While the Gothic cathedrals of old were designed to inspire with their heavenward soaring vaults and intricate stained glass, they may leave something to be desired in terms of acoustic performance, when used for a modern liturgy. Churches face a number of unique acoustical challenges, which call for wise, deliberate control of spatial configurations and construction assembly attributes coupled with audio/visual system engineering.
Two major concerns in acoustical design are acoustical separation, which is concerned with the transmission of sound to nearby spaces, and acoustic optimization which deals with how sound behaves within a given space.
Challenges
The sanctuary worship space is where acoustical issues can be most critical, though other spaces can benefit from acoustical consideration. Typically, a sanctuary is a large volume space with a high ceiling, which is prone to long reverberation times and the potential for undesirable sound wave interference like echoes and acoustical peaks or nulls. A reverberation time longer than 2 seconds can be attractive for music, but it can make speech muddy and less intelligible.
Room acoustics can vary with levels of occupancy. It is preferable to provide soft, absorptive surfaces in congregational seating areas such as fabric-covered foam seats and carpeted floors so that these areas have similar acoustical properties whether occupied or unoccupied, because a person’s clothed body is a great sound absorber. For example, if hardwood pews and concrete floors are used in these areas, unoccupied seating areas will add reflected sounds into the interior environment.
Sources of unwanted noise can also be challenges, such as fan and wind noise from the HVAC system, which can transmit an undesirable ’rumble’ if not adequately isolated from the space. There are several HVAC system design and control mechanisms that can considerably reduce HVAC system noise and vibration.
Constructive Interference is another unwelcome acoustical behavior where parallel walls develop standing acoustic waves of particular frequencies which reinforce each other to create an unpleasant ‘loudness’ within a particular portion of the frequency range. Minimizing and avoiding parallel surfaces can help eliminate such issues.
On the stage or platform area, acoustical conditions can help musicians to hear each other and engage with the congregation. A choir or stringed instrument group might need more controlled reflective surfaces around them than a stage for a modern praise band area.
In the congregational seating area, some congregations desire to have the joy of singing together and hearing one another, rather than feeling a sense of ‘singing alone’. Therefore, the proper balancing, angle and location of reflective and absorptive surfaces can help keep participants fully-engaged.
Every church has its own personality. Some churches prefer to have the entire auditorium be as absorbent as possible, treating it like a recording studio. Leader microphones, instruments and even microphones placed over the congregation are all fed as “dry” as possible into the sound mixing station. Then volume, delay and reverb are added “to taste” and directed to specifically time-aligned loudspeaker locations in the auditorium to create an “artificially-produced” acoustical quality for the room as selected by the sound engineers. This approach can provide various acoustical qualities to the room for different events, or even various portions of a worship service.
Other spaces, such as foyers, fellowship halls and classrooms, can face similar acoustical issues, where the balance, angle and location of reflective and absorptive surfaces need to be thoughtfully-considered. Poor acoustical performance can lead to environments where normal social conversation becomes difficult as people try to talk at higher and higher volume in order to be heard by one another as the overall volume of ‘conversation’ in the room increases.
A Cry Room is a valued amenity, allowing a parent to take their child out of the service temporarily, while still feeling like a participant in the service. One common approach placed the Cry Room adjacent to the sanctuary with reasonable sight lines, requiring its walls, window, and door to be rated and installed for sound isolation from the Sanctuary. More recently, Cry Rooms are often connected by strictly audio-visual means, reducing some of the sound isolation concerns. The A/V system must deliver the audio/visual experience of the main sanctuary into this much smaller room. Rooms for private consultation and prayer rooms also call for careful sound isolation.
Methods of Controlling Sound
There are many passive approaches that affect the behavior of sound within a space. One thing to consider is the room shape, as the angles of acoustically reflective walls, ceiling, and even the floor will affect the direction of sound waves. Walls that are parallel across the room from each other can lead to interference that creates acoustically “hot” and “cold” zones, or lengthened reverberation time. A ceiling can be angled to help direct sound towards the rear of a large seating area, or where sound reflections are not desired, absorptive materials can be employed. It should be noted that audience sight lines to speakers and performers are also direct sound paths.
Acoustically-absorptive materials can come in many forms, often as panels added in front of hard surfaces. Wall panels typically are frames with about 2″ of insulation and a fabric facing, and are only able to absorb mid to high frequencies.
Acoustical “clouds” can be added to ceilings, suspended below the main ceiling as a feature that may include reflective and/or absorptive materials. Clouds are beneficial where the ceiling height and/or reflectivity of the ceiling surface is not ideal for the acoustic qualities desired in the room.
Other opportunities to absorb sound can be found in the room’s finishes and furnishings. Carpet instead of a hard flooring option can have a marked impact, as will upholstered seats rather than pews with hard surfaces. These ‘soft’ treatments of surface areas occupied by humans also have the advantage of making the room’s acoustical qualities similar whether lightly or highly-occupied. Textured finishes, rather than smooth ones, can provide more diffuse reflections even on a hard surface. Curtains can be hung in strategic locations.
For lower frequency sounds, “bass traps” can be designed, since the relatively thinner insulation of an acoustic panel may do little to affect bass resonance. Bass tends to build up noticeably in the corners of a space, especially at the rear, and can amplify across the longest dimensions of a room (if reflected by parallel walls). The bass traps are thus most often located at the rear corners of the sanctuary. A bass trap employs an insulation such as fiberglass or mineral wool, with greater thicknesses, or even multiple layers, for a broadband capture. If there is a particular frequency that is problematic in a space, then a tuned or resonant trap can be designed that reacts to a narrow frequency range, such as a Helmholtz Resonator.
To preclude the problem of HVAC rumble, the equipment should be located away from the sanctuary walls and isolated from the structure, using rubber mounts, and it can be fitted with a silencer as well. Both supply and return air ducts can be lined with insulation. To further reduce noise, the air path along ducts can be treated as a “sound maze” with additional bends or corners, or even baffles that interrupt the flow, though this can cause the equipment to need to work harder. The HVAC equipment can also be designed for lower air speed through ducts.
There are active approaches to acoustical optimization, relying on features of a well-engineered audio/visual system. Auxiliary speakers can be carefully located to amplify the natural sound, with precise phase/time alignment to agree with the sound travel distance from the stage. Wireless microphones are affordable enough that they can be assigned to all who take the stage. However, a church should be aware of what a reliance on such methods can mean, as they may discourage ad-hoc participation such as hearing prayer requests voiced by the congregation, or other similar behavior that might be part of the church’s unique congregational style.
Acoustical Achievements at Hope Church
Childress & Cunningham took sound control considerations as integral to the design of two of the major spaces in the expansion and renovation of Hope Church. The new sanctuary addition (the Gathering) is designed as an effective auditorium, and the renovated social hub and lobby (the Commons) now plays multiple roles in the life of the church.
The Sanctuary Auditorium
The Church described multiple goals for the performance of their new Gathering space. First, the church leadership wanted to emphasize the experiential aspects of the collective. Congregants meet in person to see each other’s faces, to hear each other’s voices, and to interact directly with the worship leaders, speakers and teachers on the platform. The room must reinforce the congregational experience.
Acoustically, several things had to be addressed:
Controlling Direct Early Sound Reflections
Sound travels not only directly from the stage source to the congregant, but also bounces off other surfaces, reflected to the listener at each seat. By carefully controlling the height and angle of the ceiling plane, especially near the rear of the auditorium at increasing distances from the stage, we were able to regulate the total distance of travel by sound waves providing direct early sound reflections to congregant seating areas. It was our desire to give as many congregants as possible the opportunity to hear these audible reflections within a particular time delay range, where the ‘alive sensation’ of being in-person in a ‘live venue’ can be heard without ‘annoying echo’.
In this design, increasing ceiling heights above the seating areas closer to the stage bring direct early reflections to the front seating areas which are slightly later, and slightly softer than those in the back, but still within a short enough time delay from the sound traveling direct to congregants’ ears that it does not give the impression of an echo. This approach also provides a more uniform volume across the room, as the volume of the sound traveling from the loudspeakers reduces at travels from over the front of the stage toward the rear of the room.
While lower ceilings might help with sound reflections in the furthest parts of the space, the ceiling heights in any given worship space may be decided based on factors other than acoustical reasons. Visual and spiritual aspirations may call for a tall space wherein longer sound reflections must be considered in the overall design.
Avoiding Unwanted Audible Standing Wave Reinforcement
Another early decision was the elimination of parallel surfaces that could reflect sound back and forth between themselves. Where two parallel surfaces exist, and a full spectrum of sound is introduced into the space, it is possible for sound waves to constructively interfere with their own reflections. This can allow certain resonant frequencies to become louder than others, creating what people describe as a ‘muddiness’, ‘heaviness’ or ‘boominess’ to the room depending on the frequencies reinforced.
In the design of the Gathering, the floor is sloped and splayed primarily to improve sight-lines and focus the seat angles toward the center of the stage. The ceiling is sculpted with angles to bring the highest areas up over the center, with decorative trusses vaulting toward the front of the room in view above the stage. Even though the front wall of the stage is fairly flat, the rear wall opposing it is angled so that the walls are not parallel. Angled walls flank the stage at the front of the room, with angled extensions stretching back along the side wall toward large windows which are also set in gentle ‘zigzag’ recesses at alternating angles, before the side walls pivot back to connect to the angled rear walls.
Controlling Total Reverberation and Sound Volume Decay
Properly placed ‘bass traps’ improve the acoustics of the room by reducing bass build-up, tightening the low-end response, and providing a more balanced sound across the frequency spectrum. Four of these features were incorporated into the rear corners of the room. Large panels of acoustically-transparent fabric serve as the visual wall surface, with varying depths of free air area bounded by layered densities of fiberglass insulation. The same acoustically-transparent fabric was also employed to hide the subwoofers under the stage for a clean, tailored look.
For further sound dampening, fixed, padded upholstered seats were used in the auditorium-style seating, which cover much of the floor area. Other floor areas of the spaces were carpeted, including aisles, stairs and the stage. The seats are generally designed to mimic the sound-absorbent qualities which a clothed person possesses. Therefore, the sound qualities of the room will stay fairly equivalent whether the seats are 50% occupied or 100% occupied.
The sanctuary accommodates about 850 people, utilizing a state-of-the-art sound system. Two ceiling-mounted linear vertical speaker arrays with scaled subwoofer groups comprise the system – smaller units are ceiling-hung, and larger units are concealed under the stage. The resulting sonic qualities of the Gathering addition have proven to be a valuable asset to the immersive nature of the worship services.
The most notable qualities of the auditorium are:
• enough reflectivity that the congregation can hear themselves sing together and enjoy the qualities of ‘aliveness’ in the music
• enough reverberant decay for clear ‘un-muddied’ music, and superior intelligibility of the pastor/speaker, even for those with hearing difficulties.
The Commons
The new Commons area was designed with acoustic qualities in mind, especially since it is envisioned as a multi-use space. It has become the church’s new main lobby for support of the new Gathering auditorium, but can also be set up to host events, such as wedding receptions, dining events, and conferences, which are uses that benefit from the carefully prepared audio landscape.
The Commons is a large central area with high ceilings and hard surfaces including a polished concrete floor in this former sanctuary space. Surrounding this space on two levels are large classrooms, conference rooms, meeting room, a prayer room, coffee and kitchenette spaces, a video room, and restrooms, and other support spaces requiring acoustic isolation to allow for simultaneous use. Some rooms, such as the prayer room and video room, need to be separated from noisy spaces, so that they remain quiet. Other rooms can generate sounds that need to be contained, such as in the restrooms.
With this Commons capable of being occupied by up to 800 people as a lobby or event venue, specific design choices were made to control the acoustical resonance of the large open space surrounded by hard surfaces. Thoughtful design of the new classrooms, mezzanine and support spaces surrounding the multi-purpose Commons took plenty of opportunities to meet the acoustic challenges.
The new walls inserted to contain the surrounding functions were built at angles bending along the central open space, with relatively few surfaces parallel to another across the space. Large areas of absorptive materials were employed in the room, even though the majority of these materials are hidden from view. Inset panels create decorative niches aligned above classroom entries, creating a cohesive rhythm and adding emphasis while affording an opportunity for more acoustic absorption.
Decorative clouds were suspended below the main ceiling, hanging over the large central area of the Commons. The clouds not only help to visually define the space, but also hide more horizontal surfaces above them which were layered with additional inexpensive sound absorbing material. And, perhaps most importantly, the structures containing classrooms, etc. were stopped short of the underside of the existing ceiling, allowing for large horizontal expanses of sound absorbing material to be placed ‘on the rooftops’ of these rooms, exposing inexpensive absorptive materials to the central volume, but not to the observer’s eye.
All of these measures help to make the Commons a social hub with well-managed acoustic design responses working behind the scenes to allow education, meetings, presentations and quiet prayer to all occur seamlessly as the church needs.
Whether actively augmenting worship performance or subtly aiding to make social gatherings more enjoyable, Childress & Cunningham knows how to enliven interaction in a church community with acoustical performance that reaches beyond the obvious.
