Thanks Ken, easy way for the novice builder to work with sound hole design.
It's not square inches of sound hole per X amount of surface area... the equation uses the volume of the instrument, not the surface area, so the shape of the instrument is irrelevant -- hourglass, teardrop, box, little brown jug, bowed psaltery, violin, etc. For dulcimers I use, as a rough guide, the area of 4 American quarter coins -- not as much as 6, not as few as 3.
The shape of the soundhole(s) is irrelevant. It's the square area of holes that matters. Too little soundhole area and the instrument is muted. Too much soundhole area and the instrument sounds "brash". There's a complex formula called the Helmholtz Equation where you can calculate all this is you like partial differential equations. But most of us just say want 2-3 square inches of sound hole area for a 'good' sound.
You can certainly do leaves -- Cripple Creek was famous for their Aspen leaf holes -- and any decent luthier will know how many leaves to get the right sound...
I once built a replica Baltic Psaltery, on which the original instrument had just over 100 soundholes arranged in a spiral design, each hole was a hair less that 1/8" diameter....
