Can anyone suggest componets for making a subwoofer addition to my stereo? I would like to put together a box with a low bandpass filter, and maybe a couple subs (8"?) firing forward and rear. I want the nominal impedence to be 4 ohms. It would be nice if it had an amp in it, but I've got two channels open on my Onkyo 8511 receiver if the cost gets prohibative. I'm in college, so the best sound for the lowest price is desirable. I've already got a pair of Speakerlab 7's hooked up, so this is really just a "do it to see if I can" thing. Any suggestions on components or design would be welcome.