5.1 Surround sound incorporates a Left, Center and Right speaker as well as Left and Right Surround speakers.  A subwoofer is used to output the LFE (Low Frequency Effects) Channel, the .1.


7.1 Surround sound incorporates a Left, Center and Right speaker as well as Left and Right "surround" speakers along with Left and Right "surround back" speakers. A subwoofer is used to output the LFE (Low Frequency Effects) channel, the .1.


New Surround Sound formats such as Dolby Atmos, DTS:X and Auro 3d utilize additional speakers located above the listener.  This creates more depth and a vertical component.