Here is an article from Sound on Sound from March of 2006 explaining line array speaker systems. More and more touring musicals are using line arrays for their main and center cluster speakers. While rock shows tend to use them in long hangs, theater shows sometimes use them in blocks of five and six for zone coverage.
Get up to speed on the principles behind line arrays.
The solution is to devise a loudspeaker that is tightly focused in the vertical dimension but spreads sound widely in the horizontal dimension. To do this, the speaker needs to be large vertically, but small horizontally. Like a column, in fact.