When I first built the bass horns about 20 years ago they were primarily lath and cement/stucco construction with some brick/block work in the backchamber portion. While messy, the lath and cement is a pretty easy way to shape a big horn and the density is a big help too.
When I re-worked the room for the Cogent system I demoed the original cement mouths and reconfigured them a bit with the new hardwood mouths. The wood is a Brazilian species called Garapa and it is extremely dense and hard.
Drivers since the beginning have been JBL K151 alnico 18". Since I added the active low-pass and EQ to boost the 20-30Hz range I've been worried about over excursion. I have a pair of Gauss 4882 driver waiting to be installed which have greater power handling a double the excursion of the K151s.
eso