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chord is released. Reverberation time is defined as the time for sound to decay by 60 dB. In the coupled situ- ation, greater time elapses before the sound decays to that degree, but the initial constant decay is maintained.
Partially coupled reverberation chambers have been incorporated into the acoustical design of some churches where, in general, the reverberation chamber is created by the space between the ceiling and the roof, such as in the Roseville Lutheran Church (Figure 2). The acoustical benefits of this design approach as it relates to worship spaces is that the room’s natural acoustics provide for better clarity and therefore better natural support of the spoken word. They also allow the efficient development of a very long reverberation time to support choral and organ music (longer reverberation times can be achieved with less overall volume).
One of the challenges of a reverberation chamber is making sure that enough sound energy gets into the chamber to have an audible impact. When the reverberation cham- ber is formed by the lower section of the stage house in a multipurpose auditorium, it is easy to get enough energy into that chamber due to its proximity to the performance platform. Similarly, at the Roseville Lutheran Church, the pipe organ and choral loft were located directly below a large opening into the reverberation chamber.
The Perimeter Church north of Atlanta, Georgia, is another example of a worship space where the void between the ceiling and the roof was utilized as a rever- beration chamber (Figure 3). Unlike most churches, the Perimeter Church built a theater with a fully rigged stage house to support their large-scale dramatic productions; therefore, there is not much, if any, acoustical connection between the stage, where the sound originates, and the ceiling void over the audience seating area. The ceiling has discrete openings that allow the reverberant energy in this void/reverberation chamber to add to the audible reverberant tail as heard by the congregation, similar to the effect that reverberation chambers have in multipur- pose performance spaces and concert halls. The challenge at the Perimeter Church was to get sufficient sound energy from the stage up into this void, which was solved with a simple sound reinforcement system. Microphones placed over the musicians amplify their signal, which is
then played into a series of loudspeakers located above the ceiling void.
Sound Reinforcement Systems
The advent of electronic sound reinforcement systems has helped to increase intelligibility of the spoken word, particu- larly in larger and more reverberant spaces. Large cathedrals are spaces where, historically, the spoken word was not intel- ligible other than to perhaps a small congregation located close to the pastor. Understanding the spoken word has gen- erally become a higher priority in both Christian services and Jewish services. Furthermore, sermons have grown in significance and have become a more important, if not the most important, element of a service.
Most of these large cathedrals, many of which were con- structed several hundred years ago, have added sound reinforcement systems in more recent years; Notre Dame in Paris, France, is one example. This has allowed larger congregations who may gather in these spaces for special events to all hear and understand the spoken word.
Before the development of electronic sound reinforce- ment systems, attempts were made to improve the intelligibility of the spoken word through the use of sound-absorbing finishes. There are many examples
Figure 3. Recesses in the ceiling of the Perimeter Church north of Atlanta, Georgia, are actually “windows” coupling the main sanctuary volume with a reverberation chamber between the ceiling and the roof.
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