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Improving Sound for Multi-Use Spaces

John McJunkin • September 2021Sound Sanctuary • September 10, 2021

Sometimes the multi-purpose space is also the sanctuary, such as Nashville’s St. George’s Episcopal Church, where the worship area doubles for preschool play, sports, concerts and community events. Here, a Fulcrum Acoustic FH15 system proved the ideal solution.

Picture the scene: a small-ish church has expanded up to three services on Sunday morning, and all 80 seats in the little rented space are at capacity during all three services. The time has come to move to a larger space. A search is launched, options are examined and a new place that seats 250 is secured. The congregation bids the small space adieu and volunteers move everything to the larger new space. A new and slightly larger P.A. system is acquired and deployed, and services are held in the new location.

There’s lots of excitement, but lots of comments about how the music and the pastor’s voice now sound “mushy” and “unclear.” Could it be the new P.A. system? It’s brand new — state of the art — it should sound better than the old one. But it doesn’t. An expert acoustician (a cousin of the pastor’s wife) is brought in to examine the situation. He sorts it out right away. The new room is a box. The painted drywall walls are all parallel to each other and hence very reflective. The new, larger speakers are on stands in the corners of the room on either side of the platform. And the sound is a cacophonous soup. Unfortunately, the church’s budget was largely swallowed by the move and acquisition of new technology for the new space. How do we resolve this problem?

This storyline plays out in slightly different ways all across the fruited plain. Sure — we all want larger sanctuaries and more sophisticated production, but not the difficulties that come with larger spaces and larger P.A. systems. These acoustical problems are more common among growing churches who rent space — most of the time, the spaces they rent are not developed with proper acoustics in mind — they’re frequently light industrial spaces like small warehouses, for instance. In some ways, bigger spaces are acoustically better — room modes that cause standing waves occur at increasingly higher frequencies in increasingly larger rooms. But, unfortunately some negatives come along with that increased seat count. Aside from the tendency for those spaces to be squarish and industrial in nature, the additional size requires more acoustical treatment, and that costs money. There are a few things that can be done without breaking the bank. Let’s discuss a few.

Affordable Solutions

When the question is “how do we reduce reverb and reflections,” the answer is almost always “absorption.” Indeed, larger spaces require more absorption, and it’s usually not free. But the good news is that we don’t want every hard flat surface completely covered anyway — as a little ambience can be desirable. Job number one is to walk around and examine every part of the room. Where are the big, flat, reflective surfaces? The rear wall tops the list of usual suspects, along with the side walls, the floor and the ceiling. The trick in all cases is to cover large-ish swaths of all of these surfaces with stuff that’s not very reflective.

It’s not plausible to absorb low frequencies on a large scale like this — we’d need absorptive stuff in the thickness of one quarter of the wavelength of the lowest frequency we’d want to control. So if we wanted to absorb low frequencies at 200 Hz, we’d need absorptive stuff about a foot and a half thick — not easy or cheap. In fact, unless we want absorptive stuff all over the place an inch thick or more, it’s not really plausible to absorb much below 5k Hz. The good news? We can get some control over those higher frequencies, and the result is that if we have those high “clarity” frequencies relegated to appearing only from our speakers, that helps to tidy things up.

If the floor’s not carpeted, let’s at least get some rugs going, and specifically in the places where energy will be directed by our speakers. It’s probably not plausible to cover the walls in their entirety with absorptive stuff like drapes or soft artwork or inexpensive acoustical panels, but covering some of the walls will at least reduce the reflections. And windows are very hard, very flat, and very reflective. You’ll almost certainly want to get some kind of window covering happening, and heavier drapes or curtains are the best bet here. As to walls, some reasonably priced commercial panels are available, but if you have a few handy carpenter types in your congregation, framing up some compressed Fiberglas insulation and covering the resulting panel with some attractive acoustically transparent cloth wouldn’t be difficult, and the price would be substantially less than ready-made. Heavy drapes can cover more than just windows too — this has been a staple of movie theaters since time immemorial.

It’s also smart to use soft, absorptive seating if you can. A small church I attended a while back had quite a few of the stackable variety, and they were pretty posh and cushy, which helped to make a nice difference by way of absorbing those higher frequencies. And also considering that higher frequencies are much more directional than lower frequencies, we can help ourselves by directing the energy from the speakers straight into our congregation, rather than toward the back wall. Obviously, line arrays are the best way to do this, but even point-source loudspeakers can be “aimed” down from up high. This accomplishes a couple of things: first, it helps to reduce the amount of energy pointed at the back wall to be reflected back around the room, and second, if most of the output of the speakers is directed toward our congregation, we can probably get away with lower SPLs, which also reduces the amount of reflections.

And this points to yet another thing we can do to help keep the cacophony down — literally reduce the output of the speakers. Most churches are mixing for 80-90 dB SPL at the front of house position. Reducing toward the lower end of that range (or even lower) has the effect of reducing the amount of SPL that actually strikes reflective surfaces. For what is hopefully an obvious reason, we’ll also want to direct the output of our speakers away from the walls.

Also, on the topic of congregants, there is another helpful idea that isn’t particularly obvious at first, but makes perfect sense from a physics standpoint. The human body is, in essence, a bag of water. Up to 60 percent of the human body is water, and our relatively soft skin and clothing absorb high frequencies much better than hard floors. The more people seated in the sanctuary, the more of that absorption happens. We all know this — we’ve had that experience of needing to goose the master fader a bit during services versus the level during sound check when no is in the room. So now that we have a sanctuary that seats 250 (and could accommodate those same 240 who attended our three services in the old location, 80 at a time), we may consider scaling back to two services of 120-ish each — and hopefully more now that we have a nice, shiny new location.

And Don’t Forget…

One last thing to consider aligns with my general philosophy on church sound. Try to get 100 percent of the signal through the P.A. and under the control of the FOH mixer. If we treat our room, aim the speakers correctly and get some of those reflections under control, it all goes out the window when our hotshot guitarist points his Marshall stack at the back wall and cranks it to 11. Boxy, rectangular rooms will never sound incredible without expending substantial money to make it that way, but we can noticeably improve the clarity with substantially less financial investment if we are smart about it.

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

 

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