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EVX-180B 18-Inch Low-Frequency Reproducer
crest factor. This procedure provides a rig-
orous test of both thermal and mechanical
failure modes.
The EVX-180B has also been power tested
with a two-hour sine wave at minimum im-
pedance so that competitive comparisions
can be made using consistent methods. Con-
tinuous program power is defined as 3 dB
above (double) the continuous sine-wave
power rating.
Recommended Enclosures
The most extended bass, lowest distortion
and best control is usually realized in prop-
erly designed vented enclosures. In such de-
signs, the vent, or port, actually provides the
lowest octave of output. The vent is driven
to full acoustic output by a relatively small
motion of the speaker cone itself, acting
through the air contained within the enclo-
sure. The excursion of the EVX-180B at
these frequencies is much reduced compared
to sealed or open-back enclosures, directly
reducing harmonic distortion and the possi-
bility of speaker "bottoming." Several spe-
cific vented-enclosure recommendations are
shown on the following pages. Alternate
tunings are given so that designers can tailor
the low-frequency response to their specific
needs. Figure 5 shows the maximum long-
term SPL versus frequency. The maximum
output is limited by either: (1) the long-term
thermal power-handling capacity or (2) the
speaker's maximum cone-excursion capabil-
ity, whichever occurs first. Also provided are
recommended enclosures for multiple driver
configurations.
Step-Down Operation
For extra-low bass use, the vent area can be
reduced by one-half, thereby tuning the en-
closure to the "step-down" mode. In step-
down, the tuning frequency is reduced by
half an octave (a factor of 0.7). The result-
ing alignment is then equalized for flat re-
sponse. This procedure results in one-half-
octave lower bass.
Architects' and Engineers'
Specifications
The low-frequency transducer shall have a
nominal diameter of 460 mm (18 in.), over-
2
all depth not greater than 198 mm (7.92 in.),
and weigh no more than 11 kg (25 lb). The
frame shall be made of die-cast aluminum to
resist deformation. The magnetic assembly
shall have an extended pole piece to reduce
inductive variances with excursion, and pro-
vide a symmetrical magnetic field at the
voice-coil gap. Two aluminum rings shall
encircle the pole piece above and below the
magnetic gap, and shall have internal diam-
eters concentric with the internal diameter
of the steel top plate. The upper ring shall be
part of the loudspeaker frame. Both rings act
to reduce flux modulation and provide a heat-
transfer path from the outer diameter of the
voice coil.
The voice coil shall be 100 mm (4 in.) in
diameter and 20 mm (0.8 in.) in winding
length, and shall be made of edge-wound
aluminum ribbon. When centered in the
magnetic gap, the voice coil shall produce a
force of not less than 21.9 newtons (tesla-
ampere-meters) with a dc current of 1 ampere.
Performance specifications of a typical pro-
duction unit shall be as follows: measured
sensitivity (SPL at 1 m (3.3 ft) with 1-watt
input, 100- to 800-Hz pink noise) shall be at
least 96 dB. The half-space reference effi-
ciency shall be at least 3.0%. The usable fre-
quency response shall be 20 Hz to 2,000 Hz,
and the nominal impedance shall be 8 ohms.
The rated power for the loudspeaker shall
be 1,000 watts continuous program power.
The low-frequency transducer shall be the
Electro-Voice EVX-180B.
AES Specifications
EVX-180B specifications are in accordance
with the "AES Recommended Practice for
Specification of Components Used in Pro-
fessional Audio and Sound Reinforcement"
(AES2-1984; ANSI S4.26-1984).
Mounting
The EVX-180B may be front or rear
mounted against either surface of the mount-
ing flange and requires a 422-mm (16.6-in.)
diameter cutout and a 441-mm (17.38-in.)
bolt circle. Normal fasteners up to 6 mm (¼
in.) will fit through the eight holes in the
frame. Front mounting is simplest using the
optional SMH-1 speaker mounting hardware.
Electrical Connections
The EVX-180B is fitted with a pair of
chrome-plated, frame-mounted connectors
with color-coded ends. Electrical connection
is made by pushing down, inserting wire
completely through the rectangular slot and
releasing pressure. One conductor of #9
AWG stranded, #8 AWG solid, a pair of
twisted #15 AWG stranded or a pair of #14
AWG solid conductors will fit. A positive
electrical signal applied to the red (+) termi-
nal will displace the cone away from the
magnet, thus producing a positive acoustic
pressure.
Multiple-Driver Applications
When used in arrays and multiple-driver bass
boxes, the system Thiele-Small parameters
can be synthesized as follows. This data
should be used for multiple-driver configu-
rations.
Two Drivers:
f
:
28.1 Hz
s
Q
: 0.275
ts
V
: 835 liters (29.5 ft
3
)
as
Four Drivers:
f
:
26.9 Hz
s
Q
: 0.286
ts
V
: 1,671 liters (59.0 ft
as
Designers will find the following equation
useful in tuning their enclosures:
S
V
L
= ———————————— – K r
V
–4
3.7 x 10
V
f
B
Where:
L
= Length of vent in inches or thick
v
ness of baffle for hole in baffle
S
= Area of vent in square inches
V
V
= Volume of box in cubic feet
B
f
= Box tuning in Hz
B
r
= Radius of vent
K
= 1.7 for a hole in baffle, 1.5 for a
tube in inches
3
)
2
B
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