Mains, Delays, and Fills
The first major difference between concert and conference is the way an engineer thinks about the relationship between the mains, fills, and delays. In a typical music concert production, the mains are exactly what the name implies– the main speakers which supply the bulk of the sound in the room/space.
These are supplemented by delays if the room/space is large enough and front fills if there is a significant hole in the coverage for the first few rows. Larger gigs and/or oddly shaped rooms might have any number of other fill speakers such as out fills, back fills, etc., but the point of all of these fill and delay speakers is to supplement the output of the mains.
Fig. 1 depicts a typical PA design for a musical concert.
The mains are just offstage, downstage of the performance. To fill in the gap in coverage between the mains, small front fill speakers are used either on the lip of the stage or just in front of it.
Small delay speakers are out towards the back rows, time-aligned with the mains to reinforce coverage. Side fill or out fill speakers cover the sides of the stage not covered by the mains.
There are large screens on stage, but the content on the screens is not crucial, so it’s OK that the view is partially blocked for many in the audience.