Software that allows you to input your driver's thiele/small parameters and plot frequency response curves based on different types & sizes of enclosures. It'll even calculate box dimensions for you. Steep learning curve, but an extremely powerful tool.

Give me the specs to that Nakamichi sub & I'll prove it . . . . . Diamond Audio recommends a ported 1.5^3 enclosure for it's 12" M3. I had to double that in order to get the best performance out of it.