Hi
I crunched the numbers in WinISD for a JBL E-110 and the closed box volume should be 0.437 cubic feet. (QTC = 0.702) Now, this is a net internal volume. So you will need to add a little volume for what is taken up by the driver itself, any bracing and/or glue cleats. Since you are not absolutely sure which driver you are going to use, you could go a littler larger, maybe even as large as a full cubic foot. But, since you are using this as a midrange driver the exact enclosure volume is not as critical as say a bass reflex enclosure for a woofer. What does come into play is the enclosure shape. One school of thought is to go with a tube shaped enclosure or you can go with a box made with non-parallel walls. In any case, the box should be filled with fiberglass to add dampening. Cardboard concrete forms can be used to make a tube shaped enclosure.
Baron030