Surround speakers need the bass to deliver realism to the action scenes happening on the screen. That’s why every surround sound is incomplete without a subwoofer in it. The subwoofer provides the bass to the whole surround sound. The bass has to be produced by the subwoofer and not by the speakers. The number 5.1 or 7.1 is the full representative of the surround sound. The number after the point stands for the number of subwoofers used in the system.