Choosing the right subwoofer can be difficult, but it is easy to underestimate the importance of a quality sub-box enclosure. Depending on the type of subs you have, the sub enclosure can make or break your audio system. It is important for anyone looking to upgrade his car audio system to install subwoofers for that extra-needed bass.
Get familiar with the type of sub boxes that are available: sealed; ported; and bandpass.
The reason sealed subs are called sealed is because there is no way for the air to escape out of the box. Because no air can leak out of the enclosure, it requires a higher-watt amplifier to drive the subs. One of the benefits of a sealed-type enclosure is that it is excellent for producing bass at low frequencies. For anyone who demands deep, precise bass for hip-hop-type music, sealed boxes are the way to go. However, because no air can escape the box, a sealed box is less boomy and will not sound as good when playing other types of music, such as rock or jazz.
The next type of sub box is a ported or vented enclosure. A ported box has a port or a vent on one side of the box to allow air to escape, producing a boomier sound. A ported sub box is recommended for anyone into hard rock or metal, which require a higher musical output. The port is tuned specifically to the volume of the box and the performance of the sub. If you are considering a ported sub box, make sure your subs match the requirements for the enclosure. Also, because the port has to be accurately tuned to the dimensions of the box, you shouldn't make a ported box on your own unless you have a firm understanding of volume and dimensional measurement. Because of the port, it is possible for a ported enclosure to be louder and have more bass than a sealed box. However, the size of the box has to be much louder than the size of a sealed box.
Bandpass boxes are a mix between sealed and ported boxes. A bandpass enclosure has two chambers. One chamber is sealed, and the other is ported with sound waves coming out of the ported chamber. Because of the combination of both sealed and ported boxes, bandpasses are excellent for all types of music, from rap to classical. However, the subs usually come with bandpass boxes. Be careful when choosing a bandpass because the subs that are built into the box are not always tuned to the frequency of the port. A lot of deals seem like a steal, do your research or you might be robbing your system of quality sound.
It is extremely important to get a box and sub tuned to each other's frequency. It is also important to get a box that fits the dimensions of your boot. If you drive a car that has a smaller boot that cannot fit the recommended box for optimum performance, adding poly fill to the inside of your sub box will allow your enclosure to act like it is much larger than it really is. This is recommended only for sealed boxes that are below the recommended size of your boot. Poly fill helps deaden the back waves travelling from the back of the speaker that produce echo and distortion. It is not recommended to add poly fill to ported boxes, because it can interfere with the frequency tuning of the port.
If you are not sure what subs and sub boxes are right for the dimensions of your car boot, consult a car audio technician.