Check out very this recent article from MIT on the evolution of the shape of the F-Hole.  A link to the MIT news post is here, and the research paper is here.

“Researchers found most of the sound produced from the violin and its ancestors flows through a sound hole’s perimeter, not its interior.”

Some interesting conclusions from the paper:

• The researchers found that a key feature affecting a violin’s sound is the shape and length of its “f-holes,” the f-shaped openings through which air escapes: The more elongated these are, the more sound a violin can produce.
• The thickness of a violin’s back plate also contributes to its acoustic power…. A thicker back plate, they found, would boost a violin’s sound.
• Throughout the 800-year period the researchers examined, they noted an evolution in sound-hole shape — from a simple round hole to a semicircle, which eventually morphed into a c-shape that grew more elongated, ultimately assuming the f-shape of the violin. The perimeter of these shapes steadily grew, while the area of the interior void gradually decreased.

Very interesting research which will no doubt create a series of new experimental violins with further elongated sound holes.