Audio Systems
You can have good acoustics without good audio, but you can’t have good audio without good acoustics. Sound systems, if applied properly, can greatly improve the worship experience and dynamics of a service.

However, sound systems serve to increase the acoustic energy applied to the room, which can enhance the poor acoustic properties of any space. Up until the early 20th century, the construction of the sanctuary dictated the style of music and speech, or at least complemented it. Organ music and choral signing are enhanced by the strong reverberation found in many classical cathedrals. The canting of monks and slow, deliberate speech of ministers were necessary elements to communicate to the congregations in these spaces.

Sound systems have given us a much broader range of speech, music and theatrical capability in the modern sanctuary. To some extent, construction styles also offer more flexibility for worship. It is essential to understand that an excellent sound system can perform poorly in a poor acoustical space. Also, the acoustical characteristics of a space can dictate the design of the sound system itself. Just as there is no “perfect” acoustic space, there is no “perfect” sound system in every situation.

Pastors, ministers, laymen and others must understand that each person perceives sound differently on both a physical and psychological level. Our ears are subject to aging and damage just like any other sensitive part of the body. As we get older, we become less sensitive to low and high frequencies in general. Overexposure to loud noises will also cause permanent hearing loss. 

The stigma many people feel against hearing aids is really tragic, as these devices can slow the hearing loss process and greatly improve one’s quality of life. That is why I’m such a big fan for assistive listening systems in churches. The quantity of sanctuaries with worshipers who will benefit from assistive listening devices is very likely near 100 percent. For many people, hearing aids will suffice, but a direct feed of the sound system brought to the ear avoids the lowered intelligibility caused by room interaction or background noise.

Reverberation
The perception of sound is very subjective. Luckily, researchers over the years have quantified some of the properties that support “good acoustics” in various situations.
 
The most common metric and problem area for sanctuaries is reverberation time. The RT60 is a measurement of the amount of time a sound takes to decay 60 decibels in a space at a given frequency, measured in seconds. Usually measured at 1000 Hz, the RT60 of a small, highly absorptive or “dead” chapel-sized room might be 1.0 seconds or less; in a large, gothic, reflective cathedral, it might be 5.0 seconds or higher. 

Predicting the RT60 in any space is a straightforward process if the construction materials and general room shaping are known. Measuring the RT60 in an existing facility is also easily accomplished by a trained acoustician with the right tools. Knowing the reverberation time in the sanctuary will give the designer an idea of what works well in the space, and what does not.
 
In general, high reverberation times are desirable for classical organ music, and, on the other end, low RT60 times are great for the spoken word. Orchestral, light background and contemporary music, as well as various types of singing, fall in between these two extremes. Therefore, the optimum RT60 will vary with the priority of the activities within the space. For this reason, many concert halls incorporate variable acoustics, which allow the reverberation time and other acoustical properties of the room to be changed at will. Similarly, new systems are available to electronically inject additional reverberation into a space - popular with organists and other musicians.

The application of highly absorptive finishes will reduce the room’s reverberation time. Common materials include acoustical ceiling tile, fabric-wrapped fiberglass core acoustical wall panels and ceiling baffles, carpet and upholstered seating or pews. People are good absorbers as well. Highly reflective surfaces will create longer reverberation times. Surfaces such as wood, plaster and painted concrete are typically very reflective. 
Any surface can be classified by an absorption coefficient, which can be measured under controlled conditions. A coefficient of zero would be perfectly reflective; one would be theoretically perfectly absorptive. Many surfaces such as light drapery and fabric banners are not very absorptive and are often misapplied in churches. The construction and materials used in the absorber make a great difference on the way the panel absorbs frequencies across the human hearing range. Typically, high frequencies are easiest to absorb, and low frequencies are more difficult to control and absorb. This is especially true when the shape of the sanctuary supports “room modes,” which are standing waves caused by simple ratios of floor/wall/ceiling dimensions. 

Reflection
In many cases, the room acoustics are aided by well-placed reflective zones. An obvious example of this is an orchestra shell on a performing arts center stage. The shell serves to naturally project acoustic music into the audience area and help musicians on-stage hear one another.

Basic auditorium design usually balances the needs of room layout and seating with proper room shaping to support the aural functions in the space. Small to mid-sized auditoriums are often designed to eliminate the need for electronic speech reinforcement altogether, but this is not common in churches. Most sanctuaries have fairly high ceiling heights and require some form of electronic speech and program audio amplification due to the volume of the space.

The addition of splayed side walls and ceiling reflectors over the pulpit and chancel areas can significantly improve a room’s acoustical performance. Essentially, these acoustician-designed elements guide early sound reflections into the audience area, providing useful room feedback to patrons’ ears. Splayed sidewalls often prevent excessive sound energy from traveling unhindered to the rear wall. Sound that travels long distances, usually front to back, will cause harsh reflections that are very detrimental to speech and music. This is because the reflected echo is delayed significantly from the direct sound that reaches the ear, causing “muddiness” of the sound and lowered speech intelligibility. 

In almost every case, the sound emanating from the instrument or speaker’s voice will reach the audience’s ears in a direct line of sight before any reflected room sound or electronically recreated sound does. The amplitude of the reflected sound waves is very important, as very loud reflections can cause the listener discomfort. For this reason, if absorption is needed to lower a room’s reverberation time, common practice dictates more absorption in the rear of the space (where sound reflections cause the most damage) and more reflection around the performers on stage or up front.
 
Reflective panels can be ordered custom-made or pre-manufactured in a variety of materials, finishes and sizes. For many situations, reflectors can be constructed on-site of common building materials such as paint-grade plywood.

Diffusion
The physics behind diffusion gets complicated quickly, but just as every finish material has an absorption coefficient, so it also has a diffusion or scattering coefficient. (Note that the scattering coefficient is a newer and different metric.) A higher diffusion coefficient for a material allows a “softer” reflection of the sound that is generally much more pleasing, especially when the listener is seated near the surface or in a focal point of specular reflections. 

Walls and ceilings can be designed to have increased diffusive characteristics, but, in general, the complex nature of diffusion calls for purchasing pre-manufactured panels from specialty acoustical product vendors. Diffusion panels range from the relatively cheap to very expensive for wood finishes and reflect incident sound across one or two dimensions. Simple diffusive panels are usually found in rehearsal spaces and some medium-sized auditoria.
 
Complex panels are common for worship facilities, especially those geared toward higher-energy music as found in contemporary worship. These panels can provide significant acoustical improvements to rooms that otherwise cannot address problem reflections by changing the physical shape of the room.

Noise Control
A final element in good acoustical performance can be measured by what should be missing: noise. Noise can come from anywhere, but common sources in churches are HVAC system supply and return ductwork (air noise), vibration from mechanical equipment like roof-top units, plumbing noise from bathrooms (rushing water) and footfall traffic from lobbies and narthex areas. Wall and ceiling constructions are often inadequate at preventing outside noise from transmitting into the room. Noise from traffic, airplanes and other environmental sources outside the control of the church can only be mitigated with good acoustical design and construction.
Assembly and performance spaces like sanctuaries require very low ambient, or background, noise levels. The most common way of classifying ambient noise levels are the NC and RC curves, called Noise Criteria and Room Criteria, respectively. Typically, the acoustician and mechanical engineer have the most responsibility for ensuring low ambient noise levels, but architects must pay attention to adjacencies that can transfer noise into the space. It is good practice to place bathrooms and mechanical rooms away from performance spaces and chapels and to include buffer areas in between.

Background noise can be thought of like a rodent infestation. Once it happens, the problems are usually difficult to address and remove. Noise control must be dealt with during the design phase of new constructions and renovations or else the consequences will be painful and expensive to resolve. There are numerous facets beyond the scope of this article to ensuring low noise in a facility that an experienced acoustician will address.
Keeping mechanical equipment maintained, tracking down noise sources and adjusting HVAC ductwork can help keep ambient noise levels down.

Conclusion
I hope that this article has given you an understanding of what can be done to improve sanctuary acoustics. Seeking out the expertise of an acoustical consultant is advised in most cases, and often the consultant can recommend the best value solution for your special needs. Acoustics is a very specialized practice. The physics of sound is at the root of all good audio design. In the real world, many audio designers know the electronic part of electro-acoustic systems well, but are not skilled in the science and engineering of room acoustics. Organizations like the Acoustical Society of America and the Audio Engineering Society continue to promote research and best practices for the professional engineering of acoustics and sound.

Brian Patrick, CTS-D, is a senior consultant with The Sextant Group, Inc.