I'll try to explain this the best I can, it's a pioneer fh-x70 bt unit (I think) the sub cntrls are: subw:50hz,63,80,100,160,200(+6 or -24 which eliminates any bass at all and acts as a 2nd gain control actually, and a -6/-12 setting next to it that (im guessing) adds a slight bass boost)...