A cone has apex $S$, and edges $S A , S B$ are mutually perpendicular. The angle between $S A$ and the base plane is $30 ^ { \circ }$. If the area of $\triangle S A B$ is 8, then the volume of the cone is \_\_\_\_ .
A cone has apex $S$, and edges $S A , S B$ are mutually perpendicular. The angle between $S A$ and the base plane is $30 ^ { \circ }$. If the area of $\triangle S A B$ is 8, then the volume of the cone is \_\_\_\_ .