Handbook for Sound Engineers

Sound System Design 1259

Most column line arrays are designed from
cone-type loudspeaker components or ribbon drivers
that have very wide horizontal dispersion. As in the
concert line-array case, the system designer must
confirm that the resulting side-wall reflections will be
beneficial for the listeners.
Line arrays offer another benefit to the system
designer. For some distance from the line array, the
sound level decreases only 3 dB each time the distance
from the line array is doubled. Contrast this to normal
inverse-square-law loss of 6 dB per doubling of
distance. This makes it possible to keep the Lp more
constant in an audience area and may also help reduce
feedback problems. This effect is frequency dependent
and is limited to a distance of about two to two and one
half times the height of the array.
Some line arrays include sophisticated electronics
and computer software and are steerable. This allows
the system designer to aim the vertical dispersion
precisely at the audience. Some line arrays even allow
two or more lobes that can be aimed at different sections
of the audience.
See Chapters 17 and 18 for more information on
packaged loudspeaker systems and line arrays.

34.3.1.6 Choosing Loudspeakers

Besides the obvious question of budget, there are sev-

eral other considerations in choosing loudspeakers that

apply to both packaged loudspeaker systems and line

arrays.

34.3.1.6.1 Power Handling

The loudspeaker system should be able to handle the

expected power output of the chosen power amplifier

for an extended period of time over the full-rated fre-

quency range of the loudspeaker.

34.3.1.6.2 Frequency Range and Response

The loudspeaker’s response should be smooth over its

intended operating range. If the system will be used pri-

marily for voice, a loudspeaker system whose low-fre-

quency response is limited to 70 or 80 Hz should

suffice. For music, the system’s low-frequency response

should extend down to 40 Hz or below. Frequencies

below 40 Hz are limited to a few instruments, such as

pipe organ, keyboards and synthesizers, and bass drums

( kick drum). When it is necessary to reinforce these

very low frequencies, use a separate subwoofer system

to avoid the added stress these low frequencies would

place on the normal system woofers.

34.3.1.6.3 Sensitivity

Sensitivity is an indication of the loudspeaker’s effi-

ciency. A loudspeaker’s sensitivity is the LP (sound

pressure level) in dB the loudspeaker will produce at

one meter, on-axis, when the input power is one watt.

High sensitivity is an advantage because it increases

maximum LP. Remember that a decrease of only 3 dB

in sensitivity means double the amplifier power is

needed to maintain the same LP.

34.3.1.6.4 Coverage Pattern

Choose the coverage pattern according to the system

needs. Packaged loudspeaker systems commonly offer a

short-throw (90° × 40°) or medium-throw (60° × 40°)

coverage pattern. Some packaged loudspeaker systems

may offer wider or narrower coverage patterns. As men-

tioned, most line arrays have narrow vertical dispersion

and wide horizontal dispersion.

Separate horns and woofers are seldom used as the

main components in loudspeaker clusters but may be

useful for special purposes such as long-throw or

balcony coverage or very wide-angle near-throw.

Component horns are available in short-throw,

medium-throw and long-throw coverage angles.

Long-throw component horns are usually 40° horizontal

by 20° vertical and are commonly needed only in large

concert systems and permanently installed systems.

Medium-throw component horns are usually 60° hori-

zontal by 40° vertical and are valuable in many portable

as well as permanent systems to reach farther back in an

audience. Short-throw component horns are usually 90°

or 120° horizontal by 40° vertical and are used to reach

the front of an audience or may be used to cover an

entire audience in a small portable system.

34.3.1.6.5 Evaluating Loudspeaker Sound Quality

Sound quality is primarily a subjective evaluation,

which means that personal tastes play an important part.

However, the goal of a sound reinforcement system is

not to alter but to reinforce and, to some extent, to

enhance the sound of a performance. Thus, the subjec-

tive evaluation of the sound quality of a loudspeaker