Page 15 - Winter 2010

The final result, shown in Fig. 7, was a ceiling structure of stunning beauty and great practicality. The acoustical absorption was what the City of Richmond had requested. As Rick Talaske pointed out in the final report, not only was the absorption on target, the lack of high frequency absorption from the ceiling was offset by the high frequency absorption provided by the air contained in the large room volume. The saw tooth shape of the vees also provided helpful diffusion to reduce focusing and echoes.
The building, with its ingenious roof structure, has attracted worldwide attention and received several presti- gious awards. These include an Award of Excellence for Innovation in Architecture, in the Science category, from the Royal Architectural Institute of Canada, and the 2009 Award for Sports or Leisure Structures, from the Institution of Structural Engineers, UK.AT
StructureCraft sent an engineer down to Los Angeles, who took the sample apart, discovered the problem, and rearranged the mineral wool. At the suggestion of Rick Talaske, another acoustical engineer on the project, StructureCraft also added additional 1 inch thick mineral fiber material on the inside faces of the plywood bulkheads. The sample was retested and the result, shown in Fig. 6, met the design criteria.
It is interesting that at the low frequencies the tests yield- ed the absorption coefficient value of 1.2 that I had predicted. At the higher frequencies the shorter wavelengths caused the sound to interact with the solid portion of the vee rather than spanning open portions of the slotted surface, thereby reduc- ing the absorption. The absorption values greater than 1.0 are due to the additional area from the angled surface compared to the flat ceiling area used in the ASTM test standard.
Marshall Long received a BSE degree from Princeton University in 1965, attended the University of Grenoble in France and the University of Madrid in Spain in 1966. He received M.S. and Ph.D. degrees in engineering from UCLA in 1971. While still a graduate student, he founded his own acoustical consulting firm, now in its 38th year. Marshall Long Acoustics specializes in architectural acoustics, audio visual design, noise and vibration control, and other technical areas related to acoustics. He enjoys sailing, judo, soccer, reading, and writing, and is living with his family in Sherman Oaks, California. He is a Fellow of the Acoustical Society of America.
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