First, you must select the placement of your delay speakers very carefully for optimal effectiveness. If the situation permits, significant benefits will occur from first installing the main L&R loudspeakers (or Left, Center & Right — if a central speaker array is also being used), before determining the best locations for the delay speakers.
With the L&R (or L,C&R) main speakers in place, the next step is to play some tracks and walk the room from front-to-rear and side-to-side, listening for where the level starts to fall off and/or vocal intelligibility becomes problematic. You can double-check what you’re hearing by switching to white or pink noise as the sound source, and then employing a good quality Sound Pressure Level (SPL) meter to read the differentials in level from one location in the room in respect to other locations. Scratch out a quick log in a notebook so you don’t forget the measurement readings you’ve taken and where you were in the room.
TIP: When playing recorded sources use tracks that are musically and vocally even in volume, and as consistent in content as possible. When you walk around the room, you want to be comparing apples-to-apples, not guitar solos to vocal choruses. A good CD for this is Bonnie Raitt’s “Nick of Time” but there are many more. Make sure that the program material you choose works well in mono, because many systems will be in mono, and the majority of all the delay speakers, almost by definition, will also be in mono.
So you’ve walked the room, listening only to the FOH loudspeakers and you’ve identified the areas in the room that need augmentation. See if it’s possible to hang your delay speakers where they’ll do the most good. Typical positions are over a balcony (especially very deep balconies), under a balcony, and also side areas that may be in a shadow zone from the main L&R loudspeaker clusters.
Figure 2 — This overhead view shows how delay speakers are used to augment a main center loudspeaker cluster. The delay speakers could be under the balcony, over the balcony, or both. Note that the distance from the main loudspeaker is greater to the side delay speakers than to the center delay speaker; this means that two different delay times will be required (t1 and t2). (Multiple sound sources need to be coincident with one another; the sonic energy from all sources must arrive precisely at the same time at the listener’s location. Delay speakers should always be in line with the main loudspeakers and pointing in the same direction: i.e. towards the rear of the room.)