.

The first step, building the horn, is quite easy, as you've only have to get the scale right. As always size matters. Especially with part two, as the whole idea of the platform is to provide stability by closely matching the geometry of the head.

As it's the 21 century and the head is too damn high above the ground to simply form a plaster mould, the way to go is making a 3D scan of the head. A Microsoft Kinect camera + the right software will do.
This way we'll have the geometry to construct the platform.
Ok, it's not as easy as it sounds, as we don't have a cnc-machine around, that could automatically get a real model from the digital data. We don't have a 3D printer either, but frankly the dimensions won't fit the regular ones those geeks out there are playing with.

• 3D Scan the head to design the platform
• Software postprocessing
• Building a model of the important parts of the head from the digital geometry
• Use the model as a mold to create the platform
• Installing means for stripping down the platform, attaching some kind of string to it.
• Fitting the horn to the platform

Even though it won't be visible afterwards, the modeling part will be the most time consuming. But the investment into precision will definitely pay off.

A first glimpse at the topology of the head:

The hole under the hair thingy would be ideal to route an attachment string through. And the plain head above the eyes should be wide enough to provide good transverse stability.