Sealed, ported, and vehicle-specific subwoofer boxes, sized to the airspace your subwoofer actually calls for.
Tuned-port boxes for maximum output per watt. Larger, and built to a specific tuning frequency rather than guessed.
Airtight boxes for tight, accurate bass in a smaller footprint. The more forgiving choice when exact volume is hard to hit.
Enclosures shaped to a particular truck, SUV, or car cavity so they use the space without compromising the airspace.