Handbook for Sound Engineers

Sound System Design 1275

essentially the same distance from the listener (and thus

not acoustically delayed). Design of each cluster in such

a system is straightforward. Choose a seating area that

can be easily covered by a single cluster. Calculate the

difference in distance from a typical listener to adjacent

clusters. Avoid wide spacing between clusters that could

cause a listener hearing two clusters to hear the second

cluster as an echo of the first. Provide sufficient overlap

between coverage areas to insure adequate sound pres-

sure level to all listeners but avoid wide overlap areas to

prevent the problems inherent in the split cluster dis-

cussed in Section 34.3.2.3.

This same approach applies to smaller loudspeakers

distributed around the concourse in an arena or along

the sidewalk leading to a theme park attraction.

34.3.3.8.3 Equalizing the Distributed Cluster System

Equalization is discussed in more detail in Section

34.5.2.2. However, if all clusters in a distributed cluster

system are the same and are covering areas with similar

acoustics, equalization may be performed for a single

cluster and duplicated for the other clusters. Check the

response of the other areas to confirm the equalized

curve is similar. If clusters are covering acoustically dif-

ferent areas or if they are designed for different loud-

speakers, each type of area or loudspeaker must receive

separate equalization (the central cluster plus under-bal-

cony distributed system, for example).

34.3.4 Crossover Networks and Biamplification

Loudspeaker crossover networks are also discussed in

Chapter 17.

34.3.4.1 Definitions

Crossover Network. A crossover network is a filter
network that routes high frequencies to a high-fre-
quency loudspeaker and low frequencies to a low-fre-
quency loudspeaker. If the crossover network is part of
a biamplified system, it will do its frequency division
prior to the power amplifiers. Three-way and four-way
crossovers perform the same function but divide the fre-
quencies into more sections.

Passive Device. A passive device uses no active compo-
nents (tubes, transistors, ICs) and needs no power
supply (ac, dc, battery). The crossover network in a
typical packaged loudspeaker system is a passive
device.

Active Device. An active device uses one or more

active components and requires some type of power

supply. An electronic crossover, used in a biamplified

system, is an active device.

Biamplified System. A biamplified system uses an

electronic crossover (commonly a module in a DSP)

and it uses separate power amplifiers for the high- and

low-frequency loudspeakers, Fig. 34-34. A triamplified

system is a three-way loudspeaker system with a

three-way electronic crossover and separate power

amplifiers for the low-, mid-, and high-frequency loud-

speakers. To simplify, we often speak of triamplified

and multiamplified systems as being biamplified.

Head Room. Headroom is the difference, in decibels,

between the peak and rms levels in the program

material.

34.3.4.2 Advantages of a Biamplified System

One advantage of a biamplified system is that it can

actually provide more head room per watt of amplifier

power than a system with a traditional (loudspeaker

level) passive crossover.

The reason this happens is that most music, espe-

cially popular music, is bass heavy; that is, there is

much more energy at low frequencies than at high

frequencies. When both high and low frequencies are

present in a program, the high-energy bass frequencies

will dominate the output of the system power amplifier

Figure 34-34. Biamplified and nonbiamplified systems.

Passive high level

crossover network

Input Outputs

Power

amplifier

From mixer,

equalizer, etc.

HF

Loudspeaker

LF

Loudspeaker

A. Nonbiamplified system.

Passive or active ("Electronic")

low level crossover network

Input

HF

Loudspeaker

LF

Loudspeaker

LF power amplifier

From mixer,

equalizer, etc.

B. Biamplified.

HF power amplifier

Outputs