Two specific types of subwoofer boxes exist: sealed and vented enclosures. The subwoofer box creates a controlled space for the sound coming from the subwoofer speaker. This allows for peak sound generation.
Venting a subwoofer box allows the sound waves to move from both the front and back of the speaker. This helps to produce lower and deeper bass compared to a sealed box. A sealed box only allows sound waves to move from the front of the speaker, and muffles the sound waves from the back of the speaker.
Sealed boxes are simpler to build compared to the vented variety. Venting a subwoofer box requires more construction time, but may be worth it if you want to achieve a deeper bass sound.