IMHO the B2-50 has little actual power (in db's) below 30hz (or above for that matter). There is only so much you can get out of that little box. It poop's out early.
If you have a speaker that is putting out bass that is, say, only down 3db in your room at 28db you really don't need more. It would/could/should still be putting out some substantial 20hz bass. There is very little if any musical info down there except for the very bottom organ notes. And in using it, or any sub for that matter, with a good full range speaker, it just puts out too much info in the frequencies your full range speakers handle unless you have a really sharp slope on the crossover. I wouldn't use a sub unless I have a need for bass reinforcement for inadequate or uneven bass caused by speaker placement.
If you have a speaker that is putting out bass that is, say, only down 3db in your room at 28db you really don't need more. It would/could/should still be putting out some substantial 20hz bass. There is very little if any musical info down there except for the very bottom organ notes. And in using it, or any sub for that matter, with a good full range speaker, it just puts out too much info in the frequencies your full range speakers handle unless you have a really sharp slope on the crossover. I wouldn't use a sub unless I have a need for bass reinforcement for inadequate or uneven bass caused by speaker placement.