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Easy Acoustical Fixes

John McJunkin • November 2020Sound Sanctuary • November 5, 2020

Watch out for volunteers who make a few system tweaks to “improve” performance.

Those of us involved in professional audio for houses of worship tend to be captivated by technology as a means of solving problems or improving the quality of the sound we present. We love gear, and we’ll pounce on that flashy new plug-in or gadget to accomplish our goal and will happily pay the retail price for some magical technology.

Sometimes we do need some kind of electronic magic to accomplish our goal. But often, the better (or only) solution lies in the acoustical physics of our space, rather than some device installed in our rack. If you have the blessing of sorting out all the acoustics of your space at the beginning of the process — before a service is ever held in it — you can carefully measure and align and get it right. But even if you’re not so blessed, it’s never too late. You can always make adjustments and improve the way your loudspeakers distribute the sound in your room. Let’s look at a handful of ways to make some incremental moves towards a noticeable improvement in the quality of our congregants’ experience.

‡‡         Taming Reverberation

A substantial part of the sonic problems in rooms large enough to accommodate a church service are associated with reflections and reverberation. A room would sound dull, lifeless and disorienting if it were anechoic, but it would be a cacophonous train wreck if there were hard, reflective surfaces everywhere. The solution is a compromise between those extremes. For instance, we put absorptive acoustical panels on our rear walls, but don’t cover the entire surface — instead, it’s better to space them out a bit. Leaving a bit of hard, flat, reflective wall exposed can be good. Actually, by the time our sound gets all the way back to the rear wall, it’s going to be pretty diffuse to begin with, so the reflections will also be pretty diffuse — a good thing. The closer we get to our speakers, however, the less diffuse the output, hence giving us less diffuse reflections that are more easily noted and identified by our ears as reflections. This isn’t necessarily a bad thing — reflections are cues used by our brains to identify the size of the space.

If a sound happens between two reflective surfaces that are perfectly parallel, we get a flutter echo — the waves bounce back and forth between the two surfaces until they decay away. I describe it as that “boing” echo one hears in an empty room with no furniture. It’s not musical and it’s not pleasant, so examine your space to see if any such reflective and parallel surfaces cause it. The solution is pretty simple — choose one of the surfaces and treat most or all of it with an absorptive substance of some kind. A similar issue occurs when a reflective surface causes our sound to travel in directions other than what we expect, based on the dispersion pattern of our loudspeakers. A common one is when speakers are located very close to the ceiling and the HF drivers’ dispersion is partially directed toward the ceiling. If the ceiling is reflective, that energy will bounce back down and re-combine with the direct sound from the speaker, although slightly out of time (and out of phase) — not good. This same phenomenon occurs with walls. Placing the speakers widely apart (close to walls) to get the widest possible stereo image can result in that same reflection problem. Moving speakers away from walls and ceilings can reduce this phase mess and increase the clarity of our sound. And speakers that were installed long ago can move around a bit and not be aimed as they once were. Occasionally checking to ensure they’re actually pointed correctly is a good idea.

‡‡         Stage Volume Controls

Another common acoustical issue is stage volume. Most churches rely on a combination of sound created by on-stage sources (e.g., drums and guitar amps) and audio produced by a sound reinforcement system. In many cases, our ears hear that sound twice — once directly from the instrument, and once again through the sound system. And per physics, those two iterations of the sound will not be naturally aligned in time. Unless we do something to resolve this issue, things like digital signal latency and the additional distance of our SR speakers to congregants can cause the second signal to arrive later in time. It might seem like such tiny delays are no big deal, but in fact, these shorter delays cause the most trouble. This is the stuff that creates comb filtering and phase smear. A longer delay would actually be perceived as a discrete echo by human ears — hardly desirable, yet less troublesome in a certain manner of speaking.

Since we can’t “undelay” our FOH mix, the solution here is to reduce the amount of the direct sound. This is why we see drum kits encased in Plexiglas boxes. These boxes may not completely eliminate the drums’ stage volume, but they can at least reduce it enough to help put comb filtering and phase chaos under a little more control. Same goes for guitar amplifiers. A common solution is to hide those amps away in isolation somewhere backstage. Some opt to not only move them offstage, but put them in airtight boxes with lots of absorptive material, or even leveraging the dead airspace of boxes built within boxes. This additional effort is worthwhile for another reason — it gives the FOH mixer much more control over the mix, and thwarts the efforts of “more me” guitarists who turn up their amps after sound check to ensure that the world will hear their six-string heroics.

‡‡         Time for a Reset

We mentioned how the physical positioning of speaker cabinets can “drift” in physical positioning over many years, but there’s a related issue. When a system is installed, a contractor typically shoots the room with noise and uses an RTA to tune the system within the confines of that space. Invariably, delays and EQ are applied to accomplish this tuning, and balances are struck between various speakers (e.g., between subwoofers and the rest of the system). Sometimes, overzealous team members may tweak these adjustments, thinking they’re “improving” sound quality (or maybe they just like more bass, for instance). It’s not a bad idea to ensure that the initial baseline settings dialed in by the contractor are still in place. I recommend some kind of security to lock out such “helpful” tweaks, but if there are no such safeguards, it’s almost a certainty that settings have been changed, by accident or otherwise. Take a look and make sure they are where they’re supposed to be.

As the holidays approach, and in anticipation of the large crowds to come, now is a good time to look at these few attributes of your system to ensure that the audio part of the year-end experience will be optimal. It’s also nice to start off the new year with such things bolted down, so get to it!

John McJunkin is the chief engineer and staff producer in the studio at Grand Canyon University.

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