I'm building the second horn for my RCF Nd1710 mt3 audio driver, 1" exit , 108db/w/m, 1-20khz range, titanium diaphragm and strong magnet.
The big boy is a 130mm round bar, normal aluminum that melt on tools
I chose tractrix contour, I tried it many times in the past, it works perfectly for home use for middle and high frequency.
Probably I will buy a good finishing tool
Some pictures of the horn , still work in progress