Reverberation and echoes are two naturally occurring phenomena most people are familiar with, having heard them numerous times. Reverberation only occurs indoors and sounds like an indistinct sound that fades away. The sound may fade rapidly or more slowly depending on the size of the room, construction materials, and other factors. An echo sounds similar to the original sound (a hand clap, for example), and repeats a number of times as the sound reflects off of nearby surfaces. Each repetition may be very quick or very slow depending on the distance between the reflecting surface and the listener.
So, why should a pastor of a house of worship care about these two things? Because both phenomena occur in your sanctuaries, and affect the sound of your worship team and the understandability of your sermon. Rooms that have poor acoustical attributes can make it exhausting, if not impossible, to understand the Word being spoken from the pulpit. And when that happens, the effectiveness of that Word is greatly reduced.
Acousticians use traditional methods of room size, geometry, materials, and finishes to control the acoustical properties in a room. Some acoustical properties are classified as anomalies and are not desirable. Excessive reverberation and echoes are just a few of the difficulties caused by improperly designed or built rooms.
Multi-Purpose Room Acoustics
Today's church sanctuary is often used for a variety of different audio environments. At one moment, it might be supporting rock music; at another, a sermon or lecture; at a third, an orchestra or pipe organ. Each of these uses requires a room with different acoustical signatures for ideal enjoyment. Speech and amplified music want the shortest reverberation timessomewhere under 1.5 seconds; orchestral ensembles are in the middle range of times; and choirs and pipe organs like the longest times, typically above 2.5 seconds. But, you're doing all these different things in the same room. While it's possible to design a room that can be physically modified to create different reverberation times, construction costs are high and probably out of reach for most houses of worship. Also, traditional methods of variable acoustics such as movable walls, large doors, and rotating panels, provide only a limited range of variability insufficient for rooms with a wide range of reverberation needs for the various programs. So, usually, the architect and the acoustical consultant provide a suitable short time which is good for speech intelligibility and amplified programs, leaving the needs for other types of musical programs unsatisfied.
Accommodating Other Programs
However, there is another option. The possibility exists electro-acoustically (a combination of electronics and loudspeakers) to provide a much wider range of room reverberation than is possible with traditional variable acoustics. This reverberation enhancement system is another sound system that co-exists in the same room, but operates totally independently from the regular sound system. Microphones, processing, amplifiers, and loudspeakers are all separate and can be easily accommodated in renovation or new construction.
A Real Example
The Church of St. Michael and St. George in St. Louis, Missouri, is a 425-seat Episcopal church with traditional Episcopalian worship. Sermons, congregational singing with pipe organ accompaniment, choral anthems and special concerts with pipe organ accompaniment are all in occurrence. The speech and pipe organ needs for reverberation support are widely divergent, and the church's existing acoustical enhancement system had failed and was no longer in use. The sound reinforcement system was also failing. The church consulted with their local contractor and decided to use the Yamaha AFC (active field control) system to provide electro-acoustic enhancement in addition to a Yamaha and contractor designed sound reinforcement system.
The AFC system has four hanging microphones, the AFC processor and matrix, and 18 channels of amplifiers and loudspeakers installed at the direction of Yamaha acousticians from the Center for Advanced Systems Technology. The AFC system takes and expands the 1.41 second reverberation time to 2.74 seconds for the choir and pipe organ preset. The Yamaha AFC loudspeaker is a coaxial type with very low directivity to create a sound field and prevent listeners from localizing on the loudspeaker locations. The AFC system uses a simple pushbutton panel for changing presets.
By providing the ability to change the apparent acoustical properties of the sanctuary, the Church of St. Michael and St. George is able to support a wide range of musical styles while also ensuing that the sermon is heard clearly throughout the facility.