The Subwoofer DIY Page
The simplest of all loudspeaker designs, the sealed enclosure system consists of a driver mounted on one side of a sealed box. The sealed enclosure system is characterised by excellent transient response, good low frequency power handling, smaller box size and lower sensitivity to misaligned parameters when compared to other alignments. However, sealed enclosure systems tend to suffer from higher cutoff points and lower sensitivity than the other low frequency systems.
There are two types of sealed enclosure systems: the infinite baffle (IB) system and the air suspension (AS) system. The IB system normally uses a large enclosure where the compliance (or "springiness") of the air within the enclosure is greater than the compliance of the driver suspension. The AS system normally uses a small enclosure where the compliance of the air within the enclosure is less than the compliance of the driver's suspension by a factor of 3 or more.
Sealed enclosure systems are probably the best starting point for the beginner DIYer because of the relative ease in achieving the desired frequency response. They are usually the subwoofer system of choice for audiophiles because of their excellent transient response (i.e. no boomy sound) characteristics when designed and built properly.
Designing a Sealed System
Sealed System projects on the internet