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

11.2 Sound Fields 245Figure 11.1. Photograph of the large anechoic chamber at the Lucent Bell Laboratoryin Murray Hill, NJ. Dr. James E. West, a former president of the Acoustical Society ofAmerica, is shown setting up test equipment. (Courtesy of Lucent Technologies.)listener in a fairly typical auditorium can be classified into two broad categories: thedirect (free field) sound and indirect (reverberant) sound. As shown in Figure 11.3,the listener receives the primary or direct sound waves and indirect or reverberantsound. The amount of acoustic energy reaching the listener’s ear by any singlereflected path will be less than that of the direct sound because the reflected path islonger than the direct source–listener distance, which results in greater divergence;and all reflected sound undergo an energy decrease due to the absorption of eventhe most ideal reflectors. But indirect sound that a listener hears comes from a greatnumber of reflection paths. Consequently, the contribution of reflected sound tothe total intensity at the listener’s ear can exceed the contribution of direct soundparticularly if the room surfaces are highly reflective.Figure 11.2. Sound diffusion resulting from multiple reflections.