Description
The Electro-Voice EQ-131 is a boost and cut
1
/
3
-octave graphic equalizer whose primary
use is for tuning the overall frequency re-
sponse of a sound reinforcement system, both
to increase gain-before-feedback and to com-
pensate for the deficiencies in the acoustic
environment and the sound system.
Features
The variable-Q active filter sets used in the
EQ-131 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. The fil-
ter response is designed to affect a
1
/
3
-octave
range. Many graphic equalizer designs have
filters in which the Q, or sharpness of the
filter, varies depending on the amount of
boost or cut used. In most cases, the Q is
very low when small corrections are set and
the affected frequency range goes beyond
even the adjacent filter controls. In these
designs, when a large amount of boost or cut
is used, the filter skirt spreads out and influ-
ences a larger frequency range so that adja-
cent controls must be readjusted.
Each of the 31
1
/
3
-octave filters provides 12
dB of boost or cut at ISO frequencies 20
through 20,000 Hz. The faders have a posi-
tive detent in the center, flat-response posi-
tion.
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. 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 dis-
torts the output in the reproduced frequency
range and, most seriously, could damage the
speaker from excessive cone motion or “bot-
toming.”
The range select switch allows selection of
either 6 or 12 dB of boost and cut. The 6-dB
range will allow more control selectivity
while the 12-dB range allows for greater
range of adjustment.
The EQ-131 has a 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.
Architects’ and
Engineers’ Specifications
The equalizer shall have 31 filters centered
at the ISO standard
1
/
3
-octave 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 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 input and output of the equalizer shall
be accessible via 3-pin XLR-type and
1
/
4
-inch
EQ-131
Mono One-Third Octave
Graphic Equalizer
• 31 1/3-octave filters 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
• Space saving single rack space
chassis with internal power
supply with IEC connector
