If you're not working in larger venues you may not have heard of system delay and if you have you may have thought, "Why do I need it?" Well, even in a small venue it can do a lot to make your life easier. What I'm talking about here is adding delay to the main outs, or to feeds to remote speakers.
Remote speakers, often called "delays" need the delay so that sound coming out of them arrives at the same time as the sound from the main PA. Setting it up is just a simple matter of determining the distance from the mains to the delays and punching in the right number of milliseconds. Even in a small venue adding some delays can be a big help. In a boomy, reflective room, adding a pair of pole speakers about two thirds of the way back can let you mix with the main PA at a lower volume and still have good coverage all the way to the back.
But the real reason I brought this up was to talk about putting delay on the main system. In a small venue the main reason is getting the drums and amps in synch with the PA. If the audience can hear the original sounds coming off the stage, those sounds can actually arrive after the sound from the PA. Hitting the listener at a different time can cause phase issues like comb filtering. The way to solve it is to figure out how many feet the mains are in front of the back line and add just that much delay. That way all the original drum and amp sounds arrive at the listening area at the same time as the sound from the PA. Nice and clean.
Even in larger venues, the drums themselves might not be an issue, but the sounds from the drummers humongous monitors can be. If you're looking at a drummer sitting in a pair of Texas Headphones (dual 18s and tops on either side of him) that's a fair amount of sound coming at you from up center. Adding the appropriate delay into the main system can put all that sound back in synch.
So whether you're in a large venue or small, outdoors or in, taking a look at arrival times can help you adjust things for the cleanest, punchiest sound possible with just a few milliseconds of delay. Give it a try!