JBL Control 23 Owner's Manual page 10

• Wind - Wind gives the illusion that a sound is coming from
a different direction than it really is. This creates a resultant
propagation vector (see diag. 1 ). When sound propagates
with the wind it tends to refract downward, and against the
wind refract upwards (see diag. 2), (*refraction is the term
used to describe the bending of sound).
CROSS WIND CROSS WIND
I
i
I ·: . . . . . . :
I
:•-. 1
:~ ~ I
l, ::
~
!
',J.!
1
I
I
1 1
1
j
PROPAGATiqN
~
VECTOR
l
j
1
CROSS WIND
----~---------.·--------~
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•Temperature- Temperature differences also have a small
effect on sound propagation. Hot air is less dense than cold.
Sound travels faster in a less dense medium and therefore
speeds up as air gets warmer, and slows down as air gets
cooler. The result is the refraction of sound. For example this
may manifest itself as sound propagates over a cool body of
water on a hot day. The sound will tend to "bounce" along
the surface of the lake and travel a lot further than the
Inverse Square Law may dictate (see diags. 3
& 4).
SOUND OUTDOORS
From the speakers to our ears - Since you usually want a target
background SPL of about 70dB - 80dB to your listeners, keep in
mind the Inverse Square Law, which states that in a free field with no
walls, floor, or ceiling, the intensity of sound decreases with the
square of the distance. For example when you double the distance
between the speaker and your listener's ear, the SPL decreases by
6dB (i.e. If a speaker's output is 1 OOdB SPLat 10 feet away, at 20
feet away the SPL is decreased to 94dB.) Don't forget, a 1 OdB drop
will sound "half as loud".
/
-----
-............
---· - -- - '
' - COLD AIR
~'' ,, ,r
~~ ~,
WATER