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I I ,I I I I I I I I I I I' I I I I I I Jf Churches with adequate acoustics are all very tall spaces -- as required to allow longer reverberation times to support choral and organ music, and congregational singing. For churches with a seating capacity of 800 or more seats, the ceiling heights are frequently as high as 90 ft. They are rarely less than 60 ft. RLC's proposed Worship Center is not a concert hall. But as a comparison, most successful concert halls in the world have ceiling heights in the neighborhood of 60 ft. In addition, typically there is a minimum of 10 ft required above the ceiling for ductwork, structure, and roof construction, which increases the outside height of those buildings accordingly. We analyzed how RLC needed to use this building and the fixed wall dimensions HGA specified after working out the seating. We initially concluded that the Worship Center required a volume calling for a ceiling height of 62 feet, on top of the proposed basement, for adequate acoustics. To address that height, RLC's design team eliminated the basement and lowered the main floor to the level of the baseball field, which reduced the overall height by one full story. The design team further requested that AD develop approaches to meet RLC I S acoustic requirements with a lower roof. As a result of that process, we have developed a unique acoustical design for the Worship Center, which now allows a longer reverberation time to be developed with less volume (in other words a lower ceiling height) than normal. In our design, there is a second ceiling surface in the room considerably below the building ceiling to partially decouple the volume above it from the volume below it. The space above behaves as a partially coupled reverberation chamber, and feeds lower level reverberation back down into the seating area, creating a longer reverberation time than is possible in a standard room design. In other words, this unique acoustical design allowed us to reduce the proposed ceiling height of the building 9 feet -- from 62 feet down to 53 feet. By adding movable sound absorbing or reflecting materials throughout the Worship Center, this design provides the additional benefit of allowing musicians to tI tune " , or adjust the acoustical properties of the Worship Center. In addition to the styles of music represented by religious pipe organ, choir, congregational singing and orchestral accompaniment, the combination of a partially decoupled volume and movable acoustically absorbing materials extends the range of acoustical conditions to encompass requirements for the spoken word and amplified instrumentation. That by-product of this design addresses the Church's critical ministry and worship requirement for a building which will also accommodate 'laltemate" worship liturgy demanded by members and guests, such as gospel, jazz, and Christian rock music styles. This flexibility should also make it an attractive venue for a wide range of secular community events. The initial design height was reduced one story by removing the basement, and an additional nine feet through innovative acoustical design. Even with this uniquely efficient design, the nominal building height is about 10 ft above the RM 1 zoning height specification. I understand from HGA that matching the existing two building levels requires that the building walls be a minimum of 25 feet above the baseball field grade. To fit within the 30 foot R-1 height specification, the roof could not extend more than ten additional feet up. Our professional opinion, which can be confirmed by listening in other similar facilities, is that reducing the interior volume to that level would result in severely degraded acoustics for musical worship expression. Compared to proper acoustics, the sound would be lacking in excitement, harsh and unresponsive. In our experience, the degradation in acoustical performance would be clearly noticeable and irritating to most listeners. The acoustics will almost certainly be a great source of frustration to the musicians, creating almost impossible conditions for them. Roseville Lutheran Church - 2 - October 21, 1994