The precedent effect states a few things that are important to us in the audio reinforcement realm.

http://en.wikipedia.org/wiki/Precedence_effect

“The precedence effect or law of the first wavefront is a binaural psychoacoustic effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener’s echo threshold), listeners perceive a single fused auditory image; its perceived spatial location is dominated by the location of the first-arriving sound (the first wave front). The lagging sound also affects the perceived location. However, its effect is suppressed by the first-arriving sound.”

In a nutshell, when two signals arrive together they act like a single signal. When one arrives first it’s perceived as the origin of the signal even if the secondary signal is louder.

This has many important implications for live sound.

IF the PA is in front of the band & IF the PA signal arrives before the direct signal coming from the stage (guitar amps, drums, bass amp, etc…) the origin of the total sound will appear to come from the PA.

IF we delay the PA (using DSP) back to the physical backline or further, the sound origin appears to come from the stage instruments.

I have seen suggestions that we should delay the PA to the drum kit, guitar amps, etc…

Since a drum kit is a 3 dimensional instrument (has height, width & depth) * a guitar amp will typically have a single dimension, I would be inclined to delay to the middle of the drum kit.

How?

The best way is to place a speaker at the center of the stage on the line at which you want to delay too. Use that as your (0ms) measurement & then delay the PA until it matches. It’s amazing what a difference doing this simple delay procedure makes in focusing the audiences attention to the band & not the PA.

Here is the basic procedure:

Place reference speaker at center stage
Measure pink noise through reference speaker with mic placed out in the house & note delay time
mute reference speaker
Send pink noise thru PA & measure (same mic position) and note delay time
Compare reference speaker delay time with main PA delay time
Delay main PA until it matches delay time of reference speaker

If you can’t measure, don’t have a reference speaker or simply don’t have time, you can guess how far back the reference line is and delay accordingly. If when you look up & listen to the band @ sound check, you feel the main PA is either too late or still too early, adjust & listen again.

Keep in mind that in this day and age of digital consoles & digital signal processing, there is an inherent amount of latency by default. Typically your reference speaker wouldn’t be fed a signal from the main PA DSP so there is latency involved with the main PA that might not be involved with the reference speaker signal. For example, if you fed the reference speaker off an aux or matrix that bypasses the main PA DSP device. In that case, one system has more inherent delay than the other. Something to keep in mind.

Due to digital signal latency, you may find that the main PA is already arriving late enough that there is no need to add further delay to the signal to align it with the reference target point. If so, fine.

If a signal passes through enough digital processors in route to the speakers, you could easily find that your PA is significantly behind the band’s backline gear already. If so, there isn’t much you can do but physically move the band or the PA.