RCF TTL31-A, Руководство пользователя

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CLIMATIC EFFECTS
When working in large venues or outdoors it’s always necessary to remember that sound propagates through air and is
affected by air temperature, humidity and wind.
EFFECTS OF TEMPERATURE GRADIENTS ON SOUND
PROPAGATION
If sound is propagated over large distances outdoors, its behaviour
may seem erratic. Differences (gradients) in temperature above ground
level will affect propagation as shown in next figure. Refraction of
sound refers to its changing direction as its velocity increases slightly
with elevated temperatures. At next figure, particular A, we observe
a situation which often occurs at nightfall, when the ground is
still warm. The case shown at B may occur in the morning, and its
“skipping” characteristic may give rise to hot spots and dead spots in
the listening area.
EFFECTS OF WIND VELOCITY AND GRADIENTS ON SOUND PROPAGATION
Next figure shows the effect wind velocity gradients on sound propagation. The actual velocity of sound in this case
is the velocity of sound in still air plus the velocity of the wind itself. The following figure shows the effect of a cross
breeze on the apparent direction of a sound source. The effects shown in these two figures may be evident at large rock
concerts, where the distances covered may be in the 200 - 300 m range.
Effect of wind velocity gradients on sound propagation Effect of cross breeze on apparent direction of sound
EFFECTS OF HUMIDITY ON SOUND PROPAGATION
Contrary to what most people believe, there is more sound
attenuation in dry air than in damp air. The effect is a complex one,
and it is shown in the next figure. Note that the effect is significant
only at frequencies above 2 kHz. This means that high frequencies
will be attenuated more with distance than low frequencies will be,
and that the attenuation will be greatest when the relative humidity
is 20 percent or less.
Effects of temperature gradients on sound propagation
Absorbption of sound in air vs. relative humidity