DIY JBL Drivers?

I have the following drivers to use:

3x Jbl 2121H (cant find specs. have a frequency response sheet that comes with.)

2x Jbl 2118h http://www.jblpro.com/pub/obsolete/2118.pdf

2x 2402 http://www.jblpro.com/pages/pub/components/2402.pdf

I also have two JBL 3105 crossovers http://www.jblpro.com/pages/pub/obsolete/3105-3115A.pdf

My main system is lacking bass. The bass line is hard to distinguish at normal volumes. anyone think i could put the third 2121h into some sort of enclosure as a subwoofer?

As for the rest of the drivers, from looking at the frequency response graphs of the 2121h and 2118hs, I think it would be better to build a two way with the 2402 tweeters and the crossovers which are optimized for the tweeters. Im not too knowledgeable of speaker enclosures or frequency vs decible graphs and their qualitative values. anyone know if it would be worth it? I have all of the equipment available and my father has the woodworking and design blueprint knowledge to fashion the enclosures. I am a bit better with the physics of it.

I would post this question over at Speakers or at Lansingheritage where experts like Zilch and GordonW hang out. The 2121H is a midrange driver and does not go low enough (only to around 250-300Hz) The 2118H would go lower but I am not familiar enough with it.

Hi. I want to buy 2 pieces. JBL 2121H