Room Acoustics and Worship Space Design
By: Matt Swysgood
The acoustic design for a worship facility is complex and varies greatly depending on the priorities established for the space. Is the clarity and intelligibility of the spoken word the priority as it would be in a lecture hall? Are the room acoustics for the choir and the music program top priority as in a performing arts hall? Is recording or broadcasting in the mix? What are the seating requirements, and how does this affect the size and shape of the room? Unfortunately, there is not a cookie-cutter room acoustics design that fits all worship facilities. On the contrary, the huge variety of building shapes and sizes that are utilized for houses of worship make the acoustical design especially challenging. Secondly, the desired acoustics varies greatly for different styles of worship.
Imagine a cathedral, a room with great cubic volume where the reverberation level of sound is very high. Reverberation is the continuation of sound that we hear as it reflects off of the interior surfaces in a room. The distance traveled, directionality, and intensity of these reflections control the "room acoustics." In a cathedral, the highly reverberant space creates desirable acoustics for the pipe organ. You are enveloped in sound reflecting from many surfaces that arrives at your ear at different times. The clarity of the spoken word suffers in a typical cathedral, but the music and reverberant sound created by the pipe organ and the room can be fabulous.
Conversely, a smaller, more intimate space provides clarity of speech that is not possible in an immense cathedral with hard, sound reflective surfaces. Imagine a smaller shoebox-shaped sanctuary where the seats are all relatively close to the pulpit. The very different acoustics in these two examples is largely a result of the different volumes of the rooms and the distance that sound travels before reflecting off of the interior surfaces. In addition, the materials used to construct and finish the floor, walls, ceiling, windows, curtains, seats, and the like will control how sound behaves in a space. Even the people in the room add sound absorption and reduce reverberation.
Reverb Time (T60) is an acoustical measurement for the reverberation level in a room. Specifically, the T60 is a measurement of the time it takes for a loud sound in a room; imagine a loud hand clap or a balloon burst to drop 60 decibels. There is a wide range of recommended Reverb Times for various types of rooms and for a variety of worship spaces from small churches to huge cathedrals. The Reverb Time in a room can also be calculated during design by inputting room size and the various surface materials. Wood floors, painted masonry, glass, and drywall are sound reflective. Carpet and curtains absorb higher frequency sound.
Acoustical panels can absorb broad frequency sound reducing the intensity of sound reflections. Acoustical diffusers or other irregularly shaped sound reflective (hard) surfaces scatter sound with minimal loss of intensity. Overhead acoustical reflectors can be used to direct and scatter sound and improve the timing of sound reflections into a seating area. In addition to controlling sound with the room size and shape, properly applied finish materials will improve the room acoustics.
Comparing the design of a worship space to that of an auditorium, there are many design criteria to be considered. It is very important to evaluate the acoustics of the space at the design stage where the size of the room, room shape, and the finish surfaces are being determined. In addition, the HVAC design needs to be evaluated for the level of background noise produced in the worship space. Higher-than-desirable background noise, often the result of improper HVAC design, will reduce speech intelligibility and hinder music quality. Where acoustic quality is not evaluated until after construction, it is often more difficult to achieve due to the limitations of a poor room design.
Worship Space Acoustical Design Tips
2. Acoustical engineering and consulting firms throughout North America have the expertise to make sure you "get it right acoustically." Whenever possible, bring a consultant on early in the design stage to work with your architect.
3. Audio/video professionals can be helpful with architectural acoustics, but, remember, their training is in A/V equipment design not architectural acoustics. Verify your consultant's experience in architectural acoustics, hopefully with similar projects.
4. Beware blaming the audio equipment for poor room acoustics and design. Conversely, installing a new audio system, when the problem is actually the room design, can be very disappointing.
5. There are often aesthetic and interior design adjustments required in order to achieve great acoustics. Maybe that beautiful domed ceiling that will focus sound into one small area is not such a good idea.
6. Acoustical interiors products, sound absorptive panels, acoustical diffuser panels, and overhead sound reflectors can greatly enhance the acoustic quality in a space. Proper selection and location of acoustical finish materials, along with a good room design, will optimize acoustic quality.
7. Too much reverberation reduces sound clarity and speech intelligibility.
8. Too little reverberation reduces the quality of music and creates an acoustically "dead" space.
9. Controlling unwanted sound reflections can be done with acoustical absorber panels, which reduce the sound intensity of the reflection, or sound diffusers, which scatter the sound.
10. Concave or inwardly curved wall or ceiling surfaces focus sound. This can be a negative if the focusing occurs at the listener level.
11. Convex or outwardly bowed surfaces scatter sound. Irregularly shaped surfaces scatter sound. This can improve acoustics in a large space by maintaining a desirable level of reverberation and sound intensity while more evenly distributing sound throughout the seating area.
12. A quiet space allows speech and music to be best heard and enjoyed. Design the HVAC system and the shell of the space to keep the background noise in the room very low.
Matt Swysgood has 16 years of experience working with architects, builders, and acoustical consultants in product applications for improving room acoustics and controlling noise. He is currently vice president of the Architectural, Interiors, and Theater Divisions of Kinetics Noise Control, www.kineticsnoise.com.