Handbook for Sound Engineers

Sound System Design 1261

sound system. This is often the case in large indoor

sports arenas.

34.3.2.2 Variations on the Central Cluster

Sometimes, in a long room with a relatively low ceiling,
a second cluster is installed. The second cluster (and the
third if more than two clusters are used) is installed
some distance out in the room and the sound emanating
from these clusters is electronically delayed so that a
listener able to hear both clusters will seem to hear only
one source, Fig. 34-17. The second cluster effectively
divides the room into two rooms, and the first cluster
now only has to cover a room that is half as long.

34.3.2.3 The Split Cluster

One way to install a cluster-type system and preserve
central sight lines is to split the cluster with part on the
left and part on the right, Fig. 34-18. Unfortunately, this
design causes comb filtering in the audience area where
the two clusters overlap.

To minimize comb filtering, minimize the amount of
overlap between the two clusters. This is easier to
accomplish in a room with a central aisle. Another way
to minimize this problem, at least partially, is to lower
the sound pressure level of one of the clusters about
3 dB and use that lower-level cluster to cover only those
listeners who cannot adequately be covered by the other
cluster. Design the louder cluster to cover as much of
the listening audience as possible.

Line arrays are commonly used in a split-cluster
configuration. In particular, column-style line arrays are
popular for this application. Because of their narrow
vertical dispersion and 3 dB attenuation per doubling
of distance, column line arrays can be placed lower than

a typical cluster—often at or just above the audience

head height. Also, they are perceived as more attractive

than other types of loudspeaker systems.

34.3.2.4 Stereo Clusters

For stereo music reinforcement, left and right clusters

are required. In order for every listener to hear the ste-

reo effect, both clusters must cover the entire audience.

Because this conflicts with the guidelines developed in

the previous section, many designers prefer the

Left-Center-Right approach discussed next.

34.3.2.5 Left-Center-Right Clusters

For a system that has both voice and stereo or multi-

channel music, consider a left-center-right cluster

design. In this arrangement, the center cluster primarily

reinforces the spoken voice and the left and right clusters

reinforce the music. It may be difficult for listeners at

the left and right edges of the audience to hear the cen-

tral cluster clearly. In this case, mix a little of the spoken

word into the left and right clusters but delay it slightly

so the voice appears to come from the central cluster.

It may also be difficult for listeners at the left and

right edges of the audience to hear both channels of the

music. One way to reduce this problem is to mix some

of both the left and right channels of music into the

central cluster. Of course, this will reduce the stereo

effect for listeners seated in the center of the audience.

Figure 34-17. Two-cluster (front, back) system. Courtesy
Bosch/Electro-Voice.

73'

40'

73'

100'

127'

Talker Listener L 1

Listener L 2

Listener L 3

Figure 34-18. The split cluster.

Left cluster Right cluster

A

C

B

D