Figure 4 — This image depicts the use of a Front Fill delay speaker and an underbalcony delay speaker. Both are timed back to the original acoustic source of the lecturer standing on stage, as is the main loudspeaker cluster. Timing to the original source is good practice whenever possible. It improves, clarity, intelligibility, and especially imaging. (Illustration courtesy of Roland Highham).
If you MUST set delay times by ear, use an electronic metronome to generate a short pulse. Energize the main loudspeaker cluster and the delay speaker simultaneously. Listen for the ‘double clicks’ as you adjust the delay time. When they fall directly on top of each other and you here only one click, that’s your starting point. However, it’s common to be off by quite a few milliseconds, even if you’ve trained your ears carefully. While it can be difficult to hear when the delay time is set dead-on, it’s not hard to hear the unwelcome side effects when time delays are set wrong. Without the use of precision measuring equipment, few people can get within 5 ms of accuracy.
TIP: If you cannot set the timing by ear and have no access to instrumentation equipment, you can measure the distance between the main speaker system and the supporting delay speaker. Sound travels at approximately 1.1 feet per millisecond, varying fractionally with atmospheric conditions. Therefore, if you’re able to measure the physical distance between the main loudspeaker and the delay loudspeaker, you can come quite close to deriving the proper delay time.
That said, vector geometry cannot be ignored; if the delay speaker is far overhead and the path length from the main loudspeaker to the listener — and the delay loudspeaker to the listener — are not consistent from seat-to-seat, there will be no correct delay time. It’s then up to the system technician to arrive at the best compromise. In almost all cases, this means setting the delay time to favor the seating areas that are closest to the delay speaker, as they will be the areas that are most negatively affected if the delay time is off the mark.
Ken DeLoria is Senior Technical Editor of Live Sound Magazine and a truly big fan of delays speakers. He has taught comprehensive sound system alignment techniques for more than 20 years on three continents.