### Exponentially Decaying Traveling Waves

Let
denote the decay factor associated with
propagation of a plane wave over distance at frequency
rad/sec. For an ideal plane wave, there is no ``spreading
loss'' (attenuation by ). Under uniform conditions, the
amount of attenuation (in dB) is proportional to the distance
traveled; in other words, the attenuation factors for two successive
segments of a propagation path are *multiplicative*:

*exponential*function of distance .

^{3.3}

*Frequency-independent air
absorption* is easily modeled in an acoustic simulation by making
the substitution

**Next Section:**

Frequency-Dependent Air-Absorption Filtering

**Previous Section:**

Program for Acoustic Echo Simulation