First published in: Church Business, Vol. 5 Issue 11, November 2000,
by Virgo Publishing, Phoenix, AZ.
All of these are valid and important design considerations that need to be addressed during concept formation of the new facility. However, in this article I will focus on an even more fundamental--though often overlooked--element: acoustics.
This is not a do-it-yourself article on church acoustics. After all, you would not expect a how-to article for calculating the acceptable deflection of a pre-stressed concrete slab at a particular superimposed loading. Likewise, acoustics is an engineering science with results that can only be predicted through vigorous mathematical computation and investigation. As a skill, it requires experience and the development of reliable intuition of one of the most complex natural sciences known to modern physics. Rather, I hope to foster an appreciation and basic understanding of acoustics so that intelligent questions can be raised in the early planning stages of your new sanctuary. These are the questions that ensure the completed project is a success, not a poor compromise characterized by remedial treatment.
Very few architects are equipped with the skills to undertake even basic acoustic design, so it is usually overlooked until late in the project, or not addressed at all. In some cases, the acoustic consultant is asked to look at the completed plans and suggest some remedial modifications. An even worse and more common scenario is to hold off on acoustic consultation until after the project is completed and its design flaws have become all too evident. Ideally, an acoustic consultant should be engaged at the same time as the architect, saving redesign time and therefore money. Here are some basic acoustic parameters that need to be discussed during the initial preliminary design stage.
If the ceiling is too low, it restricts stage sound from reaching the people at the rear of the room. If too high, sound reflected from the ceiling arrives much later than the initial direct sound from the stage and affects intelligibility. Actual ratios should be an acoustically informed decision based on required seating, auditorium dimensions, shape, layout and internal angles.
One example of an acoustically sound auditorium is the Concertgebouw in Amsterdam, with a length to width to height ratio of 1.5 : 1 : 0.63. Built in 1888, critics still consider it one of the best concert halls in the world. Though not a church auditorium, the acoustic principles still apply. The ceiling in the 2,200-seat auditorium is 58 feet high. This height requirement is often difficult to explain to church building committees because many would rather look at floor area as opposed to interior volume. They often view auditorium volume as unnecessary; plus, it costs money better spent on something people can see--a visual feature. To put this issue into perspective, I often ask committees an anecdotal question: "If a blind and deaf person both attended your service on Sunday, which of them would leave with a better understanding of what the church is about?" Hearing is more important to the worship experience than seeing.
Of these, the most solid choices are fans, rectangles and modified polygons; square is acceptable if the auditorium is large enough; while cruciform and round shapes are the hardest to design for good acoustics. After all, the cruciform is actually four rooms joined together in the form of a cross, so sound from each section affects hearing in other sections. The problem with round or partially round rooms is that the walls will reflect the sound waves to focus on a particular point. This is similar to the way a semicircular reflector in a flashlight focuses light rays into a narrow beam. At the beginning, the committee must resist the temptation to depart from acoustically tried and tested shapes in search of something unique that runs the risk of favoring form over function.
These reflection calculations used to be done by building a plywood one-tenth scale model of the internal shape of the auditorium and using mirrors and light rays to see where reflected sound would concentrate. Modifications were made by adjusting wall and ceiling profiles and testing again. Today, an accurate 3-D computer model of the auditorium is constructed and ray tracing programs are run, showing the amount of direct and reflected sound for every seat in the auditorium. By adjusting interior wall and ceiling angles (and wall and ceiling materials) the level and concentrations of reflected sound versus direct sound can be determined, as well as the frequency spectrum of that sound.
RT60 is controlled by the amount of absorptive material in an auditorium. A simple example of a room with lots of absorptive material is a lounge room with plush upholstered seats, thick carpets and heavy curtains. Its opposite would be a large, tiled bathroom or changing room in a sports facility with dressing mirrors and porcelain bathroom fixtures. A loud shout in each of these rooms quickly teaches you about the basic concept of RT60 and the effect (or, conversely, lack) of absorptive materials. It should be noted that every material and item used in construction has an absorption coefficient. Pews, people, brick, and even windows absorb some sound, so they must be taken into account during RT60 computations for an auditorium.
Not only does every material have an absorption coefficient, the amount of absorption varies with the frequency of sound. Carpets, drapes and curtains absorb mostly high frequencies while wood, sheetrock panels, and thin plaster on furring strips absorb lower frequencies.
The amount of absorption in an auditorium should be fairly even throughout the frequency range to get a balanced spectrum in the RT60 although a slight bass rise is considered musical. In practice, the lower frequencies usually require the greatest design control because they are less likely to be absorbed by padded seats and carpet. Even concrete blocks absorb some sound, so the precisely calculated use of a variety of general building materials can result in excellent acoustics. Contrary to common belief, acoustic design does not mean adding padding on the back wall after a project is completed!
The optimum RT60 for an auditorium is determinable by both the room's volume and its intended use. For example, an auditorium to be used primarily for speech should have a shorter RT60 than an equivalent volume room used mainly for music. Even the particular music style and instrumentation must be taken into account when determining the optimum RT60 for an auditorium. Contemporary music requires a lot shorter RT60 value than orchestral music, traditional organ with choir requires a longer value, and acappella Gregorian chant requires one of the longest. A lot of research is required to define the optimum RT60s for a particular church auditorium because the space has to be used for a number of different functions including speech, music, drama and also audience participation during worship.
When discussing optimum RT60s, most texts on church acoustics provide three formulaic curves based on the following delineations: Roman Catholic, High Church Protestants, and Low Church Protestants. This is an antiquated concept carried over from an era when the liturgies of each particular denomination were more uniform and predictable. Such generalizations are no longer true, which means that new churches--especially evangelical churches that use contemporary forms of musical worship--do not fit into any of the categories.
Regardless of denomination, determining the optimum RT60 for any new church requires a detailed study of that particular congregation's current and future trends. At the preliminary design stage, the ministerial staff and building committee must sit down with the acoustic consultant and clearly define their ministry style and future objectives. Once this is done, the acoustic consultant can provide design specifications that will best meet the church's needs. Areas to be considered include liturgy, forms and varieties of congregational worship, different media used in presentations--contemporary band, choir and orchestra repertoire, drama, plays and musicals--and the use of multimedia technology including audio-video recording and even broadcast.
Finally, we come to the sound reinforcement system itself. While not a part of this article, the sound system is so closely linked to the acoustics of the auditorium that its design should be handled by the acoustic consultant. It should be noted that the installation of a sound system cannot fix inherent acoustic problems in an auditorium. While the sound reinforcement system does not alter the building acoustics, a good engineer will design the system taking building acoustics into account. Sound system engineering formulae include a number of acoustic parameters, but they affect the sound system design and not vice versa. So often, churches are told that specialized acoustic design is unnecessary because the sound system will "fix" any problems with the acoustics. This is inaccurate--some churches go through three or four new sound systems before they realize that the room acoustics are to blame instead. A clear orator in an acoustically well-designed auditorium should be able to address 700 people easily without the aid of any sound system. Installing a sound system does not make the acoustics of an auditorium better or worse, but it can certainly amplify any existing acoustic problems.
Needless to say, building committees should rely on expert acoustic advice in the very beginning to avoid an acoustical monstrosity. It is usually during the preliminary design stage when a project gets off-track. The final result: an auditorium (if one dare use the word) in which the congregation has to strain to hear the message--or worse, cover their ears in self-defense. Often the acoustic consultant is contacted when construction is almost finished and then asked to help fix the potential sound problems. By this stage, many of the controlling parameters are set in stone (more literally concrete), and even the best treatments will yield mediocre results.