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

264 11. Acoustics of Enclosed Spaces: Architectural Acousticsrange is 1.8 s (occupied). Another example of a great rectangular hall is the venerableGrösser Musikvereinssaal (1870) in Vienna which has a reverberation time of2.05 (occupied) in a volume of 530,000 ft 3 . Its superior acoustics can be attributedto its relatively small size, high ceiling, irregular interior surfaces and the plasterinterior (Beranek, 2004).A fan-shaped hall accommodates, through its spread, a larger audience withincloser range from the sound source (stage). It features nonparallel walls thateliminate flutter echoes and standing waves; and most audience members canobtain a pleasing balance between direct and reflected sounds. A disadvantagein terms of early time delay gap is the distance from the side walls. Often it isnecessary to add a series of inner reflectors or canopies hanging from ceilings overthe proscenium area to maintain articulation and other acoustical characteristics.Many architects in the United States have resorted to the fan-shaped hall design inorder to accommodate larger audiences while retaining an appreciable degree ofboth visual and aural coupling to the stage area. Relatively modern examples ofthis design are the Dorothy Chandler Pavilion (1964) in Los Angeles; the OrchestraHall (completed in 1904 and most recently renovated in 1997, Chicago; the EastmanTheater (opened in 1922 as a movie theater and converted into a concert hallin 1930) in Rochester, New York; and the Kleinhaus Music Hall (1940, designedby Eliel and Eero Saarinen) in Buffalo, New York.Over a number of centuries horseshoe-shaped structures have been used as thepreferred design for opera houses and concert halls of modest seating capacity. Thisdesign provides for a greater sense of intimacy, and the textures of convex surfacespromote adequate diffusion of sound. The multiple balconies allow for excellentline of sight and short paths for direct sound. The La Scala Opera House (Figures11.11a, b) in Milan is probably the most notable example of the horseshoe design. Itwas opened in 1778. This edifice, formally known as Teatro alla Scala, was closedin 2001 for 3 years to undergo a badly needed renovation. A tubular structure anda 17-story fly tower designed by Mario Botta were added to provide stagecraftstorage, dressing rooms, and rehearsal rooms. In addition to repairing the ravagesof time on the structure, modern stage machinery and new wiring were installed,as well as a new heating, ventilation and air conditioning system. The acousticswere improved by the prominent acoustician, Higini Arau from Barcelona. Othercelebrated examples of the horseshoe design are the Carnegie Hall (completed1897, renovated 1983–1995) in New York City and the Academy of Music (thefirst opera house in the United States, opened in 1857) in Philadelphia.Nearly all concert halls have balconies, which were designed to accommodateadditional seating capacity within a smaller auditorium volume, so that listenerscan sustain an intimate relationship with the stage. The depths of the balconies generallydo not exceed more than twice their vertical “window” (opening) to the stage.In fact a smaller ratio is desirable to minimize undue sound attenuation at the rearwall. A rule of the thumb in contemporary acoustical design: the depth of the balconyshould not exceed 1.4 times its outlook to the stage at the front of the balcony.In all types of auditorium design, ceilings constitute design opportunities fortransporting sound energy from the stage to distant listeners. In Figure 11.12, it is