Volume 4, Issue 1, January 2008
Index of content:
4(2008); http://dx.doi.org/10.1121/1.2961165View Description Hide Description
This article provides an historical overview of Time Reversal (TR), introduces its basic physics, addresses advantages and limitations, and describes some applications of this very active research area of acoustics. In the Geophysics Group at the Los Alamos National Laboratory, we conduct studies of TR of elastic waves in solids. Our work includes application of TR to nondestructive evaluation of materials, as well as to earthquake source characterization, and ground‐based nuclear explosion monitoring. We emphasize the term elastic waves here to underscore that we include both compression and shear waves, in contrast to purely acoustic waves that are only compressional.
4(2008); http://dx.doi.org/10.1121/1.2961162View Description Hide Description
Perhaps the speed of sound is one of the most fundamental and most often measured attributes of a solid. Acoustic students have been doing such measurements for years, seldom appreciating the wealth of knowledge that can be obtained from the solid from this apparently simple experiment. But to understand exactly what has been measured, what has influenced the measurment, how best to perform the measurement, and how accurately the measurement has been taken has often demanded a lifetime of experience. This paper describes some of the latest techniques that condensed matter physicists now use to probe solids.
4(2008); http://dx.doi.org/10.1121/1.2961163View Description Hide Description
At the beginning of certain sound system design projects there is a moment of panic when the whole thing seems totally impossible. Usually the difficulties arise from a combination of a challenging acoustical environment and complicated client demands. At these times it is useful to take a deep breath and review the overall design objectives, which are relatively simple: (1) distribute direct sound evenly to the listening area, (2) provide adequate intelligibility, (3) deliver sufficient level, frequency response, and natural sound quality for the intended use, (4) leave the listener with the sense that the sound is coming from the source, (5) control feedback at the microphone positions, (6) avoid acoustical defects such as long delayed reflections, and (7) respect the architecture of the space.