Page 290 - The Master Handbook Of Acoustics

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REFRACTION OF SOUND

horizontal sound speed gradient and therefore very little horizontal
refraction. Sound tends to be spread out in a thin sheet in this sound
channel at about 700 fathom depth. Spherical divergence in three dimen-
sions is changed to two-dimensional propagation at this special depth.
These long-distance sound channel experiments have suggested
that such measurements can be used to check on the “warming of the
planet” by detecting changes in the average temperature of the oceans.
The speed of sound is a function of the temperature of the ocean.
Accurate measures of time of transit over a given course yield infor-
mation on the temperature of that ocean. 3

Refraction of Sound in Enclosed Spaces
Refraction is an important effect on a world-sized scale, how about
enclosed spaces? Consider a multi-use gymnasium that serves as an

Sound
speed

Depth S

A B
FIGURE 12-7
How the long range sound experiment of Fig. 12-6 was accomplished; (A) sound speed
decreases with depth in the upper reaches of the ocean (temperature effect) and
increases at greater depths (pressure effect) creating a sound channel at the inversion
depth (about 700 fathoms). (B) A ray of sound is kept in this sound channel by refrac-
tion. Sound travels great distances in this channel because of the lower losses.