The right dimensions is definitely the key to a good call. Everything comes in play, just like Joe says, distance between the ledge and the top of the soundboard, start at twice the thickness of your piece, which is usually 1/8" thick I start by taking two 3" pieces of glass and laying them on top of the pedestal and work it until the top piece is level with the ledge. The distance from the top of your floor to the underside of your slate is important too little will kill the resonating also too far away will produce such an echo it will over ride the break. Also the inside wall configuration is important to me, as I like to concave mine I feel it allows the sound to bounce uniformly around the pot insides. Thickness plays important part for the vibrato of the call too. A lot of stuff isn't it? And not even half way there....just start experimenting, pay close attention to your measurements and write them down when you get it when you feel comfortable with the sound. Another thing, before your glue sets up you can also do the tap tests, tap the center to the slate and listen to see if the sound is crisp with a slight echo or if it is dead, either way, you can remove the slate or leave it in place.
