What is the sonic signature of a spiritually nurturing place of worship? Can a church achieve the visual aesthetic appearance it desires and still have intelligible speech in the nave? These are two questions recently raised in designing the new landmark Serbian Orthodox Christian church in Saratoga, CA called St. Archangel Michael. BCA Architects of Fremont, CA teamed up with acoustical and audiovisual engineering consultants Shen Milsom & Wilke of San Francisco, CA to tackle these interesting challenges. The congregation of the church led by Father Slobodan Jovic expressed a strong desire for its Byzantine style church to look and sound “old world” and to be constructed to last hundreds of years. As the design architects at BCA quickly learned, there is much faith-related design direction imposed for such a church, including integrating Golden Ratio proportions with a high domed ceiling, concave alcove apses, concentric arches, a choir balcony, and a bell tower – all to express “God is with us”.
With a small congregation capacity of approximately 250 people, the church originally wanted no amplified sound system in the nave and hoped for good speech intelligibility with natural acoustics. Possessing a 64,000 ft.3 volume, hard sound reflective interior finishes, and multiple concave surfaces, the church would exhibit a naturally long reverberation decay time. While this natural reverb appealed to the church as it enriches the sound of chanting and a cappella singing, it would be in direct opposition to good speech intelligibility in the nave. Shen Milsom & Wilke joined the design team to acoustically model the proposed church design. SM&W produced a computer model of the church and analyzed sound reflection behavior with the method of ray trace simulation. The model predicted the fully occupied church would possess a 2.5 second reverb decay time as well as dense areas of focused reflections from concave surfaces. The “decay time” is commonly measured with RT60, the time it takes in seconds for sound reflections to diminish by 60 dB in the space. The model was also used to evaluate speech intelligibility of unamplified voice using a metric of Speech Transmission Index (STI). This is a decimal scale from 0 to 1, ranging from unintelligible to perfectly intelligible. Spoken word venues generally target reverb decay times of 1.0 seconds or less and an STI score of 0.5 or higher across the audience area. In the case of St. Michael’s 2.5 second reverb and audience areas reaching as low as 0.2 STI, unamplified voice appeared impractical. BCA questioned engineers at SM&W, “What can we do with surface applied interior acoustical treatments in the nave?”
The design team set about introducing sound absorbing materials into the acoustical model in addition to the terrazzo, glass, plaster, and wood. They discovered that it would take 2,200 ft.2 of absorptive material applied on the walls and ceiling to reduce the reverb decay time to 1 second. The next design challenge appeared when the architects explained that nearly every square inch of wall and ceiling would be painted with decorative fresco paintings. This could be overcome by using acoustical plaster such as Star Silent that can receive light painting without diminishing its acoustical absorption. A sample painting was commissioned from St. Archangel Michael’s fresco artist. While the plaster took the paint okay, it did not produce the desired crispness of image the artist wanted, and when the proposed material cost impact came back at $110,000 this option fell out of the design. In its quest to reduce the reverberation, the design team was again reminded that the church in fact wanted reverberation in order to sound old world and spiritually engulfing. To drive the point home the church supplied sample recordings of chanting and singing from its faith as captured in churches they wanted to emulate.
SM&W suggested to the architects, “let’s switch our focus from acoustical treatments to use of a sound system to overcome the challenging room acoustics”. Skeptical at first, the church pursued this investigation in hopes that it could keep its lush reverb and fresco paintings but still have good speech intelligibility. Loudspeakers then replaced the simulated human voice in the computer model. A special type of speaker called a line array was selected because, using its tall column of multiple drivers, it can project a tightly focused beam of sound that can be electronically steered in the vertical domain. By projecting such a focused pattern of sound much less reverberation and reflections were excited in the church model and speech intelligibility improved dramatically. A pair of Renkus Heinz Iconyx IC8 speakers was integrated into recessed niches flanking the stage area of the apse. The niches would be skinned with micro-perforated metal grills to conceal the speakers, and further hidden by fresco-painted removable panels on each column face camouflaging the niches when not in use. While line arrays can actually project more than one beam of focused sound by digital signal processing tricks, it was decided to cover the choir balcony with satellite Meyer Sound MM4 speakers integrated into the balustrade. This further limited how many room reflections were excited, and was simply accommodated by properly time aligning the satellite speakers to the main speakers using electronic time delay.
Supporting audio devices such as a Presonus Live/Studio 16.4.2 digital mixing console with programmable memory presets (for easy use by the congregation) and ultra inconspicuous DaCappo DA-12AE over-the-ear wireless microphones were incorporated in the design to achieve a simple yet seamless setup. The architects at BCA worked diligently to conceal the equipment rack, mixing console, speakers, and cable pathways within the architecture to make the sound system as discrete as possible in this “old world” looking church. Judicious limiting of the total system sound level would be exercised to give just enough speech boost without sounding like a Grateful Dead rock concert. An added bonus to the church was the ability to now play electronic sound cues of recorded bells in the services, which previously would have been cobbled together in some less elegant way. With a projected total installed system cost of $75,000, the ability to retain the lush reverberation and fresco painting, and dramatically improved speech intelligibility, this new design direction was well received by the church and design team. The church is just now beginning construction in early 2010. It will be exciting to learn if the proper balance between “old world” and “new technology” will foster the spiritual reverence the congregation seeks.