Abstract
Damping in acoustics means to the sound absorption. To define the complex density means a viscous damping vibration of continuous system, and to use the concept of complex propagation speed and complex wave number, can explain the phenomenon of wave propagation with damping. The case of non-damping, when wave propagation is one-dimensional acoustic tube, natural mode is formed by overlapping of the traveling wave and the reflected wave, eigenvalue and eigen function is represented by real numbers. The case of uniform Rayleigh damping, eigen function becomes real and eigenvalues becomes complex. However, the natural mode is less likely to be excited due to distance decay. In this study, to reproduce the logarithmic decrement used to excite a natural mode by overlapping wave by uniform distribution excitations for distance decay. Measured complex propagation speed by the method of two types of measured after excitation of damped free vibration natural mode and distance decay measurement in forced oscillation, to pigeonhole the relationship between them.
