My brother asked me to fabricate a folded bass horn for his Christian rock band. Beings that work is slow (I'm a remodel contractor) I couldn't resist diving into this project.
I used Hornresp to design a decent horn that covered the 35hz to 150hz spectrum. I made the outside dimensions 45" x 45" x 25.5" so it would be easy to transport. I used a pair of Eminence Lab 12 drivers (available from Parts Express) and 3-1/2 sheets of 3/4" plywood. I glued and screwed the plywood like it was going out of style.
The completed horn just blew my mind. First, it's beautiful (you can see it on my home page), second, it's powerful--I'd forgotten how efficient a front loaded horn can be. Third, its low end range far exceeds my expectations--it has no problem hitting hard down to 20hz. I never expected this. I'm so pleased with the outcome, that I'm going to offer it as standard wares for sale on my web site.