If you have a home theater, you probably already have surround sound. 5.1 systems are the most popular, featuring three speakers in the front of the room, a pair in the rear and a subwoofer. This served as the de facto surround sound system for the last few decades. Many systems were upgraded to 7.2, with two additional surround speakers and another subwoofer, but the way they worked was essentially the same. If you have a traditional 5.1 or 7.2 system, there is a huge upgrade available to you through your surround sound installer, BRAVAS.
Dolby Atmos is a rethinking of how surround systems are designed, starting with how the tracks are engineered. Sounds are treated as 3D objects, and can be placed anywhere in space that the artist or engineer desires. In your room, speakers are added overhead to help create that three-dimensional atmosphere.