Handbook for Sound Engineers

1270 Chapter 34

system, placed under the balcony, with signal delay, can
provide coverage for the under-balcony listeners, Fig.
34-25. A good rule of thumb is that every listener under
a balcony should have good line of sight to the loud-
speaker covering his or her area in order to hear the cen-
tral cluster well. If any part of the central cluster is
shadowed by the balcony, consider a distributed,
under-balcony, signal-delayed system.

34.3.3.3 Multicluster System

A multicluster system could be considered a distributed
system. Also, in the large arenas and exhibit halls men-
tioned previously, horn/woofer components more typi-
cal of a central cluster may be used in the distributed
system simply to produce a higher LP capability.

34.3.3.4 Distributed Column System

One common variation on the distributed system is
called a distributed column system, Fig. 34-26. This
type of system is normally installed in a long, narrow
religious cathedral where a central cluster cannot be
installed for aesthetic reasons. A group of column-type
loudspeakers (or some other type of packaged loud-
speaker systems with appropriate dispersion) are
installed. Electronic signal delay and a localizer loud-
speaker may be included. This system can have the
same problems as the split cluster described earlier,
however, and should be used only in narrow rooms to
minimize these problems.

34.3.3.5 Pew-Back Distributed System

Another distributed variation for churches is known as
the pew-back system. In this system, pioneered by con-
sultant David Klepper, a large number of small loud-
speakers (usually one loudspeaker for every two to three

listeners) is placed on the backs of the pews and facing

the listeners. Signal delay is required. One problem with

a pew-back system is the significant change in D 2 and

loudspeaker Q when the listeners stand up (the listeners

move both farther away from the loudspeaker and more

off axis of the loudspeaker). Another problem is the

large value of N caused by the large number of active

loudspeakers. To partially overcome the N problem, add

a latching relay in each enclosure and a “push-to-listen”

button. This way, loudspeakers in pews with no listeners

will not be turned on, and those loudspeakers will not

uselessly add to the reverberant field intensity.

Both the distributed column system and the

pew-back system are difficult to design and install prop-

erly. As with any difficult design, an experienced acous-

tical consultant may be the best answer to getting a

costly job done right the first time.

34.3.3.6 Loudspeakers for Distributed Systems

34.3.3.6.1 Ceiling Loudspeaker Systems

Typical ceiling loudspeakers are 4 inch or 8 inch

cone-type components that often come in a package that

includes a round metal enclosure, grille, and 70 V trans-

former, Fig. 34-27. Those designed for installation in a

dropped ceiling may also include an optional T-bar sus-

pension system. Some may be UL listed for fire signal-

ing or fire resistance. This type of ceiling loudspeaker is

intended for sound reinforcement, business music, and

paging in applications that do not require high SPL

levels.

Larger ceiling loudspeakers and enclosures are

designed for use in convention centers, arenas, and

other applications that may require mid- to high SPL

levels and a wide frequency range. These systems typi-

Figure 34-25. Central cluster plus under-balcony distrib-
uted loudspeakers on signal delay. Courtesy Bosch/
Electro-Voice.

125'

6'

Figure 34-26. A distributed column loudspeaker system

with signal delay. Courtesy Bosch/Electro-Voice.

Frontal

locator

loudspeaker 45 ft

maximum

Column loudspeakers

Pillars