A question about propagation constant in wave propagation equation

overgift

Now I'm studying acoustic waves. One question in my mind is propagation constant. It is:

[tex]\gamma = \alpha + j*\beta[/tex]

while the [tex]\alpha[/tex] is attenuation constant, [tex]\beta[/tex] is phase constant. Phase constant I can understand and calculate, but how about the attenuation constant. The literature says it is: e^[tex]\alpha[/tex] = abs(A0/Ax)

where A0 is the amplitude at the source of the wave, Ax is the amplitude at some x distance of the wave.

what my question are:

Is there any other way to find out or calculate the attenuation constant. Since I'm doing a simulation of an acoustic wave, I cannot give correct parameter without knowing the attenuation constant.