XEQ-3 SERVICE MANUAL Description, Connections, Control Functions
DESCRIPTION
The XEQ-3 electronic crossover/equalizer is intended
primarily for high-quality sound systems which require
precise crossover filtering and accurate speaker system
compensation for optimum frequency and time response.
The XEQ-3 incorporates fourth-order Linkwitz-Riley
frequency-dividing networks which have two unique advan-
tages over the third-order Butterworth networks often used
in high-performance professional sound systems. First, a
fourth-order network offers an out-of-passband attenuation
rate of 24 dB per octave, greater than the 18-dB-per-
octave rate of athird-order network. This provides better
protection of drivers from energy outside their frequency
range, important in some applications. Second, the
Linkwitz-Riley network has "zero lobing error,” for
smoother overall frequency response in the crossover
region. This concept is treated in more detail in the
section below.
Each output of the XEQ-3 has avariable time-delay
equalizer which is capable of compensating for different
speaker mounting positions and phase responses, so that
proper acoustic summing will occur at the crossover
frequencies. Each output also has an EQ section controlled
by aplug-in module. The LOW EQ can be used as an
infrasonic filter or for “step-down" operation of TL bass
speaker systems. The MID EQ and HIGH EQ are designed
to provide constant-directivity horn and driver equalization
when used with the appropriate module. The XEQ-3 is
supplied with an HP16/32 module (infrasonic filter at 16 or
32 Hz) for the LOW EQ and two EOF modules (flat
response, no EQ) for the MID EQ and HIGH EQ sections.
Other modules can be ordered from Electro-Voice or
custom built using the supplied BMK blank module.
Other features include alevel display for optimizing
dynamic range; alevel control, polarity reverse switch and
mute switch for each output; switches which allow two-way
crossover operation; and floating differential input and
outputs. Output transformers (Electro-Voice TRB-2 set of
three) can be installed if desired.
The XEQ-3 mounts in one EIA rack space and is
supplied with asmoked acrylic front cover to prevent
uninvited control adjustment. Figure 2shows the XEQ-3
block diagram.
CONNECTIONS
Input and Outputs
The input connector is a3-pin female XLR type; output
connectors are 3-pin male XLR type. Pins 2and 3are
signal and each pin 1is ground. This grounding arrange-
ment works well in most installations; pin 1can be used as
aground reference or, if there is another reference (a
ground loop is formed), then the resistor allows pin 1to
follow the other ground reference. Asolid chassis ground
connection can be obtained at the connector shell.
Low Mix
The low-mix (or "common-bass") connection is an RCA
phono jack which allows the low output to be mixed with
the low output of another XEQ-3 or XEQ-2. This can
improve the performance of stereo or multi-channel installa-
tions by equally distributing low-frequency energy among
the low-frequency speakers. The low-mix connection also
allows the use of asingle amplifier/ subwoofer combination
in stereo or multi-channel systems.
Any number of crossovers may be used this way by
connecting their low-mix jacks together. When XEQ's are
Interconnected in the low-mix mode, any or all of the low-
frequency outputs may be used. These outputs will have a
common signal but their individual level, polarity, mute and
delay controls will still function independently,
Power
Agreen LED on the front panel indicates when ac power
in ON. The XEQ-3 may be left on indefinitely or externally
switched with other equipment.
CONTROL FUNCTIONS
Crossover Frequency
The six-position rotary switches select the frequencies for
the low-mid and mid-high crossover filters. The correspond-
ing outputs will be 6dB down at the selected frequency,
compared to the midband response. See Figure 3.
The XEQ-3 can be modified to provide other frequencies
—see Non-Standard Crossover Frequencies section.
Input Level Indicator
The level of the input signal to the XEQ-3 is monitored with
three LED's. The green LED indicates signal above
-20 dBu, and the yellow LED lights when the signal
reaches 0dBu. The red LED lights if the input or any
output exceeds +16 dBu. In normal operation, the yellow
LED should light much of the time (indicating normal signal
level) but the red LED should not light.
Level Controls
Each of the three outputs has alevel control with a
±12 dB range. The center detent position is unity gain.
These controls are intended for fine-tuning the system
response; large differences in speaker output should be
approximately compensated with the power amplifier’s
attenuators and then accurate level matching can be
achieved with the XEQ-3 level controls.
Polarity Reverse Switches
These switches will reverse the polarity of the correspond-
ing output. These are used primarily to assist adjustment of
the delay control.
Mute Switches
When amute switch is pressed, the corresponding output
will be shut off. These are useful for setup, calibration, and
troubleshooting.
The floating differential input and outputs can be unbalanced
and referenced to other equipment, or they can be
connected to balanced lines. If atrue balanced source (or
load) is needed, connect a300-ohm resistor from pin 2to
pin 1and another 300-ohm resistor from pin 3to pin 1
.
Time-Delay Controls
Each output on the XEQ-3 has time-delay control which
allows compensation for the time- and phase-response
differences which exist in almost all practical multi-way
speaker setups. The delay sections are four-pole, all-pass
three
