Page 36 - Fall2021

ROOM ACOUSTICS DESIGN OF WORSHIP SPACES
Figure 4. The vaulted ceiling surfaces at the Riverside Church in New York City are Guastavino tile that required sealing after sound reinforcement was added to the sanctuary.
of churches in the United States that incorporated Guastavino tile in the form of Akoustolith (a prod- uct developed in the early 1900s expressly for the purpose of limiting undesirable reflections in spaces with vaulted ceilings), usually in the ceiling, to reduce the reverberation time. But these finishes improved one acoustic parameter at the expense of another; the acoustical quality of the spaces where they were installed declined for music and, in particular, choral and organ music, both of which are typically the pri- mary, and sometimes only, source of music in these spaces. One example is the Riverside Church in New York City (Figure 4).
As the quality of sound reinforcement systems increased, many of the churches that incorporated Guastavino tile, including the Riverside Church, have decided to go back and use multiple coats of special clear sealants to increase the reverberation to provide better acoustical support of music. However, one challenge with sound reinforcement systems is that they can increase loudness but not neces- sarily speech intelligibility.
In order to increase intelligibility, these systems must provide a significant increase in the loudness of the direct sound (the sound that travels to a congregant’s ears directly from the loudspeaker), with a smaller increase in the loudness of the reverberation. One way to do this is to provide small loudspeakers close to the congregants. These systems are known as pew-back systems. If the speaker is close to the congregant, it is easier to improve the loudness of the direct sound compared with the loud- ness of the reverberant sound. Still, pew-back systems are expensive and tend to sound unnatural, but as electronic sound reinforcement technology improves, it is becom- ing more possible to attain the elusive combination of natural sound, lower cost, and better speech intelligibility.
As sound reinforcement systems developed, many churches suspended large speakers or arrays of speakers over the platform or otherwise mounted them at a distance from the congregants. These systems often increased the level of reverberation as much as the level of direct sound; as a result, many of these attempts were not successful.
One of the most significant advances in the design of loudspeakers that is continuing to improve to this day is better directional control over a wider frequency band- width. This allows a loudspeaker to aim a larger percentage of sound energy into the sound-absorptive seating area, with a smaller percentage of sound energy going into the
Figure 5. Steerable arrays in the ceiling permit a minimal suspended speaker array system at the Church of the Resurrection in Leawood, Kansas, to serve a large congregation, aiming sound toward the absorptive seating areas and away from the reflective surfaces.
36 Acoustics Today • Fall 2021