A bed can be thought of as a traditional channel based 'stem' with the rules and expectations of those configurations (3.0, 7.1 and the most common 5.1). These are fixed locations in space that are tightly constrained to traditional speaker environments, this includes theatrical environments where a speaker array might be used. In Dolby Atmos, the largest bed configuration that exists is 7.1.2 which allows for Left, Center, Right and LFE along with Left and Right Walls and Left and Right Rears plus an additional overhead stereo pair Overhead Left and Overhead Right.