Subwoofers Explained
About.com has a few technical tips on the different types of subwoofers available for HT use. In the end, this article goes over the different types of subs and doesn't give advice on which type of sub would work best for different types of rooms. If you have any advice on which type of sub works best in different environments, please leave them in the comment section.
From the article:
Crossovers
The crossover is an electronic circuit that routes all frequencies below that point to the subwoofer; all frequencies above that point are reproduced the main, center, and surround speakers. Typically, a good subwoofer has a "crossover" frequency of about 100hz.
Gone is the need for those large 3-Way speaker systems with 12" or 15" woofers. Smaller satellite speakers, optimized for mid-and-high frequencies, take up much less space and are now common in many home theater systems.