Everybody enjoys the extra dimension of hearing music in stereo. Also, everybody wants to clearly understand the words of the pastor and the worship leader-even when they are speaking softly or whispering for dramatic effect. Ideally, your church's sound system will accommodate both. Unfortunately, the two are often at odds.
Depending on a variety of factors, implementing a stereo system for music could markedly degrade spoken word intelligibility in a significant number of seats. Consequently, the decision of whether to go for stereo or stick to mono should not be taken lightly when it comes time to design and install a new loudspeaker system. The mono/stereo choice will hinge on a number of variables: room layout and dimensions, room acoustics, worship styles, visual aesthetics (which often limits loudspeaker locations), and equipment budgets. Before you begin the process, it's important to understand the acoustical principles involved, and consider the possible trade-offs. To help guide your decision, three experts in the field, introduced as we proceed, will offer their insights and advice.
ONE POINT IS BEST
For maximum spoken word intelligibility, you want the sound of the voice to arrive at the listener's ears—as much as possible—from a single loudspeaker or array. This, first and foremost, is the rule of church acoustics. Multiple arrivals, whether from different loudspeakers or room reflections, undermine our ability to pick out the consonants that make speech understandable.
“If the acoustic environment is reflective to the point that it compromises intelligibility, then mono is the best way to go,” says TC Furlong of Chicago-area systems integrator TC Furlong Inc. “The same applies if the shape of the room will not allow a significant portion of the room to be in the stereo field.”
A case in point, Furlong cites, is the complex point-source cluster he recently installed in downtown Chicago's historic Moody Church—a room with acoustics specifically designed to support a voice speaking from the pulpit.
Of course mono systems don't have to use a single cluster, simple or complex. They can employ speakers in multiple locations, either as delay and fill speakers for a main system or in a distributed system comprising multiple smaller loudspeakers. But the critical factor for maintaining optimum intelligibility is the same: design your coverage so that nearly all of the sound in any particular seating area is coming from only one source.
A well-designed mono system is not necessarily inexpensive. Yet, even in complex scenarios, the cost-for-performance ratio is reasonable—compared to stereo—because only one source is needed for each seating area.
“We recently did a system at Skyline Church in La Mesa, Calif., that was mono because of three factors: the seating configuration, desired level of performance, and available budget,” says Vance Breshears of Acoustic Dimensions' San Diego office.
STEREO: BENEFITS AND COMPROMISES
To illustrate the difference between a mono system and a true stereo system, think of a typical church with line arrays on each side of the stage. If you are designing a mono system, ideally you want each array to cover only those seats on its own side of the auditorium, minimizing any overlap in the middle. (This helps to avoid multiple arrival times that can impair intelligibility.) For truly effective stereo, in contrast, you need more powerful arrays with a much wider coverage pattern, so that the sound from each array is heard throughout the auditorium. Otherwise, the stereo effect will be limited to a small “sweet spot” in the center seating area.
Effective stereo, then, costs more and could also reduce intelligibility. But don't rule it out too early.
“Stereo can be accommodated until things get too wide,” says Bob McCarthy of Alignment and Design Inc. in St. Louis. “My first inclination is to go with stereo because the customer expects this. The trick is to confine the reach of the stereo overlap zone to only the area where stereo can be perceived, which can be quite small. That gives the experience of a wide horizontal sound filed field without the intelligibility loss that results from overreaching your coverage.”
Breshears concurs, but also brings up the trade-offs. “Stereo can work well in a relatively narrow room where the distance between the speakers is not excessive,” he says. “The disadvantage is that the full stereo effect is largely limited to the center of the room. Elsewhere, you localize to the sound that arrives first and is the loudest, from the nearest speaker.”
When full stereo coverage is restricted, as it often is, the sound mixer must be careful not to shortchange those sitting outside the “sweet spot” in the center. “I love stereo whenever the basic room dimensions allow it,” says Furlong. “But the mixer must be careful about hard-panning only selected sounds, such as keyboards, guitar effects and reverbs. Main vocals need to stay close to the center.”
The danger with stereo, as McCarthy hints previously, is not to push too hard for a full stereo effect throughout the room by overlapping too much. Although this is not a problem for stereo music, when a single voice comes through the same system, there will be significant variations in level and frequency response because of comb filtering effects generated by acoustic cancellations as the same sounds arrive from different distances. Inevitably, overall intelligibility will be hampered. If the acoustic environment is well controlled and the system itself produces highly intelligible sound, then the results still can be acceptable—although less so than with a mono system of equivalent quality.
STEREO FOR WIDER ROOMS
The wide, fan-shaped architecture of many modern church auditoriums is problematic for generating usable stereo. Even newer line arrays with the widest horizontal coverage patterns can't do the job, in part because it would mean flooding the stage with sound too. However, there is a somewhat controversial solution that may work in some scenarios: the LRLR stereo system.
With this approach, the auditorium is split into stereo zones, with additional infill (or “stinger”) speakers supplying the intermediate left and right signals to define the stereo image across the arc of seating. The extent to which this is a valid solution depends in large part on room dimensions and acoustics, and how aggressively a stereo mix is applied. According to Furlong, under the proper circumstances such a system “can be an interesting and valid compromise between stereo and mono.”
But actual implementations of such systems are rare. “We seldom employ this approach because overlapping coverage creates multiple arrivals, which is okay for some music but bad for speech and overall clarity,” observes Breshears.
McCarthy is forthright in stating reasons for his rejection of the concept. “I have never specified one of these,” he asserts, “but I have been called in to attempt tuning some after the church had struggled with intelligibility problems. There are many negatives and few positives to this approach. The visual does not line up with the audio imaging, intelligibility is compromised, level uniformity is reduced, and only a minority of listeners falls within the stereo perception window.”
LCR: BEST OF BOTH WORLDS?
One obvious—albeit expensive—solution is to design and install a stereo system for music and a mono system for speech. Someone on Broadway stumbled on this breakthrough years ago, and it is now the de facto standard for nearly all musical theater systems. The left and right loudspeakers are hung as arrays (or erected in towers) to carry the stereo music of the orchestra as well as directional sound effects; the center array is dedicated to reproducing dialog and sung vocals.
This approach generally earns favor from our experts, with a few caveats.
“For clients with a good understanding of how to mix on these systems, LCR can provide the best listening experience for the greatest number of seats,” claims Breshears. “The mono center channel provides the clarity and intelligibility while the left-right systems provide the stereo imaging. We recently installed a system at Venture Christian Church [Los Gatos, Calif.,] with a conventional center cluster and left-right line arrays.”
McCarthy is mindful that careful design and professional operation is critical to making this concept work. “An LCR system, we must remember, requires full coverage of all seats by the center system, a point that is missed far too often,” he says. “It also requires careful management of signals coming from the stage to ensure that the vocal information is isolated from signals going to the left and right channels. If not done properly, you can end up with vocal information in all channels, creating an intelligibility mess with out-of-time overlap.”
It should be noted that a full, Broadway-style LCR system requires a mixing console with true LCR panning—a feature lacking in many lower-priced mixers. LCR consoles allow each channel to be panned across all three points, from left to center to right, or anywhere in between. This is not the same as a console with both stereo and mono outputs: in this case, channels can be panned left to right, but mono output is either a separate selectable bus or simply a summing of the two stereo channels.
That said, there is no reason why churches on a budget can't use a lower-priced mixer to do a hybrid mono/stereo system. It's rare for churches to have a need for panning between center and side channels anyway. The mono center channel can be dedicated to speech and lead vocals, with those channels panned for stereo effect going to the left and right outputs. If your church has stereo music and loves it, but it struggling with intelligibility issues, installing a dedicated mono center system could prove a surprisingly cost-effective solution. The music can be wide, the message clear, and everybody can be happy.
That said, for some churches options will be limited. The grand cathedrals of Europe will be forever mono (stereo was not big in the 14th century), and churches with very wide auditoriums and tight budgets may have to accept trade-offs. For the rest of us, knowledge of basic principles combined with careful planning and budgeting will result in a loudspeaker system that makes every word crisply intelligible and envelops the congregation in spacious music.
Finally, for those seeking more technical background on the subject, I recommend a web tutorial by Barry McKinnon of McSquared System Design Group in Vancouver, British Columbia. Find it at www.mcsquared.com/mono-stereo.htm. Most informative is an interactive graphic that depicts how the various system configuration options work in a typical, fan-shaped church auditorium.
