Whether or not to divide a subwoofer enclosure always seems to be a subject that gets more than its share of controversy. Everyone with even a little box building experience seems to have an opinion on the matter. How much knowledge the opinion is based on varies greatly. In this article I'll share my thoughts on dividing a subwoofer box.
The only time a subwoofer box would get divided into separate chambers is when you have more than one woofer (ignoring bandpass enclosures). A divided enclosure would have one subwoofer in one chamber, with many chambers inside one larger box. There would only be as many chambers as there are subwoofers. Below is a picture of a two chamber enclosure. This box has been divided in half for two subwoofers. One subwoofer would be in Chamber #1 and another subwoofer would be in Chamber #2.
Now compare this to a subwoofer box of the exact same size only without the divider. In this enclosure both subwoofers would share one chamber. This single chamber would be equal in volume to Chamber #1 and Chamber #2 combined.
Assuming both subwoofers are the same and that they both receive the same signal then there really is no difference. Let's say each subwoofer needs one cubic foot of air space. The subwoofer doesn't care if that air space is taken from one chamber or two. If the subwoofers are in a shared enclosure of two cubic feet then they will share the air space between them and each will operate as if it is in a one cubic foot enclosure. That's a fact. But if the subwoofers are not identical and do not receive an identical signal this will not hold true. For instance, if you run your subwoofers in stereo or use different models of subwoofers (neither of which is recommended).
If your subwoofers are identical and they both receive an identical signal then the choice to divide an enclosure is up to you. It can't hurt and I almost always divide the enclosures I build. This is especially true for rectangular enclosures. Enclosures with long sides need to be braced to minimize flexing. Since these braces are going to be there anyway you might as well make one of them a divider. If you can divide an enclosure I recommend it.
If the enclosure is being built with curves such as a fiberglass enclosure I might not divide the box. This is only because the divider may not flow with the rest of the curves of the enclosure. Some people like to see the divider and some don't. Braces aren't generally used in a fiberglass enclosure for the same reason. If the box needs to be strengthened to eliminate flexing then more fiberglass mat can be added.
You should also check out Advanced Enclosure Design and Fabrication. It covers designing enclosures using free computer software, maximizing the output of a subwoofer system, building the box like a pro and testing the output using inexpensive equipment. Click here.