Handbook for Sound Engineers

Sound System Design 1271

cally use a 12 or 15 inch coaxial loudspeaker compo-
nent, Fig. 34-28.

34.3.3.6.2 Packaged Loudspeaker Systems in
Distributed Systems

Packaged loudspeaker systems are commonly used in
distributed systems in large rooms with relatively low
ceilings. Examples include convention centers, exhibit
halls, and hotel ballrooms, Fig. 34-29.
In these rooms, small, packaged systems may be
hung, face down, in a distributed fashion to cover the
room. The advantages of high-quality packaged systems
in this application are their high output level and their
wider range frequency response in comparison to
typical 8 or even 12 inch ceiling-type loudspeakers.
Rigging safety and fire safety must be considered for
these applications.
Packaged loudspeaker systems like this are also used
for distributed line systems. For example, they may be

installed along the wall of an arena concourse, or

outdoors, along a walkway leading to a theme park

attraction.

34.3.3.7 Designing the Distributed Ceiling System

Skipping Question 2 momentarily, here are discussions

of the other three questions for a distributed ceiling

system.

34.3.3.7.1 Question 1: Is It Loud Enough?

One of the advantages of a distributed system is that a

typical listener is about the same distance from the near-

est loudspeaker as any other listener. In addition, these

distances are usually short compared to the critical dis-

tance Dc. Thus, the direct sound, not the reverberant

sound, is the primary component of the LP reaching the

listener and the electrical power required (EPR) equa-

tion for the simplified system, Eq. 34-6, can be used.

Use a single loudspeaker for this calculation for the

minimum-overlap configurations (see Question 2, fol-

lowing). For the 50% overlap configurations, subtract

3 dB from the desired sound pressure level for the cal-

culation of EPR to a single loudspeaker, since the equiv-

alent of at least two loudspeakers will be covering each

listener. If the room is highly reverberant and/or the

ceiling height is sufficient to make the reverberant field

a significant component of the sound at the listener’s

ears, the indoor EPR equation (Eq. 34-16 or 34-17) may

be used. To include the effect of the multiple sources,

use a value of Q=3/N, where N is the total number of

distributed loudspeakers in the critical distance Dc cal-

culation. The number 3 is a typical Q for a distributed

Figure 34-27. Typical ceiling loudspeaker components.
Courtesy Atlas Sound.

Figure 34-28. Large ceiling-type loudspeaker systems.
Courtesy Lowell.

Figure 34-29. A family of packaged loudspeaker systems

for distributed applications. Courtesy JBL Professional.