Line Arrays — History and Theory
Mention is made of the vertical orientation of sound
sources as far back as 1896. Line arrays were also popular in
the 1950s and 60s because of the ability to provide excellent
vocal range intelligibility in reverberant spaces.
Figure 1,
Figure 2
and
Figure 3
are excellent representations of high
performance “vocal range” line arrays. These line arrays, like
all vertically oriented sources in the past were, what could best
be termed, limited bandwidth line arrays.
Figure 3
shows an Electro-Voice line array from the 1970s.
It represents a relatively elegant solution to achieving high vocal
intelligibility. It should be noted that the source separation of
this design is roughly six inches, relating to a wavelength of
2.26kHz. The line array behaved very well up to that 2 kHz range.
It should also be noted in the
Figure 3
that a high
frequency horn was employed above that frequency limit in
order to achieve appropriate extended bandwidth and fidelity
up to and beyond 10 kHz. This is a classic embodiment of a
limited bandwidth line array and as we shall see in this presen-
tation, only recently have solutions been brought to the state
of the art to enable line array technology to truly be full band-
width and extend beyond the 10-15 kHz region.
Before we begin discussing bandwidth for modern day line
arrays, it is important to begin with a discussion of basic
radiation of sound.
Figure 4
represents a spherical shape
whose radius “r ” can vary with time.
Figure 5, Equation 1
describes the acoustical performance
of this pulsating sphere. This pulsating sphere, or simple
source is a useful theoretical tool describing the mathematics
of radiating sound.
Figure 5, Equation 1
ρ
AV
=
(ka)
2
p.c ( V
s
2
) ave (4
π
a
2
)
1 + (ka)
2
Where:
K =
W
/
C
ρ
AV
= time averaged power
VS = velocity
Figure 5, Equation 2
Condition:Ka << 1
or
λ
>> a
Line Arrays
Figure 1
Figure 2
Figure 4
b = 6''
ƒ = 2.26 KHz
Figure 3
1
