I haven't personally built a line array, but I have picked up a few tricks on the topic while reading speaker building forums.
- Generally speaking, because there are so many drivers, each one works less hard than normal. They are more efficient. So, in general terms, you probably do not need the absolute best drivers out there, as you would for a 2/3 way or an MTM design.
- Because it is a line array, the upper and lower limits of the drivers determine the top and bottom sweet spots. That is why most line arrays are very tall.
- Line arrays can project a much larger than life sound stage because of their height. That is why you often find that the drivers at the topmost and bottom most are "tapered". This avoids having that 3 foot wide and tall nose on the singer. This is usually done by adjusting how they are wired together (e.g. some in parallel and some in series).
- Some unusual designs actually physically "taper" their drivers by bending the cabinets bend backward, rather than having them stand straight up.
- The interaction between the tweeters and the mid/woofs is critical, and so is their spacing from each other. So you will likely see tweeters recessed in the baffle to avoid unwanted reflections off a faceplate edge and such. So pick your drivers with care to ensure they can all be recessed flat to the baffle.
You are going to be cutting a lot of holes, and to avoid combing effects from a line array the measurements need to be pretty tight. So measure thrice and cut once.
Enjoy,
Bob
