FRONT of HOUSE • November 2018 • Sound Sanctuary: Dispersion

Getting great coverage to every seat in your church is no small task, and requires a great deal of time, energy and money to get right. At the end of the day, there simply is no way to have every seat in the house get the exact same mix. Attempting to achieve that is futile, and one could waste enormous sums of money in the pursuit of perfect coverage to every seat. That said, sound reinforcement, coverage and dispersion have come a long way since I started seeing shows 30 years ago. Recently I’ve heard a lot of talk about the idea of “democracy for listeners.” I heard it in Germany earlier this year while visiting d&b audiotechnik, and I’ve heard the phrase during AES sessions. The idea is that we should strive to provide a consistent experience from the first seat to the last seat, even if we know that perfectly consistent coverage is scarcely achievable.

You could spend your entire life in the pursuit of great coverage for your church, but if your existing speakers don’t cover, well, they don’t cover. The first step in getting great coverage is evaluating your current system. Personally I find this is best done with listening test that consists of pink noise followed by some music. Pink noise is really useful in this situation, because it’s easy to hear when you fall out of the coverage of your high drivers. Most rooms that suffer from poor coverage have problems with mid and high frequency coverage more than lows and subs. And let’s be realistic, in a church environment where speech intelligibility is of paramount importance, the mid and high frequency coverage is our number one priority.

If sound system is stereo, try simply playing pink noise through only one side. Walk the expected coverage area of that side of the P.A., and listen closely for any change in HF response. If you hear high and mid frequencies fall off at any point within the coverage area, you’ve got a problem that needs to be addressed. Before jumping to conclusions about needing a new speaker system, think critically about how your system is aimed. It’s tough to get into specifics here because every system is different, but poor speaker aiming has been the culprit in a number of projects I’ve been involved with. It’s amazing what some aiming changes can do for a system that isn’t covering correctly. A few degrees of adjustment can go a long way to improving your system’s coverage.

Although it seems completely counterintuitive, the worst coverage can actually be in the front few rows, dead center and closest to your stage. These seats often suffer from being outside of the horizontal coverage of the mains, especially if your stage is wide and the P.A. is split on either side of the stage. These seats tend to sound dull, and intelligibility can suffer as a result. A dramatic improvement is easy to achieve with a set of front fills, even on a modest budget. Figuring out how many front fills you need and where to place them is outside of the scope of this article, but make sure you’ve got a console bus to feed them, and some sort of a processor to delay and EQ them. Even a small powered speaker (think QSC K8.2) with some built-in EQ presets and integrated delay can do the job. When you set up your front fills, blend them in with the main P.A. so they are transparent. If they are too loud, they’ll actually distract and annoy listeners in the front few rows.

Getting great coverage starts with speakers that have adequate horizontal dispersion for your room, but it doesn’t stop there. Coverage is also about SPL. If your speakers aren’t powerful enough to provide adequate SPLs from the front to the back of your room, the farthest listeners will suffer. Rooms like this often suffer from “rip your head off in the front row” syndrome, where the engineer pushes the speakers too hard in order to make it loud enough in the back, which results in the system being too loud in the front, or even worse, results in clipping and distortion of the amplifiers. If your system isn’t loud enough in the back, you’ve got a few options. First, you could opt for an entirely new system that’s powerful enough to achieve the proper SPL, but again, don’t brutalize your close-in listeners. A second choice is adding some delays farther back to increase the SPL for the distant listeners.

In most churches with modest budgets, delays are a most cost-effective answer. If you’re considering adding delays, make sure you’ve got a few things covered in order to do so. First, it’s preferable to have a separate console bus devoted to delays. This could be a matrix, a mono bus, or even an aux if absolutely necessary. Feeding delays from a separate bus provides the engineers with level, mute and processing control over the delays, without them needing to get their hands in the loudspeaker processor. Speaking of the loudspeaker processor, if you are adding delays you’ll likely need some sort of processor to handle level balancing, EQ and time alignment of your delays. While these functions can be done in the console, it’s always preferable to get them off of the console into a lockable processor where only a limited subset of users have access. For example, you don’t want the time alignment and EQ of your delays subjected to show file changes on the console.

Finally, there are many more advanced tools available these days for achieving great, consistent coverage across your listening area, especially in the vertical plane. Tools such as L-Acoustics’ Array Morphing, d&b Array Processing, and the use of FIR filtering can shape the response of arrays in ways that could have only been dreamed of a decade ago. Still, there is no substitute for choosing the right speakers, aiming them properly, and choosing the right fills for your room geometry. Everything else is just icing on the cake.

Vince Lepore is the director of event technical operations at Full Sail University. Contact him at vlepore@fohonline.com.