On another note, I did what your talking about once. A friend moved to FL and gave me a sub and box (10" jensen nothing special) and I had a cheap amp left over from my trial and error audio days. All I did was go out to radioshack and picked up a 12v power supply for about $25. It worked out nicely.
If you want good sound in a dorm room I suggest going out and getting a speaker system with a sub for your computer. You will be amazed what those speakers can produce, especially in a dorm room.

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