How do you tune a subwoofer enclosure?

Question

and how do you know?

Answer 1

The tuning frequency of the enclosure is found by knowing the internal volume of the enclosure, the cross sectional area of the port, and the length of the port.  If you what you want frequency you want to tune your enclosure to then you only need to know two of these to figure out the third.

Usually the length is the one out of these three that is found out last.  What frequency you are tuning should be found out either by manufacturer's recommendations or by designing an enclosure in a design program.  Once you know what frequency you want to tune to you will need to know the cross sectional area of the port.  This is determined by how much air velocity is going through the port as well as the space available.  You want a air velocity through the port low enough that you do not have port noise.  You can figure out what cross sectional area to use the same two ways as the tuning frequency.

Good Luck!!!