In 1949 Helmut Haas identified a psychoacoustic occurrence; i.e. whatever sound source we hear first will be that which catches our attention. In practical terms, you’ll normally want the audience to pay attention to the stage rather than having their attention drawn to the nearest delay speaker. So it’s a good idea to add a few extra milliseconds delay to each delay speaker, but only after first arriving at the technically accurate delay time that perfectly aligns the delay speaker with the nearest “main” loudspeaker that it is intended to support. Keep in mind that in a large convention hall or ballroom, there might be a need for as many as three or four rows of delay loudspeakers placed in locations that progressively move rearward toward the back wall of the room.
TIP: It’s not uncommon to see system techs adding 10, 15 or even 30 milliseconds of additional delay time in an effort to make the delay speaker “disappear” sonically. However, it only takes 1 or 2 additional milliseconds to make a delay speaker become acoustically invisible, if the precise delay time has first been set with pinpoint accuracy. It’s quite a revelation to add only a single millisecond of delay and then experience the delay speaker sounding like it was just turned off. But of course it’s still there, dutifully doing its job, and that’s what you want.
In rare situations, it may occur that the sound system is too “dry” or too “tamed” because it’s been impeccably installed, tuned, commissioned and all delay times have been precisely set. Given an optimal system tuning, it’s sometimes possible to make an opera in a sports arena sound like its taking place in a small room. While this is not an everyday problem, it does indeed happen from time to time.
A quick fix is to add a bit of extra low-frequency energy, which will invariably excite the room’s reverberant field and start making things sound ‘bigger.’ Another fix is to increase the delay time of the delay speakers by 5 to 10 milliseconds. You must be very careful not to destroy intelligibility, but if a bigger, rounder sound from the orchestra and vocalists is what’s required, that’s one way to achieve it without resorting to adding artificial reverb. Letting the room resonate naturally is usually the best way to achieve optimal sound quality, but not always. If the room has an inherently harsh or muddy sonic signature, then using a high-quality digital reverb will likely be the better choice.