Line array speaker systems are most commonly used for concerts, outdoor venues, and large facilities. They are designed to be stacked vertically. The basic idea is that each speaker will have a very wide coverage horizontally, but a very narrow coverage vertically. This will allow one speaker to cover a very wide audience from left to right, without wasting energy by sending sound into the floor or ceiling. Then, by stacking speakers and angling them appropriately, you can get the needed vertical coverage for the entire hall.