Looking for a decent free (or cheap) CAD program to design speaker boxes

After pondering this more, I feel Carlson Hulls is the best program for creating boxes from flat panels. It's made by a CNC mob, and It's free to use for private or commercial uses. The reason for recommending this again is that a ply pyramid made using Hulls will be a monocoque and also a lot stiffer and stable than modelling a furniture making process in a regular program. I have been wanting to show how to do this for a while, but I don't have a valid acoustic design

If there was some sort of horn that can be used to combine 4x 3" full range drivers into a single point source down to about 400hz. Something like that would a good one to demo Carlson Hulls and the build process