whats the difference

Can someone explain the difference in sound between shells made of birch and shells made of maple?

Maple has more warmth than does birch. Of course the size of the shell, model, and coating can effect the sound, maple is just warmer. Birch is not as dense as maple, thus the sound does not have to "go through" much wood so the sound is brighter. Maple muffles the sound more, I suppose you just have to develop your ear to tell the difference. It's like guitarists and their Models and Years issue, I can't tell the difference between a 68 Les Paul and a 69 Les Paul, but that's just me.