Not that there are many passive subwoofers these days, but I'd thought I'd share how mine is powered. Instead of connecting the main L/R speaker outputs of my receiver to the inputs of the subwoofer, and the speakers to the subwoofer, I have my Yamaha receiver's subwoofer output connected to a 25+-year-old Harmon Kardon amplifier (bought it from a friend a few years ago for $15). The combination produces some nice foundation-shaking bass.

http://media-convert.com

Description from their web site:

Why use Media-Convert ?

Simply because Media-Convert is the best manner of converting audio files, video, presentation, document, spreadsheet, etc.

Media-Convert advantages :

Since I've been doing radio spots for my work, it was only natural for me to also record our telephone "Event Line" (a listing of our upcoming performances). Naturally, I figured that simply using the same method I'd been using for the radio spots should work fine, with the addition of holding a phone or headset up to a speaker. The results were less than spectacular, to say the least.