Square/Rectangular acoustic ?

I did once ask on the acoustic guitar forum why guitars were guitar-shaped and besides all the photos of terrible flying v acoustics the knowledgeable answers told me sciency things that covered colins's point about the corners not vibrating and that pinching in the waist controls the boominess by changing which wavelengths can get out of the sound hole - when Martin designed the dreadnought they gave it less of a waist because they wanted more boom than more traditional shapes.

If you look at the evolution of stringed instrument shapes you can see the waist become a feature through trial and error between the medieval fiddles with an oval body like a lute and the renaissance violins made by Stradivari & co that look much as they do today.