DB = decibels it is the standard means of measuring how loud something is..airplanes..stereos etc.etc
A subwoofer is a speaker (transducer) that plays frequencies lower than most musical instruments or voices can go.. Lower harmonics... If that doesnt help ask the schools music teacher or band instructor..
Hertz = is the measurement of frequencies low numbers like 25 hertz would be played by a subwoofer.. 15000 hertz would in the range of a tweeter.
Watts is a means of measuring electrical power..A library would have better explanations than I can give you.. I know the how and why but explaining it would just confuse you..at least coming from my fingers.
As for the differences in enclosures there are pros and cons for all of them.
Sealed.. Is generaly very tight and accurate but lacks in the lower frequencies.
Ported is louder and will play lower than a sealed encl. but also isn't as accurate and uses a larger enclosure.
Aperiodic enclosures Use small enclosures like a sealed but with a thin mmbrane that resists the movement of air from the speaker. Most often you need a specific size of the aperiodic material for a given enclosure size...anyway it give you tighter bass than ported but also plays lower than a sealed.
Bandpass enclosures are basically a hybrid.. both ported and sealed simultaneously..They are more sensitive to wattage ( less power to creae the same volume) The downside is that they have a very narrow frequency response..
Anyway hope this helps some..let me know how the report comes out.
Your friendly neighborhood subaru freak!