Match The Right Sub(s) To the Space

Here is the method for matching the subs to the space:  

8" -    .7-1.0 cuft

10"-  1.2-1.5 cuft

12"-  1.7-2.5 cuft

15"-  3.0-4.5 cuft

The port formula for the above box sizes is as follows: 15-16 square inches of port area per cubic foot of box volume, make the port 13 inches deep. The port is tuned to the box volume, not the subs, and tunes to 45hz (about right for SPL & daily driving).

Once you determine how much space you have available, divide the sub(s) into that space. Don't cram the space, its better to error on the big side than the small side.  A 10" sub will outperform a 12" sub if the space isn't enough.