Structural Acoustics

Fundamentals of Acoustics and Structural Acoustics 19

© 2011 by Taylor and Francis Group, LLC

There are two main equations of ray theory. The rst is Snell’s law of refrac-

tion, which states that

V V V V

n

n

1

1

2

2

3

3

cos cos cos cosθ θ θ θ

= = = =

(2.22)

where V

1

, V

2

,…V

n

are the velocities of sound through the various layers of the

medium, which are at different temperatures, as shown in Figure2.3.

The second relation is that the power ow remains constant along a ray

tube (i.e., there is conservation of energy along a ray tube). A ray tube is a

closed surface formed by adjacent rays, as shown in Figure2.4. If the power

ow remains constant alon