Has anybody built their own subwoofer?
 

I have a 4x10 and a 1x15 combo amp at 900 watts total. The amp itself however, is a 1200W amp. I have a six string bass, with the Low B tuned down to Low G# with a .160 gauge Low B string, and an Electroharmonix Pitchfork pedal that allows me to shift my tuning down as low as 3 octaves. I don't wanna blow my **** out, is the thing, and so I started doing a little bit of research and found out that Electroharmonix makes a channel splitter adapter pedal to use to add on an additional speaker cabinet, so I want to use the alotted 300W available by building a subwoofer, and just letting the box do the work by putting a 1x20 in just a big box. Has anybody tried anything like this before? and where do I go to start researching how to build a subwoofer?

Look into limiters. They'll keep it from overloading and blowing those current combo's, and would be a cheaper/quicker option. As far as building a sub, there's tons of references out there.

Thanks! :D