I think the less harsh corners the tighter the sound so I wouldnt go with a star, too many hard corners. If you look at the SPL boxes they seem to even round the inside corners of the 90degree angles by putting an inverted triangle in the corners.
yeah that'd be called a backwave board bud. it's amazing what wave alignment and backwave cancellation can do for an SPL score. So far I don't think anyone's response has been remotely serious.
To the thread starter, as stated the more sharp corner's a sound wave has to travel around the lower your SPL, keep it simple, smooth, well braced, and sealed(not a selaed box but no air leaks).
I was looking into doing a Triangle shapped box... (90 degree trinangle... with the L shapped side against the back of my seats... and the angled side aimed toward the back of my tailgate (that is where the sub would be... and the amps)