While the rb5 is rated that low it drops off noticably well before then. Setting the sub a bit higher will pick up before the rb5's run out of steam. Not knocking them understand, but many speakers are rated to go so low, and they can, but not at the same volume level as lets say at 100 hz. It a setting you have to play with since how high they are off the floor, how far from the wall, what kind of room acoustics etc, all affect the sound of them.