TM 5-805-4/AFJMAN 32-1090
PART A
PART B
Figure 5-4. Effects of Temperature Gradients on Sound Propagation.
(2) TL of barrier. The barrier wall or structure
(5) Atmospheric effects. For wind speeds above
must be solid (no penetrating holes) and must be
about 10 to 15 mph along the direction of the
constructed of a material having sound transmis-
sound path from source to receiver and for dis-
sion loss (TL) that is at least 10 dB greater than
tances over about 1000 feet between source and
the calculated insertion loss of the barrier in all
receiver, the wind bends the sound waves down
octave bands.
over the top of the barrier. Under these conditions,
(3) Width of barrier. Each end of the barrier
the barrier will appear to be very ineffective.
should extend horizontally beyond the line of sight
(6) Terrain-vegetation effects. When both a bar-
from the outer edge of the source to the outer edge
rier and the terrain-vegetation effects of Section
of the receiver building by a distance that is at
5-4 occur simultaneously, only the larger values of
least 3 times the value of h used in the calculation.
attenuation calculated for these two effects should
(4) Large distances. For large distances, sound
be used. The sum of both effects should not be
scattered and bent over the barrier (the path 3
used.
concept in figure 5-5) reduces its effectiveness. It
(7) Another building us a barrier. If the bar-
is suggested that the calculated insertion loss be
rier is another building, there should be no large
reduced by about 10 percent for each 1000-foot
openings entirely through the building that would
distance between source and receiver.
destroy its effectiveness as a barrier. A few small
Figure 5-5. Outdoor Sound Propagation Near the Ground.
5-7
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