Design for Acoustics
by James Cowan
From the theaters of ancient Greece to those of the 21st century, architectural acoustics has been a key consideration in design. Only within the past century, however, have we been able to scientifically understand and predict the behavior of sound both indoors and outdoors. It is through this understanding that acoustics has evolved from a black art into an established field of engineering.
In addition to the basic principles of acoustics, architects must understand how they can be effectively incorporated into architectural design. This understanding comes partly through mathematical tools and also from seeing and hearing the results of case studies in a variety of applications.
The acoustics within a room depend on the key issues of reverberation, room shape, and interior noise control. Reverberation, the buildup of sound energy in a room as a result of repeated reflections of sound waves off all room surfaces, is in turn affected by the following considerations:
Size: Minimize the room volume where low reverberation times are necessary (speech auditoriums), and choose the proper larger room volume for cases where medium or high reverberation times are required (halls for music).
Absorption: Add absorptive materials to reduce reverberation and add reflective or diffusive materials to add reverberation.
Low frequency absorption: Use Helmholtz resonators, diaphragmatic absorbers, or plenum absorbers for large rooms having reflective surfaces and in need of speech intelligibility.
Speech intelligibility: For large rooms, use a distributed sound system with appropriate delays between loudspeakers and focused low-level loudspeaker systems for reverberant rooms.
This article is excerpted from Architectural Acoustics Design Guide by Acentech and James Cowan, with permission of the publisher, The McGraw-Hill Companies. >>>
Spivey Hall, Clayton College and State University, Morrow, Georgia, was designed to allow adjustable reverberation times.
Photo: Rion Rizzo, Creative Sources Photography
Plan and sections for Spivey Hall show retractable curtains which can be tuned to adjust reverberation.
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