Handbook for Sound Engineers

1324 Chapter 34

ing) the reflecting surface, is to simply aim the loud-
speakers away from the offending surface. Narrow
coverage angle loudspeakers and constant-directivity
horns may help.
Echoes may also be created by the sound system
because of poor layout or because of poor use or nonuse
of electronic signal delay. Fig. 34-83 shows one
example of an artificial echo caused by poor loud-
speaker layout.
One other source of artificial echoes, poorly under-
stood by many designers, is related to feedback. Any
sound from the loudspeakers that reaches the system
microphone may be delayed by relatively long times in
an outdoor system. This sound can be picked up by the
microphone, reamplified, and emitted from the loud-
speakers as an echo that cannot be distinguished from
an echo created by a reflecting surface.
There are several ways to help solve this problem.
One is to enclose the talker and microphone in a rela-
tively soundproof room. In large outdoor stadiums, this
is often the easiest way to avoid the regeneration type of
echo. Another potential solution is to use a
noise-canceling microphone located close to the talker’s
mouth. Close talking any system microphone will help,
of course, because it allows reduction of system gain
and an equal reduction of the reamplification of an
echo. A noise gate set to turn off the microphone
quickly after the talker stops talking may also help
prevent regeneration echoes. This technique, however,
will work well only in a situation where the microphone
is relatively close to the talker’s mouth.
The announcer on the field hears an echo that no one
else in the stadium hears. That’s because announcers

first hear their own voice and then, delayed sometimes

by as much as half a second or more, they hear their

voice as an echo from the loudspeakers. This can be

very confusing to an inexperienced announcer and may

be the cause of the failure of many prepared speeches

given to graduating classes in a football-field setting.

For the small football field with split bleachers, the

distributed system concept may help since the sound is

primarily aimed at the bleachers and not at the field.

Even if there are some horns aimed at the field, they

will normally be closer to the field than the horns on a

typical scoreboard cluster. Thus, the signal delay and

echo problem will be decreased.

Another partial solution to this problem is to give the

announcer a local monitor loudspeaker (or headphones

in an announce booth). The sound from this monitor will

partially mask the echo from the cluster and may allow

even an inexperienced talker to speak comfortably.

34.6.3.4 Dealing with Long Distances

Modular/concert-style line arrays may seem like an

ideal way to throw sound over long distances outdoors.

However, a typical line array has wide horizontal dis-

persion which may not be desirable. Also, few line

arrays are rated for continuous outdoor exposure.

Thus, when a distributed system is not possible, a

component cluster consisting of high-efficiency,

high-power handling and narrow-coverage,

constant-directivity horns is probably better than either

line arrays or packaged loudspeaker systems for

long-throw applications, Fig. 34-84.

Figure 34-83. An artificial echo caused by poor layout of loudspeakers.

Poor placement

Left loudspeaker

Proper placement

Right loudspeaker

Bleachers Bleachers

Playing field