Electro-Voice EQ-231 User Manual 2

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

Description

The Electro-Voice EQ-231 is a boost-and­cut stereo
primary use is for tuning the overall fre­quency response of a sound reinforcement
system, both to increase gain-before-feed­back 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 il­lustrates, the filter characteristics vary with
the amount of boost or cut used. At low con­trol settings, the filter Q is very wide. As the
control is boosted or cut, the filter Q nar­rows so that there is minimum interaction
between adjacent frequency bands.

Each of the 31
provides 12 dB of boost or cut at ISO fre­quencies 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

1

/3-octave graphic equalizer whose

1

/3-octave filters per channel

adjacent peak LED rarely or never lights. This
will help achieve maximum possible signal­to-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 profes­sional speaker systems have little output be­low 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 al­lows 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 any­where 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
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 fol­lowing controls: a gain control that is con­tinuously 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 fre­quency 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 out­put 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
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.

1

/3-oc-

1

/4-inch

EQ-231/Graphic Equalizer

The equalizer shall meet or exceed the fol­lowing performance specifications: fre­quency response at unity gain, …1 dB 20 ­20,000 Hz; total harmonic distortion less than

0.01%, 20 - 20,000 Hz at 0 dBu; a noise level
of less than -97 dBu; gain of ±6 dB or ±12
dB; balanced-input impedance of 44,000
ohms; output impedance of 120 ohms; a
maximum input level of +20 dBu at unity
gain; a maximum output level of 20 dBu into
loads greater than or equal to 600 ohms.

The equalizer shall operate on 120 V/240 V
ac, 50/60 Hz, and consume less than 18 watts.
The unit shall be operable over the tempera-

EQ-231/Graphic Equalizer

ture range as high as 50 degrees Centigrade
or 122 degrees Fahrenheit. The chassis shall
be steel with a gray front panel and black
top, bottom, sides and back with white no­menclature. The chassis shall occupy one
rack space in a standard 19-inch rack (height:

3.46 inches; depth: 9.24 inches; width: 19
inches). The weight shall be 8.8 lb (4.0 kg).
The equalizer shall have a three-year parts
and labor warranty. The equalizer shall be
the Electro-Voice EQ-231.

Limited Warranty

Electro-Voice products are guaranteed
against malfunction due to defects in mate­rials or workmanship for a specified period,
as noted in the individual product-line

statement(s) below, or in the individual prod­uct data sheet or owner’s manual, beginning
with the date of original purchase. If such
malfunction occurs during the specified pe­riod, the product will be repaired or replaced
(at our option) without charge. The product
will be returned to the customer prepaid. Ex-
clusions and Limitations: The Limited
W arranty does not apply to: (a) exterior fin­ish or appearance; (b) certain specific items
described in the individual product-line
statement(s) below, or in the individual prod­uct data sheet or owner’s manual; (c) mal­function resulting from use or operation of
the product other than as specified in the
product data sheet or owner’s manual; (d)
malfunction resulting from misuse or abuse
of the product; or (e) malfunction occurring
at any time after repairs have been made to
the product by anyone other than Electro­Voice Service or any of its authorized ser­vice representatives. Obtaining Warranty
Service: To obtain warranty service, a cus­tomer must deliver the product, prepaid, to
Electro-Voice Service or any of its autho­rized service representatives together with
proof of purchase of the product in the form
of a bill of sale or receipted invoice. A list of
authorized service representatives is avail­able from Electro-V oice Service at 600 Cecil
Street, Buchanan, MI 49107 (800/234-6831

or FAX [phone]). Incidental and
Consequential Damages Excluded: Prod­uct repair or replacement and return to the
customer are the only remedies provided to
the customer. Electro-Voice shall not be li­able for any incidental or consequential dam­ages including, without limitation, injury to
persons or property or loss of use. Some
states do not allow the exclusion or limita­tion of incidental or consequential damages
so the above limitation or exclusion may not
apply to you. Other Rights: This warranty
gives you specific legal rights, and you may
also have other rights which vary from state
to state. Electro-V oice Electronics are guar­anteed against malfunction due to defects in
materials or workmanship for a period of
three (3) years from the date of original pur­chase. Additional details are included in the
Uniform Limited Warranty statement.

For warranty repair or service informa­tion, contact the service repair department
at: 616/695-6831 or 800/685-2606.

For technical assistance, contact Technical
Support at 800/234-6831 or 616/695-6831,
M-F, 8:00 a.m. to 5:00 p.m. Eastern Stan­dard Time.

Specifications subject to change without
notice.

FIGURE 1 — Filter Response at
Different Slider Positions Showing Q of
Filter Changing.

OUTPUT IN dB

2

FIGURE 2 — Filter Response at ±12-dB
Slider Positions

OUTPUT IN dB