I needed to find a dual 12 inch box for my subs fast. I had already purchased my subwoofers and now I had the chronic addiction of hearing my subwoofers pound inside of a box. There were so many different variables that I needed to look at and decide. I have made a small list to help anyone that is looking at buying a box for their subwoofers that will sound the best.
The first variable you want to look into is, what type of sound do you desire to get our of your subwoofers. If your looking for the deepest sound inside the car that is crisp and quick as possible, you want a sealed box. Sealed boxes are just a box that is sealed and has no air gaps. These have been around for ages, and are very reputable to go with.
If you want the bass to be heard from other people outside of your car and as far away as possible, than a vented box is more your style. Vented boxes are somewhat new technology and are said to be double the loudness in a lot of instances. Your subwoofer will have special specifications of what frequencies the port or vent should be tuned to.
The box can make or break how loud your system is, so it's a huge deal. I have seen the cheapest car audio equipment sound ten times louder than a guy that spend thousands because the box was better designed. Look into what box best suits you and your subwoofer. You may regret it, if you do not make the correct choice from the get go.