Okay wow great stuff here. I just made three slate calls. The first I used exactly 1 soundboard thickness, and the other two I went a hair under 1 soundboard. The the last two are certainly higher pitch, but the first is black slate and other two are are green and purple slate. All over glass. I would think that the distance between soundboard to surface distance (let's calls it STS) alters the wavelength of sound, getting high and low pitch? Closer together high pitch, farther apart low pitch? But like Steve said, if I switch strikers I also get different pitches, but they seem to stay within a specific range relative to each call. For example, if I use a maple striker on my black slate and green slate, the back slate is lower pitch that my green slate, and then if I switch to a locust striker, although I get a different sound out of that striker, I still have a lower pitch black slate, and higher pitch green slate. I suppose the different types of slate also make difference too. I guess I just need to start making more calls

I'm making some calls for people for super cheap while I figure them out so maybe my next two will be exactly 1 soundboard thick STS and then slighter over 1 soundboard thick STS, both same woods and dimensions otherwise.