A subwoofer box is an enclosure that houses the subwoofer. It is a hollow cabinet where you place the subwoofer of your sound system. Different subwoofer box designs are available, starting from simple sealed box structures to complex structures with baffles and horns. A subwoofer box protects the speakers from the vibrations of the subwoofers. Even though the vibrations may not affect the speakers in the short term, there are always long-term issues seen with speakers. Not just the speakers, the box protects the subwoofer from over-excursion, which is self-destructive. Besides,  a subwoofer box enhances the subwoofer's output by reducing the out-of-phase sound when tuned with speakers.