Here’s an interesting tip for live sound engineers, particularly those who find themselves working in small to medium-sized venues with a full PA and bands with quite a bit of stage volume. Have you ever noticed how much better you can sometimes get things to sound when you have the band turn their stage volumes down really, really low? You’ve probably also found that they aren’t willing (or even able) to play at volumes low enough that the PA is the only significant source of sound for the audience. Most sound engineers believe this is an insurmountable problem, but once you understand the full nature of the problem you’ll find it may not be. Some engineers put the drummer behind a Plexiglas barrier, which can help quite a bit because it both reduces the direct drum sound from getting to the audience and potentially overpowering other things in the mix, and it reduces drum leakage into other mics on stage. This is a valid technique, but only addresses part of the problem.
Part of the answer lies in the philosophy that the sound system is really intended to “reinforce” the sounds on the stage. Ideally a sound system is transparent to the audience, allowing them to focus their attention on what’s happening on stage without being distracted by the perception of sound coming from some other source. What we find in practice is that the two (stage sound and PA) fight against each other to some extent. Part of this problem is because of the time alignment (or lack thereof) between the two.
When your PA is positioned a typical 10 to 20 feet (or more in some cases) in front of the sound generating elements on the stage, you essentially end up with a delayed version of those sounds reaching the audience. They hear the PA first, and then the sound from the stage gear a split second later. Though the delay is typically only 15 to 35 milliseconds (for a rough estimate you can assume approximately 1.5 to 1.75 milliseconds per foot of distance) the overall impact to the sound can be quite significant. Generally the delay time is short enough, and there are enough other time arrivals due to various surface reflections, that you’ll rarely hear this as a discrete echo. Nevertheless, you will find that delaying your sound system sound by enough to better align it to the sounds coming from the stage can often clean up a lot of the mud and provide more, punch, clarity and intelligibility while making it easier to run at lower volumes when you need to. This is specific form of Time Alignment is sometimes practiced by savvy sound engineers.
It’s absolutely worth trying, but your results may vary quite a bit based on several factors. First, understand that we’re talking about running your entire mix through a delay unit. Don’t skimp on quality here. It’s easy to do more damage than good. It can also be difficult to get the delay time set properly. Not only do you need a delay that can deal with very small increments of delay time, but you also need some reliable way of estimating or measuring the delay you’re trying to fix. We’ll assume you don’t have any sophisticated measuring equipment that can show you multiple arrivals of sound at the mix position. This is what the “big boys” use – they may have a tech hit the snare drum and then they’ll look at a readout that shows the arrival of direct sound from the PA (left and right stacks may be different), the sound coming directly from the stage, the reflection of the monitors off the back wall and/or ceiling, and the onset of reverberation in the room (not necessarily in that order). From there they can usually tell how much to delay the PA, or if it will even do any good.
The “poor man’s” method involves some measuring of distances, guessing, and listening. Ideally, you’d be set up so the stage amps are pretty much all the same distance away from the audience as the drum set. You can then make a distance measurement of that and compare it to the distance between the PA and that same spot. Let’s say the difference is 15 feet, for example. Multiply 15 x 1.75 and you’ll have a pretty good place to start in terms of delay time (in this case 26.25 ms). Have the drummer play and then move the delay time around that value and see what happens to the sound. Keep in mind the speed of sound is not fixed. It varies slightly with different environmental conditions (air pressure, etc.) so your math may be more or less accurate from day to day. If it doesn’t seem to make any improvement don’t give up. It may be that the venue you are in just has too many reflections to hear much benefit. Try it in a few different circumstances.