ACOUSTICS

Аннотация

At audible frequencies the wavelength of a sound is long compared with the spacing between air molecules. For example, at 1000 eps, the wavelength A equals 0.34 m, as compared with an intermolecular spacing of 10 m. Now, whenever a portion of any gas is compressed rapidly, its temperature rises, and, conversely, when it is expanded rapidly, its temperature drops. At any one point in an alternating sound field, therefore, the temperature rises and falls relative to the ambient tem- perature. This variation occurs at the same frequency as that of the sound wave and is in phase with the sound pressure