Uniform acoustic coverage is essential in all meeting spaces, but especially critical in a house of worship. Pastors must be free to speak as they wish; loudly to emphasize a point, softly to convey a mood. Music should be clear and not overly loud in one area, nor muddy and indistinct in another. Without a well-designed sound system the results will be hit or miss. And while it's easy to be attracted to the latest digital console or an impressive line array, before petitioning the finance committee let's look at some case studies of several typical sanctuaries.
First things first
Before thinking about an equipment list, it’s essential to understand how the system will best serve the ministry. Worship styles vary from church to church. So do the shape, size, and acoustics of the sanctuary. Determine your current and future worship styles and production plans. Does your church present traditional, blended, acoustic or contemporary music styles? What about the future? Are you planning on hosting live concerts by touring bands? What about theatrical productions? Answers to these questions will dictate the correct choice of loudspeakers, and then the task becomes optimizing speaker placement, and later, optimal system tuning.
Rectangular churches
The traditional small- or mid-sized chapel is usually best served by columnar line arrays with subwoofers added, or narrow-angle point-source loudspeakers. When a room is deeper than it is wide, it’s important to keep as much energy off the side walls to avoid harmful reflections. This is especially true if the building materials include a lot of glass, brick, or stonework.
Many loudspeaker manufacturers provide modular columnar arrays that can be increased in length to tighten the vertical pattern, thereby keeping energy off the floor and ceiling. Placement is critical. Try temporary placements while listening and walking the room before affixing the columns in their final location. The goal is to make the energy as uniform as possible from the front to the rear. If the chapel has rear or side balconies, then consider adding small column arrays on delay to ensure good balcony coverage. Again, these should be positioned temporarily to determine the best location before finalizing. Tuning will require a good knowledge of how to set delay times; if the settings are not accurate the delay speakers will add aural confusion instead of improvement. Such systems can be used in stereo, but there is usually little advantage to it. Mono helps ensure all attendees will hear the same mix.
Fan-shaped churches###/SUBEAD###
There will be a break-in period in which the response changes as the cones, spiders, surrounds, and diaphragms settle-in. As time goes by, fatigue will occur that also alters the response.
In rooms that are wider than deep, it's often best to use a series of distributed loudspeakers, spaced so that each one covers a distinct area. They can be flown if the ceiling is high enough, or attached to the ceiling with brackets if the ceiling is too low for suspension. Most subwoofers are essentially non-directional, so their location is not as critical. As a rule, stereo should never be used in any room in which the width is the longest dimension, unless the system is comprised of wide-angle left and right arrays that cover all seats from the far left right to the far right. You don't want one side to hear differently than the other, but this adds the problem of significant time smear and the left and right arrays may need to be supported by a mono center cluster.
Large sanctuaries
In larger buildings, especially those with very high ceilings, a modular line array is often the best solution for even coverage because the line can be assembled to the desired length, and each module can be angled to provide the required vertical coverage while avoiding reflections from the ceiling.
Almost all line array manufacturers provide comprehensive prediction software to help the installer make the best choice in array size, shape, and placement. Most provide this as an inclusive service with the purchase.
Modules are typically available in several sizes to match room size and acoustic power. Such systems still should be “field focused,” which means relying entirely on the predictive software, but walking the room to make adjustments as needed. Line arrays are well known for throwing the sound-field long distances, but in a very large room it's likely that ancillary delay speakers may need to be added, perhaps in numerous locations, to properly cover rear seats and balconies without being too loud in the front regions. Subwoofers can usually be flown, which has the advantage of emitting the energy from one location, but if they must be ground-stacked because of space or structural limitations, that's usually sufficient but requires more attention when tuning.
Sanctuaries that seat around 800 can begin to be potential candidates for line array systems. For larger sanctuaries over 1,500 seats, a properly configured and positioned line array will more likely be the optimal solution. If the room is very wide it may require three or four hangs for sufficient horizontal coverage. Room geometry is the key. If the seating areas to the sides are much closer than to the rear, and they usually are, then an array comprised of smaller modules or point-source loudspeakers may be all that's needed for coverage.
Directional bass control
Progressive system designers are using multiple subwoofers to create cardioid arrays, instead of the omnidirectional pattern that conventional subwoofers exhibit. By putting adjacent enclosures out of phase with the in-phase enclosures, and facing them rearward, lobes can be generated that provide significant directionality even in the very-low frequencies. The full story is more complicated and may require incremental time delay expertly adjusted to achieve the desired results. Also, the cost will increase, as some of the subwoofers will be used to intentionally cancel energy from the others. That said, if the room has significant low-frequency problems, then it's certainly something to consider. And that leads us to system tuning.
Precision EQ and timing
A good sound system might provide excellent sonic quality right out of the box, especially when used outdoors where there may be fewer major reflections. In an indoor environment, however, the sound system must be integrated into the room. All rooms exhibit resonance, some of high amplitude, others not so much. The more reflective the surfaces, the greater the resonance and the longer the reverberant field. Other factors come into play such as architectural elements like arches and ceiling domes. In some cases the only real solution may be adding sound absorbers or diffusers. But in most situations the effect of the room resonance can be controlled with properly chosen, directional loudspeakers and carefully applied precision equalization. This cannot be accomplished with a 1/3-octave graphic equalizer because room resonance will not be polite enough to fall precisely on ISO band centers. A graphic chops out too much and can cause the opposite effect of reducing room resonance because it's cutting the wrong frequencies. Only a quality parametric equalizer (PEQ) will reduce the problems. Setting a parametric equalizer by ear to flatten the system is not recommended. It's almost impossible to get even close in frequency, bandwidth (Q), and amplitude without the use of high-resolution measurement equipment. It's quite unlike adjusting the PEQ on a channel strip by ear.
System tuning is a practice in itself, one that this author began some 30 years ago using expensive Hewlett-Packard analyzers. At that time I had to figure it out for myself. Fortunately, today there are far less expensive alternatives that run on laptops, and training can be arranged. The software should be based on a dual-channel FFT engine. If it can't be run in near real-time, it's not going to do much good. You have to see the effect of the changes you make while you're making them. In addition to the software, you'll need a flat mic preamp and a true measurement microphone. The cheap ones are a start, but for critical room analysis and system correction, a high-grade mic is essential.
Setting accurate delay times for ancillary speakers once required a process known as “phase unwrapping,” but is now relatively easy because most Fast Fourier Transform (FFT) software, which produces complicated mathematical calculations to create an Inverse FFT function that quickly indicates the proper time delay. Still, it takes experience and skill to know where to place the measurement mic. Unless all delay speakers are in a straight line to the stage speakers, it's important to understand basic vector geometry so that the measurements will be valid.
Lastly, if the system is new, there will be a break-in period in which the response changes as the cones, spiders, surrounds, and diaphragms settle in. As time goes by, fatigue will occur that also alters the response. How soon and how much is a function of temperature and humidity swings, and how hard the system is driven.
