Get the Acoustic Advantage
The best sound is built-in sound

By Michael Jarzabkowski

When I begin discussing acoustic design of churches with clients, their first thoughts often turn to visual aesthetics. Interior design items also serve an acoustic function, however. These include columns, buttresses, pilasters, cornices, soffits, profiled ceilings, ceiling beams and rafters, angled roofs, floor and seating materials, 3-D wall ornamentation, and even large statues. If acoustic design is initiated at the very start of the overall design process--along with liturgical and architectural design--the whole project will be an integral unit that is appealing to the eyes and the ears.

Preliminary design factors

The most important initial decision is the choice of sanctuary floor plan or shape. There are numerous variations, but the options generally fall into six basic categories: cruciform, rectangular, square, polygons (hexagon and octagon), fan and diamond. The chancel (stage or altar area) may be located anywhere logical within the basic shape, and combinations of shapes provide even more variations.

Wall and ceiling reflections significantly affect acoustics, so the choice of floor plan should be made in conjunction with your acoustic consultant. The more fragmented the plan, the greater the challenge to achieve acoustic uniformity. Generally, the best choices for acoustics are rectangles, fans, stretched polygons and other open, irregular shapes. Circles, ellipses or any inward curved wall surfaces are usually the most challenging. (One should note that a many-sided polygon approximates a circle; do not go beyond an octagon.)

Liturgical renewal has moved towards more open design, seating the congregation closer and spreading around the officiating area. This move has emphasized a movement to wider- and shorter-shaped floor plans from the previous long, narrow sanctuaries that distanced the congregation from the celebrant. In many cases, the rectangular shape is now used sideways, so the width is greater than the length, making ceiling reflections more significant than wall reflections. Any shape, however, needs to be carefully analyzed because wall and ceiling reflections provide the listener's spatial perception in relation to the direct sound.

Liturgical renewal has also moved balconies closer to the stage or altar area and along the parallel sides of narrow sanctuaries. Combining good acoustic design and better sight line requirements has necessitated breaking up the parallel side balconies up into angled terraces, or what is known as vineyard style balconies--collections of angled and stepped balconies that cluster around the altar area.

Although some churches reject the idea of balconies and choir lofts, these elements have been a part of traditional church design for more than 1,500 years. Even though they aid listening by bringing people closer to the pulpit or lectern--the sound source--the stairs involved are a disadvantage for churches that require worshippers go to the altar for the Eucharist.

Balcony design certainly affects acoustics; as such, layout, position and sight lines should be carefully investigated during the preliminary design stage. Everyone seated in the balconies should be able to see and hear just as clearly as those people on the main floor. The ratio of the Depth to Height of the area under the balconies is also important. Depth should be less than the Height so that those in the rear seats under the balcony will receive enough room reflections and reverberant sound to provide spatial cues (see Figure 1). Also, the soffit, or underside, of the balcony should be sloped correctly so that reflections from the stage add to direct sound in the rear seats.

Sloped floors enhance sight lines to the pulpit and altar, and provide better hearing for those at the rear of the room. They do not aid liturgical processions, however, and are not less versatile for multi-purpose use if the space doubles as a fellowship hall. As such, sloped floors are better from a purely acoustical position, but this determination will vary on a church-by-church basis.

Acoustically, sanctuary height is also important. If the ceiling is too low, sound from the pulpit area will not be reflected correctly to the rear of the room, especially in large spaces. On the other hand, a ceiling that is too high gives delayed reflections that can disturb the perception of the direct sound. The ideal ratio of Length to Width to Height looks like this: Width = 1.0; Length = 1.2 to 1.7; Height = 0.4 to 0.7 (see Figure 2).

The ideal range is given as a ratio, so the formula can be applied to a sanctuary of any size. The orientation of Length and Width is not significant, so it can be applied to situations in which a sanctuary is wider than it is long, taken from the pulpit position. The ratio has quite a range, allowing for coordination with the ceiling profile and the chosen floor plan. Acoustically, some floor plans work better than others, and ceiling or roofline angles also affect how reflections are returned to seating positions. Ceiling height needs to be investigated very early in the design process since it not only affects the acoustic outcome, but also lighting design, ventilation, heating and air conditioning and the overall project budget with proposed wall height and structural requirements.

Interior design details

The most significant interior design details are architectural ones that absorb, reflect or diffuse sound. A sanctuary should be designed to have a particular Reverberation Time, or RT60. Churches that worship with a choir and organ require a much longer RT60 than those using guitars and synthesizers, for example. All churches, however, should consider speech a priority, and this need has to be coordinated with the acoustic requirements for worship. Some spaces will host both traditional and contemporary worship, and these can be designed with acoustics that change the RT60 to some degree as well. Every church committee should ask the architect to predict the proposed sanctuary's RT60. If the answer is not given in a numerical value, then that committee and the architect might have no idea what acoustics will be like.

Two major elements that need to be chosen quite early are seating type and floor material. Hard, wooden pews absorb much less sound than do plush, fabric-covered seats with armrests. For flooring, the choice between hardwood, thin carpet without underlay, thick carpet with 1/2-inch underlay, or a combination of carpet in aisles only and wood or tile in the seating areas has a major impact on the amount of sound absorbed.

In a few special cases--a church that worships with Gregorian Chant, for example--padded pews and carpet absorb too much sound whereas wooden pews and wood or tile floors provide longer Reverberation Time. Otherwise, in most cases, nearly any seating type and floor material is acoustically acceptable. Nevertheless, an acoustic consultant needs to know early what type and material will be used so that wall and ceiling materials can be selected to adjust or compensate for the acoustic properties of each choice.

Another important part of acoustics is sound reflection and diffusion. A large, flat wall will simply reflect sound back, but a wall with a deep three-dimensional profile can diffuse sound by reflecting it in many different directions, breaking it up. Columns, buttresses and pilasters are all structural supports for a building, and if they are exposed against an interior wall, they can be a great acoustic aid for sound diffusion. Architects should not feel the need to hide these structural elements but instead dress them up as part of the interior. Large wall moldings and cornices--even window frames and ledges and cornices, if they are of sufficient scale--also diffuse sound.

The same concepts apply to the ceiling. Rather than being flat, a ceiling should feature profile angles, recesses and other dimensional facets to help diffuse sound waves. At the same time, it needs to be sloped or angled to reflect sound--ideally towards the rear part of the room--so some detailed analysis of the ceiling angle and profile is required. It should be noted that in most cases, the ceiling should be reflective material rather than absorptive. The use of lay-in acoustic panels ceiling tiles should be reserved for libraries and other quiet rooms. A room designed for worship through music and voice needs to have a reverberant ambiance, and lay-in panel ceilings will dampen this liveliness, especially if the pews are padded and the floor is carpeted.

Just as you would expect careful structural analysis of your building to ensure its strength and safety, you should have acoustics mathematically computed and predicted to ensure that your new sanctuary meets your worship needs.

Michael Jarzabkowski is the managing director of Sound Scene Acoustics Inc., in New Haven, Conn. He has worked in the field of acoustic consulting for 17 years and notes that many churches contact him to modify newly completed facilities. Had they engaged an acoustic consultant in the early stages of design, he says, much of the their additional expense and inconvenience could have been avoided. For more information, visit http://home1.gte.net/mjarzo or call (203) 436-3513.