Specifications

TI 323 (6.0E)
15 - 36
HFC function of a C4-TOP controller
20
100 1k 10k
20
k
2
0
4
6
-2
-4
dB
Refraction by variation of the wind speed
Note that this filter reduces the available headroom
of the loudspeaker system, and for this reason there
are certain limits for electronic compensation,
depending on distance and required SPL.
4.5.2. Temperature layers
The most obvious example to illustrate the effects of
temperature layers in our atmosphere is an open-air
show. The body temperature of the audience heats
the surrounding air, while the air above them
maintains the temperature of the environment. The
difference in temperature can easily be 10°C or more.
The table below shows the dependency between
wavelength and temperature.
f (Hz) λ
λλ
λ (10°C) λ
λλ
λ (20°C) λ
λλ
λ (30°C) λ
λλ
λ (40°C)
31 10.87 m
35.66 ft
11.06 m
36.27 ft
11.26 m
36.94 ft
11.45 m
37.57 ft
63 5.35 m
17.55 ft
5.44 m
17.85 ft
5.54 m
18.18 ft
5.63 m
18.47 ft
125 2.70 m
8.86 ft
2.74 m
8.99 ft
2.79 m
9.15 ft
2.84 m
9.32 ft
250 1.35 m
4.43 ft
1.37 m
4.49 ft
1.40 m
4.59 ft
1.42 m
4.66 ft
500 64.40 cm
2.113 ft
68.60 cm
2.251 ft
69.80 cm
2.290 ft
71.00 cm
2.329 ft
1000 33.70 cm
1.106 ft
34.30 cm
1.125 ft
34.90 cm
1.145 ft
35.50 cm
1.165 ft
2000 16.85 cm
0.553 ft
17.15 cm
0.563 ft
17.45 cm
0.573 ft
17.75 cm
0.582 ft
4000 8.43 cm
0.277 ft
8.58 cm
0.282 ft
8.73 cm
0.286 ft
8.88 cm
0.291 ft
8000 4.21 cm
0.138 ft
4.29 cm
0.141 ft
4.36 cm
0.143 ft
4.44 cm
0.146 ft
16000 2.11 cm
0.069 ft
2.14 cm
0.070 ft
2.18 cm
0.072 ft
2.22 cm
0.073 ft
Due to the increasing speed of sound at higher
temperatures the wavelength will increase (see
chapter 5. Sphere or Line?). According to Snell's law
the direction of the wave will bend depending on the
thermal layers.
If the warm layer is below the cold layer the wave will
bend upwards.
If the cold layer is below the warm layer the wave will
bend downwards.
4.5.3. Wind effects
The effects described above are more or less static,
however it gets more complex when looking at the
effects caused by the wind. Usually the wind speed is
lower near ground level than at higher altitudes, as a
result if the sound wave travels against the wind the
speed of sound decreases with altitude, and the sound
wave will then be bent upwards.
If the sound wave travels with the wind, the speed of
sound increases with altitude, and the sound wave will
then be bent downwards.
As mentioned before, the behaviour of the wind in the
atmosphere can be erratic. Unpredictable winds
creating whirlpools of rising and falling air may occur,
bending sound waves in all directions.