PERFECT MODEL?

Acoustician Harold Marshall’s successful designs at two halls in New Zealand, as well as his access to a $1.5- million acoustic testing laboratory in Auckland, were important factors in his inclusion in the design team for the Orange County Performing Arts Center.

Marshall, director of the Acoustics Institute at the University of Auckland’s department of architecture, was a participant in a 1981 “design squatter’s seminar” in Costa Mesa. In an interview in his New Zealand office, he recalled that the major problem addressed by the consultants, architects and center officials at the two-week session was the conceptual design of the hall.

In order to accommodate the proscenium stage needed for the performance of opera and theater without compromising the sight lines, the hall needed to be fan-shaped. But, Marshall says, that would have a “disastrous effect on the acoustics for the symphony because the side wall reflections only go to the back corner of the hall in fans,” and sound will be lost rather than being reflected back toward the listener.

Marshall says he proposed an asymmetrical audience arrangement with a symmetrical fan shape. Split-level seating areas within the hall are “articulated with surfaces that provide each section of the audience with its own correct reflection sequence.” The plan was adopted and, after 18 months’ development by acousticians from the firms of Paoletti / Lewitz Associates Inc. and Jerald R. Hyde, the detailed construction and testing on a model one-tenth the size of the center began at the laboratory in Auckland, where large-scale models of facilities can be created and tested.

So precise were the specifications of the Orange County model that it took a specialist six months to build it at a cost of $40,000. The actual measuring program took another three months, Marshall says.

“The measurements were extraordinarily difficult to make. For instance, air conditions had to be simulated, which meant drying the air to 2% or 3% relative humidity.”

All the materials had to be made to scale. Actual chairs, wall panels and carpeting had to be measured and re-created at model scale. The Marshall-designed Christchurch Town Hall, with an audience capacity similar to that of the Orange County facility, was used to measure how much sound would be “absorbed” by members of the audience. This particular method, Marshall says, helps determine what materials--such as seats or paneling--allow for the best possible acoustics.

“The great advantage of large-scale modeling is that it makes the effect of the hall on symphonic music accessible to the acousticians and owners before the hall is built,” Marshall says. “The most spectacular advantage is the subjective evaluation this technique permits.” Marshall, a partner in the Auckland-based acoustic consulting firm of Marshall Day Associates, notes that the assessment of a hall can vary from person to person and from performance to performance and depends on many variables, including mood, comfort, air conditions and view.

Ideal conditions for a “true concert experience” occur only in halls where much of the sound arrives at the listener’s head from the side, he says.

Marshall first put forward the hypothesis of “directed reflection sequences” 20 years ago when reviewing prospective designs for the multipurpose Christchurch Town Hall. That hall subsequently was built with 10 large lateral reflecting surfaces within the shell of the enclosure, incorporating the cantilevered gallery and surfaces both above and below it. He perfected the concept with the design of Michael Fowler Centre in Wellington, New Zealand. When the 2,750-seat Christ-church hall opened in September, 1972, critics and audiences alike were impressed with the acoustics. After his visit there in 1974, conductor Leonard Bernstein told the Christchurch Press: “I’m crazy about it--very envious. . . . What is wonderful about it is the warmth of it and the X-ray clarity of the sound. I was very impressed with that combination of vastness and intimacy that the architects have somehow achieved in the hall itself.”

As with the halls in Christchurch and Wellington, research will continue on the design of the Orange County Performing Arts Center, Marshall says. While testing a scale model is, in Marshall’s view, as accurate and expert as is possible to get in perceiving how sounds will be heard in a room, Marshall admits that science can only partly determine acoustic quality, because, in the end, such a judgment is subjective.

Marshall sees the testing process as a “continuous inter-reaction, an ongoing chain. By its very nature, design means change. Acoustics can never be a closed book.”