Mistery Woofer
Radioshack did that a lot. I think this woofer was a replacement for an "all in one" rack system. Maybe someone ordered a set, and never picked them up. That's how I got mine, so said the RS employee. Bought them on the "discount table" they had set up.
I had these a very long time ago as replacements in a set of boxes that were about 1.5cu ft in volume. I always thought that the box was too small to really make use of the woofers potential.
The bass was ok, but there just wasn't the punch and low extension I thought these were capable of. Just to clarify, they were in sealed, 2way boxes. Not sure if they were intended for a ported box or sealed.
I really don't think this driver could or should be used as a sub. It is a woofer by design. It is a single VC . That being said, if you want to experiment, I would start at about a 2 1/2 to 3 cu ft sealed box. This size should be large enough to produce low bass, but at a cost of max power handling.
A box sized 16x12x24 will get you about 2 1/2 cu ft. Filling the box with loose fiberglass would also help.
What plans do you have for the amp to drive this? Most sub amps are 4ohms. Since this woofer is 8ohms, Be aware that the output from the amp will be cut in half (or more). This might work:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-784
Good Luck. Have Fun