"Enclosure Types:
When laying out a system, you need to decide what type of enclosure to use. Some people believe that a certain type of enclosure can magically increase the output of a woofer. The best an enclosure can do is to allow the woofer to produce what it's capable of producing. A poorly designed enclosure essentially works against the speaker to prevent it from producing its maximum output. A good enclosure works with the speaker to allow it to produce its maximum output. It's also a bit of a myth that bandpass enclosures make woofers produce far more output than other enclosures. They cannot. Look at it this way... If you had a bucket of sand, you could pile it high or spread it out over a wider area. It can't be both tall and wide. There's a limited amount of sand. It's essentially the same with speakers. You can build a bandpass enclosure to produce a tall peak or a wider flatter response. You can't have both.
A sealed enclosure will be the smallest (for a given response shape) and will have good low frequency extension but may not have the best low frequency extension. If space is limited, this may be your best choice.
A ported enclosure will generally have a better low frequency extension for a given response shape (alignment) but would require a larger enclosure. If you made the enclosure as small as the sealed enclosure but ported it to gain the low frequency response, the output would deviate from the desired flat response.
A bandpass enclosure can sound good and give you a flat response but most of the generic bandpass enclosures are not designed for a flat response. They are designed to impress you in the stores. This means that they are built to produce a large peak at some frequency near 60hz. These enclosures will work well with something like rap music but generally won't sound good with other types of music. If you use a bandpass enclosure, it should be designed specifically for your speakers.
If you're building your first system, I'd recommend a sealed enclosure. It is the simplest enclosure and will be the easiest to get right. A sealed enclosure only needs to be the right size and well sealed."
copied straight from
THIS WEBSITE which is a good source of basic information. the type and design of the box in combination with the individual sub determines what frequencies are audible. if you arent getting anything below 45Hz then you are in the wrong box.
what is the point of having a sub woofer to fill in the low frequency audio if you are just going to stick it in a box that totally eliminates the low frequencies and makes it perform like a giant mid bass? you arent even giving the sub a chance to perform based on an assumption which is based on one or two bad experiences with small subs in a ported box.
dont get me wrong, ive had a few bandpass boxes in my days and they sounded alright for some rap and dance music but i got tired of hearing the subs hitting nice and then drop to nothing when the bass went too low even though other normal systems would hit those notes easily. i would rather hear clean bass, barely audible or not, than hear barely audible distortion.