THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

274 11. Acoustics of Enclosed Spaces: Architectural Acousticsalso a 150-member chorus. The walls and the ceiling of the stage incorporatecontours and angles precisely planned to enhance cross-room reflections so thatmusicians can hear each other from one side of the stage to the other and fromfront to back. When an orchestra performs at high volume it is often difficult formusicians playing in the high register to hear instruments in the lower registers. Tocircumvent this problem, the orchestra risers feature a platform system, researchedand designed by the acousticians and musicians together, that allows the musiciansto feel the vibration created by the cellos and bass instruments. The riser system,essentially a floating floor with rigid interconnections and resilient materials justbelow the floor surface, acts to maximize cross stage vibrations. This enables amore precise ensemble and tonal balance.To compensate for the lack of reflected sound in an outdoor setting and the lackof envelopment, modern technology was recruited to improve the sound environmentby blending architecturally created and electronically processed sound. TheJay Pritzker Pavilion, which replaces the Petrillo Music Shell constructed in 1931and still in use on a more limited basis, is the first orchestral facility that distributessound by using an overhead steel trellis structure from which loudspeakers are suspended(Figure 12.20). The trellis area that incorporates the network of speakersis 100 m (325 ft) wide by 180 m (600 ft) long. These loudspeakers are strategicallysuspended at predetermined heights and orientations, in concentric circlesoutward from the stage. A distributed sound reinforcement system provides director “frontal” sound to the audience. A separate acoustic enhancement system,Figure 11.20. View from the stage of the Pritzker Pavilion. The trellis overhead of theaudience contains a distributed loudspeaker system.