Page 34 - Fall2021

ROOM ACOUSTICS DESIGN OF WORSHIP SPACES
Acoustical Design Strategies
Adjustable Reverberation Time
In a traditional room acoustics design context, the chal- lenge of balancing support for the spoken word versus music is one of choosing the appropriate compromise between a room whose reverberation time is too long for good speech intelligibility and a room whose reverbera- tion time is too short to enhance the music. Some modern concert halls have adjustable acoustics curtains, banners, or panels that allow the reverberation time to be adjusted depending on the music to be played at that performance.
However, even if these elements were to be incorporated into a worship space, it is not practical to adjust them during the worship service, for example, extending curtains for the sermon and retracting them for the music. There are some worship spaces, however, that do incorporate adjustable acoustics curtains and panels. One example is the Roseville Lutheran Church in Roseville, Minnesota (Figure 2). Adjust- able elements were incorporated because this church has both traditional (choir and pipe organ) worship services as well as a contemporary worship service with a “praise band.”
This church knew from experience, before embarking on the design of a new worship space, that there were some very significant challenges involved in support- ing both a traditional service with choir and organ and a contemporary service with an amplified praise band with keyboards, electric guitars, amplified vocalists, and
more. My acoustics consulting firm, Acoustic Distinc- tions, worked collaboratively with the architects from the outset to develop a new worship space design that incor- porated adjustable acoustics elements, including hinged panels that could easily be opened or closed between ser- vices and a large volume above the ceiling and below the roof with a large opening over the location occupied by the pipe organ and the choir. There are large, motorized curtains in this volume that can be extended or retracted.
Use of Partially Coupled Reverberation Chambers
A partially coupled reverberation chamber is a large, very reverberant space (a space with all very reflective finishes, such as a shower stall) that is physically connected to another large space (typically, the seating area of a con- cert hall, theater, or worship space). The concept of the partially coupled reverberation chamber is to efficiently increase the reverberation time of the primary space. For example, rather than increase the ceiling height within a space to get more volume (volume is directly correlated with reverberation time), acoustically coupling the space to an adjacent volume (perhaps above the ceiling) and using that additional volume as a reverberation chamber can increase the reverberation time of the primary space with less total volume than would be required using just a single architectural volume. The effect of these reverbera- tion chambers can be minimized by providing adjustable sound absorption in the chamber. A coupled reverbera- tion chamber is a cost-effective way to achieve an acoustic goal that might otherwise be impossible because there
are usually limits to the size a building can be made due to budgetary or other constraints.
The use of partially coupled reverberation chambers is an acoustical design technique pioneered to a large extent by Russell Johnson (see bit.ly/3cE2Ir3). This technique was first developed to solve the acoustical design chal- lenge of multipurpose halls used both as theaters and concert halls. The volume of the stagehouse below the proscenium opening but outside the orchestra shell was developed into a partially coupled reverberation chamber to enhance reverberation for music when these theaters were used as concert halls.
The acoustical design concept is to have a relatively short reverberation time to support clarity but a long audible reverberant tail that is most audible after a terminal
Figure 2. The Roseville Lutheran Church in Roseville, Minnesota, is an example of the rare worship space with adjustable acoustics. Acoustic panels behind the platform and seating areas are shown in the open (absorptive) position.
34 Acoustics Today • Fall 2021