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Description
The Electro-Voice EQ-231 is a boost-and-
cut stereo
1
/
3
-octave graphic equalizer whose
primary use is for tuning the overall fre-
quency response of a sound reinforcement
system, both to increase gain-before-feed-
back and to compensate for the deficiencies
in the acoustic environment and the sound
system.
Features
The variable-Q active filter sets used in the
EQ-231 allow effective equalization with
few problematic side effects. As Figure 1 il-
lustrates, the filter characteristics vary with
the amount of boost or cut used. At low con-
trol settings, the filter Q is very wide. As the
control is boosted or cut, the filter Q nar-
rows so that there is minimum interaction
between adjacent frequency bands.
Each of the 31
1
/
3
-octave filters per channel
provides 12 dB of boost or cut at ISO fre-
quencies 20 through 20,000 Hz (see Figure
2). The faders have a positive detent in the
center, flat-response position.
The gain control also has a center detent at
unity gain. It should be adjusted so that the
adjacent peak LED rarely or never lights. This
will help achieve maximum possible signal-
to-noise ratio.
The infrasonic low-cut filter, with a 43-Hz
corner frequency and a slope of 18 dB per
octave, is engaged by the front-panel Lo-Cut
switch (see Figure 3). For most applications,
the filter should be engaged. Most profes-
sional speaker systems have little output be-
low 45 Hz. At best, driving them in this range
wastes amplifier power, and can result in
excessive, ultra-low-frequency cone motion
which distorts the output in the reproduced
frequency range and, most seriously, could
damage the speaker from excessive cone
motion or “bottoming.”
The range select switch allows selection of
either 6 or 12 dB of boost and cut on either
channel. The 6-dB range will allow more
control selectivity while the 12-dB range al-
lows for greater range of adjustment.
The EQ-231 has an IEC connector to allow
compatibility with ac connections anywhere.
The integral fuseholder also doubles as the
voltage selector to allow for operation any-
where in the world.
Figure 5 shows front and rear panel details.
Architects’ and
Engineers’ Specifications
The equalizer shall have 31 filters for each
channel centered at the ISO standard
1
/
3
-oc-
tave frequencies between 20 and 20,000 Hz.
The filters shall provide either 6 or 12 dB of
boost or cut and be set by 22.5-mm linear
controls. The front panel shall have the fol-
lowing controls: a gain control that is con-
tinuously variable from -12 dB to +12 dB
from unity gain; a high-pass filter with a
slope of 18 dB per octave and a corner fre-
quency of 43 Hz; a range switch to select
either 6 or 12 dB of boost or cut from the
filters; an EQ-on switch to put the filters in
the signal path and an on/off switch.
The rear panel shall have the input and out-
put connectors, a ground-lift switch and a
IEC connector with an integral fuse holder
that allows voltage selection by the way it is
inserted.
The inputs and outputs of the equalizer shall
be accessible via 3-pin XLR-type and
1
/
4
-inch
TRS phone jacks located on the rear of the
unit. The input shall be actively balanced.
The output shall be balanced on the 3-pin
XLR-type plug.
EQ-231
Stereo One-Third Octave
Graphic Equalizer
• 31 1/3-octave filters on each
channel for effective sound
system equalization
• Switchable infrasonic filter and
ground-lift
• Selectable (6 or 12 dB) range of
boost/cut
• Active-balanced 3-pin XLR-type
and TRS 1/4-inch inputs
• Two rack space chassis with
internal power supply with IEC
connector