This is a mini Gamewell Diaphone that I designed, it uses entirely 3D printed parts, and I have achieved upwards of 128 decibels from it.

You will only need to print the 5 parts, although you can add a tube for the intake if you wish (however I have yet to design a specific adapter size for it, maybe I will do that later.)

DISCLAIMER: with the height of the horn pieces, you will need at least a 256x256x256mm bed.)

Filament:

I just printed it out of PETG, although I am sure other filaments would work fine (although I wouldn't recommend PLA for the membrane)

Instructions for making:

It is overall very simple, you just need to fit the membrane into the cap (orientation does not matter) and then fit the cap onto the body. This model has 0mm tolerances, so it is supposed to be tight but you may have to sand it down a little. Once you have pushed it on all the way, you can plastic weld the cap to the body. (Because yes, glue is not strong enough)

After you have the main body assembled, you can plastic weld the 2 horn pieces together, (there is only really one way the two pieces can fit together properly) and then you can fit the horn into the main body. (Again, having 0mm tolerances.) Then you can plastic weld the horn to body, and you are done! Enjoy!

Short test: