Anybody know anything about subwoofers?

I just finished installing a complete Alpine system in my Dart, and I'm having trouble with the sub. I have a 12" Alpine type r sub, with a Alpine mono block amp, it works, but it is only putting out about 1/10 the volume it should be. I hooked up my Ipod directly to it and it cranks. I've triple checked the settings in the head unit ( alpine idx-303 ) and everything seams right, what am I missing?