To see what I mean, pick up Basia’s CD The Sweetest Illusion. The track “Drunk on Love” features a bass line with a very prominent “growl” or texture. Since there is a lot of mid-bass energy in the recording, it will come through on both the subs and mains. Turn off the mains and listen to it. If the sub is tight, the texture is very distinct and defined, just like it was in the mains. If not, it kind of “runs” together.
Another toughie is the opening track on Basia’s London, Warsaw, New York CD. The bass line has a very subtle texture. You’ll hear it if the sub is tight and well defined. If not, you won’t hear it at all.