Jump into the way-back machine and rewind 1,500 years, and you would witness the early development of, breathtaking cathedrals. The ceilings were high and impressive and the RT60s (reverb times) were long (and the longer the better). Architects and builders sought to make voices and music sound big and dramatic any way they could. In the modern age, we still have places of worship with massive reverb, and we admire (and even borrow via impulse responses) that huge sound, but our goals have changed pretty drastically. For hundreds of years, we wanted all the reverb we could get, and now, we want all the control we can get — an irony that gives me a bit of a chuckle.
How Much Ambience is Appropriate?
We like reverberation in our music, but when clergy members speak, we turn it off, because it reduces speech intelligibility. And I glibly say “turn it off,” because we can do so with artificial reverb, just like turning the garden hose on or off. Not so with the natural reverb in a space. While we want (and can’t avoid) a certain amount of ambience in our space, it must be minimized so as to accomplish clear, intelligible speech when we do mute our artificial reverb.
DIY, or Enlist an Expert?
The size of a church’s physical space and its budget (which are often related) will be key determinants in the quality and quantity of acoustical constructs we’ll use. Budget will almost certainly be the singular determining factor as to whether acoustical treatment is handled in-house or farmed out to a contractor. Whether the church owns or leases space will also figure in prominently. If the decision is to go DIY, it’s still a very good idea to get guidance from the best possible sources — perhaps a professional who attends the church, or at least good solid online research. Handy volunteers could construct acoustical treatments one Saturday and install them the next. This barn-raising approach is probably for small-to-middle-sized churches only.
Measure Twice, Install Once
Accurate assessment of the space will make a difference in the outcome. Computer modeling, which relies on accurate measurement, can be good, but unless the church is blessed to have a volunteer acoustical expert available, most computer modeling is too sophisticated. If a church is going DIY, the main goal is to identify the large, hard surfaces that cause the offensive reflections, as shown in Fig. 1. Observe visually from speaker locations — any hard and mostly flat surface that can be seen from those locations will reflect sound. Greater degrees of DIY sophistication in the placement of acoustical treatments can be accomplished by ambitious personnel with some help from Google or a generous professional, but at some point, it may make more sense to hand the project off to paid professionals.
Absorption
While absorption of low frequencies (by way of bass traps) may be very important in recording studios, the reduction of higher frequency reflections (the ones most directly affecting intelligibility) is the principal goal in large spaces intended for live performance and public speech. There are exceptions, but the main focus will generally be above the woofer range. Absorption can be accomplished with readily-available materials — usually Fiberglass, rock wool, foam or heavy cloth (typically in the form of theatrical drapery). Churches that go DIY can buy prefabricated absorptive panels or construct their own. Commercially-available absorptive panels vary widely in quality, and the old aphorism that “you get what you pay for” is largely true in this case. Treatments should be chosen in a very deliberate and intentional way — make sure they will actually solve existing problems. There are packages available that include products that solve certain acoustical issues, but perhaps not the ones that have been diagnosed.
Acoustical panels can be constructed in-house, but it’s a good idea to consider economy of scale. If you only need a handful of panels, it may not make sense to develop an assembly line and build a team of volunteers. On the other end of the spectrum, if dozens or even hundreds of panels are necessary, the project may be beyond DIY scope. Once any reflective surfaces are identified, absorptive treatments can be placed on them, even in aesthetically pleasing ways. In some cases, the suspension of absorptive devices in the air or on the ceiling may be called for, but I’d strongly recommend turning to professionals in such cases. Safety is a much higher priority than acoustical improvement.
Diffusion
“Flutter” or “ping-pong” echoes result when a sound occurs between two parallel surfaces and reflects back and forth between them until it decays away. It’s never pleasant, it adds to the clarity-diminishing soup of excessive reverberation, and it’s avoided by architects and acousticians who have the luxury of purpose-designing the space. For many smaller churches, however, the space they rent was originally intended for some non-worship purpose (retail or office space, for instance), and suffers from this problem. The general purpose of diffusers is to break up and scatter reflections in a multitude of directions to help avoid flutter echo. The degree of sophistication necessary to deploy diffusion properly will usually go beyond the scope of a DIY project, and will almost certainly require bringing in professionals.
Isolation
The proper term for what most describe as “sound-proofing” is isolation. Its typical use in church is to keep annoying noises outside the sanctuary, while keeping joyful noises appropriately contained inside the sanctuary. Proper isolation techniques that employ dead air space and floating constructs are almost always accomplished during initial building construction, difficult to deploy after the fact, and hence beyond the scope of all but the best-funded, best-educated and bravest DIY practitioners.
After the Install
There’s more to intelligibility and pleasant ambience than acoustical treatments. An audio system of appropriate size must be properly installed so as to avoid direction of energy toward reflective surfaces. The system must also be properly tuned for the space to achieve the frequency response desired by the church. It’s also up to the front of house engineer to create a blend that does not counteract the aforementioned measures that were intended to clarify sound. We want to achieve the highest possible speech clarity, but we also want the music to sound nice, so it’s worth taking time to use appropriate tools to determine a proper course of action and execute it well.
John McJunkin is the chief engineer and staff producer in the studio at Grand Canyon University.
