ELECTRO-VOICE XEG-3 Electronic Crossover User Manual

JXE0-3
ELECTRONIC CROSSOVER

SERVICE MANUAL

Specifications

CHANNEL CONFIGURATION —
Monaural three-way, switchable to monaural two-way

FILTER TYPE —
Fourth-order Linkwitz-Riley (24-d8-per-octave attenuation)

CROSSOVER FREQUENCIES, SWITCH SELECTABLE —
(See text for other possible frequencies)
Low-Mid: 60. 125, 180. 250, 500 and 800 Hz
Mid-High: 500, 800. 1250, 1800. 5000 and 8000 Hz

OUTPUT DELAYS —
Type: Fourth-order all-pass. continuously variable time constant. linear control scale
Rlange: Low: 6 us (“0”) lo 6 ms
Mid: 1 gs (“0”) to 1 ms
High: 0.3 ps (“0”) to 0.3 ms

INFRASONIC SPEAKER PROTECTION —
Fitter Type: Second-order Butlarworth (12-d6-per-octave slope)
Corner Frequencies: 16 or 32 Hz. provided by supplied HP16/32 ‘ plug-in module (sae ted for other traquencies)

EQUALIZATION FOR “STEP-DOWN” OPERATION OF TL BASS SPEAKER SYSTEMS —
Filter Type: Second-order underdamped (12-dB-per-octave rolloff below plus-6-dB peak-boost frequency)
Peek-Boost Frequencies: 29, 35. 45 and 60 Hz pronded by opbone! EB2935 and EB45/60 plug-in modules (see tax? for other frequencies)

EQUALIZATION OF MID- AND HIGH-FREQUENCY OUTPUTS, PROVIDED BY PLUGIN MODULE —
Normally Suppited: EQF module (for fiat electra! frequency response)
Optional Modules, for Fiat Acoustic Response of Compression
Drivers on Conetant-Directivity Horns: EQA. EQB. .
{see Table 1 for complete tet)

INPUT —
Type: Active differental
Maximum Level: +18 dBu
Impedance: 20,000 ohms
Common-Mode Range: + 24 V (nat of signal voltage)
Common-Mode Rejection Ratio, Typical: — 55 dB
Connector: Femaie 3-pin XA type

MAIN OUTPUTS —
Type: Floating ditferental (TR8-2 set of three isolabon transformers available; see text)
Maximum Level: +18 dBu
Impedance: 100 ohms
Minimum Loed Impedance for Full Output Level: 600 ohms
Protection: Safe for short crest or 225 volts dc
Connectore: Maie 3-pin XLR type

LOW-MIX (COMMON-BASS) OUTPUT —
Impedance: 1.800 ohms
Connector: RCA-type phono jack

GAIN —
Level Controis st Center Detent: Unity
Adjustment Range re Unity Gein, Continuously Variable: + 12 dB

FREQUENCY RESPONSE, SUM OF OUTPUTS, LEVEL CONTROLS AT CENTER DETENT, 2,000-OHM LOADS —
20-20,000 Hz 40.5 dB

TOTAL HARMONIC DISTORTION, 20-20,000 Hz —
Typical: 0.02%
Maximum: 0.1%

NOISE, EACH OUTPUT, CONTROLS FLAT, 20-20,000-Hz NOISE BANOWIOTH —
Typical: -90 dBu

CHANNEL CROSSTALK —
Typical: -78 dB

TRANSIENT PERFORMANCE —
Not limited by slew rate or power bandwidth under norma! operating condition, 20-20,000 Hz

LED LEVEL INDICATORS —
(Level-dependent brightness provides enhanced resolution)
Green: Input leve! above -20 dBu
Yellow: Input level above 0 dBu
Red: Input or any output level above +16 dBu

FRONT-PANEL CONTROLS —
Each Output: Gain, celay, polarity and channel mute

CHASSIS CONSTRUCTION —
Painted aluminum

COLORS —
Black with while graphics

MOUNTING —
Standard 19.n. rack panel, 1% in. hgh, 7 in. deep behind pane!

SUPPLIED ACCESSORIES —
HP 16/32 plug-in high-pass filter module for 16- or 32-Hz low-frequency protection; BMK blank plug-in modute for construction of custom modules: smoked acrylic security cover

OPTIONAL ACCESSORIES —
EQA, EQB.._. plug4n equalzaton modules for flat acoustc resporse of compression drivers on constart-cirectivay horns (see Table 1 for complete list):
TRB-2 set of three output isolation transformers

POWER REQUIREMENTS —
100-120 V ac, 60-60 Hz, 10 W
(also available for 80-110 and 220-240 V ac, 50-60 Hz)

OVERALL DIMENSIONS —
(see Figure 1)
44 mm (1.73 in.) high.
483 mm (19.0 in.) wide:
185 mm (7.28 in.) deep

NET WEIGHT —
3.1 kg (6.8 Ib)

SHIPPING WEIGHT:
3.8 kg (8.4 Ib)

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 18-0B-per­ octave rate of a third-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 XE-3 has a variable time-delay equalizer which is capable ot compensating tor 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 a plug-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) tor the LOW EQ and two EOF modules (flat response, no EO) 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 a level display for optimizing dynamic range; a level 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 TB-2 set of three) can be installed if desired.
The XE0-3 mounts in one EIA rack space and is supplied with a smoked acrylic front cover to prevent uninvited control adjustment. Figure 2 shows the XE0-3 block diagram

CONNECTIONS

Input and Outputs
The input connector is a 3-pin female XLR type; output connectors are 3-pin male XLRR type. Pins 2 and 3 are signal and each pin 1 is ground. This grounding arrange­ ment works well in most installations; pin 1 can be used as a ground reference or, if there is  another reference (a ground loop is formed), then the resistor allows pin 1 to follow the other ground reference. A solid chassis ground connection can be obtained at the connector shell.
The floating differential input and outputs can be unbalanced and referenced to other equipment, or they can be connected to balanced lines. If a true balanced source (or load) is needed, connect a 300-0hmn resistor from pin 2 to pin 1 and another 300-ohm  resistor from pin 3 to pin 1

Low Mix
The low-mix (or “common-bass”) connection is an RCA phono jack which aUows the low output to be mixed with the low output of another XE0-3 Or XEO-2. This can improve the performance of stereo or multi-channel installa­ tions by equaly distributing low- frequency energy among the low-frequency speakers. The low- mix connection also allows the use of a single 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 XE’s are interconnected in the low-mix mode, ary 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
A green LED on the front panel indicates when ac power in ON. The XE0-3 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 6 dB down at the selected frequency, compared to the midband response. See Figure 3.

The XE0-3 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 Bu, and the yellow LED lights when the signal reaches 0 dBu. 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 a level control with a ±12dB 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 a mute switch is pressed, the corresponding output will be shut off. These are useful for setup, calibration, and troubleshooting.

Time-Delay Controls
Each output on the XE0-3 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 filters with continuously variable  time constants (see Figures 4 and 5). Adjusting a delay control is acoustically equivalent to physically moving the corresponding speaker with respect to the others. The delays available may not always be sufficient to compensate for all physical location differences encountered. However, halt-wavelength shifts should nearly always be possible, thus eliminating the interference cancellations that can occur at crossover.

Normally only two delay controls are needed in a particular setup; the speaker with its acoustic center furthest from the listener should have its delay control left at “O.” There may be exceptions to this, such as when a certain unusual time response is desired.  The best way to adjust these controls is by measuring the direct-field on-axis frequency response using a plotter or a spectrum analyzer: reverse the polarity of the output to be adjusted, turn the delay control until the deepest possible response null occurs at the crossover frequency, then restore the correct polarity. The result will be optimum phase and frequency response through the crossover region. The delay controls can also be adjusted with just an oscillator, set at the crossover frequency, by listening for and  adjusting for the null, on axis and in the speaker system’s direct sound field. Switching to the correct polarity will then yield flat response. Set the level controls first, then set the delay controls.

Two-Way Operation
The XEQ3 can easily be set up for two-way operation by pressing one of the switches on the back panel. Which switch to press (LOW-MID or LOW-HIGH) depends on which crossover ferquency range is needed. The two corresponding outputs are then used. The  third output can be used also, if another speaker in a stack or cluster needs a different equalization module or control setting.
For example, by pressing LOW-MID and setting both crossover frequency switches to 500 Hz Or 800 Hz, the mid and high outputs have the same frequency range but separate controls and EO. The possible combinations are shown in Figure 6.

EQUALIZATION SECTIONS

Low-Frequency Equalization
The LOW EQ socket accepts plug-in modules for different types of higt-pass filters. The HP16/32 module (supplied) will provide a second-order Butterworth (maximally flat) response with a cutoff frequency of either 16 Hz or 32 Hz depending on which number  is right-side up when the module is installed. Other modules are available for “step­ down” operation (low-frequency extension) of Electro-Voice TL bass speaker systems. The EB29/35 and EB45/60 provide 6 dB of boost at the corresponding peak fre­ quencies,  for this purpose. Modules can be contructed for other frequencies and nigh-pass filter types see Custom Low-Frequency Modules section

Mid- and High-Frequency Equalization
The MID EQ and HIGH EQ circuits are identical to each other, but are in the mid and high signal paths, respectively.
These circuits will accurately equalize high-performance compression drivers used wth constant-directivity horns The proper EQ module for use with various EV horn-driver combinations is shown in Table 1

For applications requiring flat electrical frequency response, use EOF modules. The XE-3 is suppled with EOF modules installed in the MID EQ and HIGH EQ sockets.

DH1506
EQB| HR120, SM120
EQC| HR40, FIF160
EQD| HR9040A,HR4020A
ECM| HR6040A
EOF| FLAT
EQG| H1190| DH2012
EQH| HR120
EQJ| HR40, 111160
EQK| HR9040A, HR4020A
EOL| HR6040A
EOM| HP940| D111, DH1A
D112
EQN| HP1240
EQO| HP420, HP640
EQP| HP9040, HP4020
EQQ| HP6040
EQR| HP940| DH1A
EQS| HP1240
EQT| HP640
EQU| 111,4020,1t9040,4,6040
EQV| HP420

TABLE 1
Horn/Driver Equalization Modules

CUSTOM LOW-FREQUENCY MODULES

High-Pass Filters
If a low-frequency cutoff other than 16 Hz or 32 Hz is needed, a module can be constructed for other fre­quencies by soldering resistors into the supplied BMK blank module kit. Two resistors are needed tor each filter frequency. Note that each module can  accommodate two frequencies since there are two ways to plug t into the socket. One-quarter-watt film resistors having a resistance tolerance ot 1% r 2% are recommended, but in less critical applications, 5% resistors may suffice. Mi-type RN55D resistors are  easiest to use; however, conformally coated resistors may also be used.In the following formulas, RR, and R, are in ohms, and 1, is the corner frequency in Hz

For maximally extended low-frequency response, use R, =1 megohm and leave , out. The t will then be around 5 Hz to 10 Hz, depending on the load impedance

Step-Down EQ Modules
To make modules for step-down equalization of low-frequency speaker systems, use the following formulas The equalization circuit will produce a 6-dB pea at the frequency Ip, and a 12-0B-per-octave rollolt below the peak:

Module Construction

In addition to the Electro-Voice BMK blank module kit, the following items are required:

1. Two or four resistors, calculated from the formulas given above.
2. Low-wattage soldering iron with small chisel tip.
3. Electronic-grade solder, 63/37 0r 60/40 alloy, rosin core.
4. Flush-cutting diagonal cutters.
5. A spare 16-pin DIP socket.
6. Adhesive: epoxy. super glue or hot melt
7. Various hand tools, as needed.

Refer to the diagram in Figure 7:

1. Insert the DIP plug into the spare socket or use the one on the XE-3. This helps to keep the pins in alignment during soldering.
2. Locate pin 1 by the cut-off corner on the plug
3. Place and solder the resistors one by one and trim each lead close enough to the pin to allow later installation of the cap. If you are using conformally coated (dipped) resistors, be sure the leads are free of the coating material where they emerge from the resistor body. Be careful not to overheat the pins, or the plastic base will melt.
4. Check all connections and resistor values.
5. Attach the cap with glue.
6. Label the module.

NON-STANDARD CROSSOVER FREQUENCIES

The XE0-3 can be modified to provide crossover frequencies other than the six frequencies available at each switch. This is easily done (only resistors and a phillips screwdriver are reeded) if the new crossover frequency is between 80 Hz and 800 Hz for the low- mid switch and between 500 Hz and 8,000 Hz for the mid-high switch.
Four Ve-watt, 1% resistors are needed for each filter switch.
For a crossover frequency t_, the following resistor value is needed:

1. Low-mid filter:
2. Mid-high filter:
   

OUTPUT TRANSFORMERS

The outputs of the XEQ-3 can be transformer coupled by adding the optional TRB-2 set of three transformers to the circuit board. This should be done by a qualified service technician. Remove two screws from each side and the back, and lift off the top cover.  Then remove the five screws holding the circuit board to the chassis, and four hex screws from the front panel. The circuit board, with the front panel attached, can then be removed from the chassis.
Thre are fourteen jumpers which must be removed from the board so that the three transformers will have the proper drive, feedback, and output connections. The jumpers are labeled JP1 through JP14. See Figure 9. To remove a jumper, clip the lead at each end  and remove the center section.
The transformer lead layout is asymmetrical, so verify the orientation of the transformer leads with the holes in the circuit board before installing. Solder all connections on the foil side of the board, Reassemble the XE-3 in reverse order from the description  above.

Figures

LINK WITZ-RILEY FILTER ADVANTAGES

All contemporary crossover designs maintain predictable acoustic summing in the horizontal plane with vertically aligned system configurations. However, in the vertical plane, common Butterworth designs exhibit a phenomenon termed “lobing error”caused by  the 90-degree phase shift of outputs and the 3-dB attenuation at crossover. To explore the implications of lobing error, the following text examines the radiation patterns of systems using a Butterworth filter (Figure 10) and a Linkwitz-Riley filter (Figure 11)

In Figure 10, the cancellation axes result from the same acoustic signal of two physically dip/aced sources arriving out of phase at discrete locations. Consider a typical system with a horn/driver combination in vertical alignment with a low-frequency system. For  locations above or below the system axis, acoustic signals at crossover frequency will arrive from the horn and woofer at different times (due to the path-length differences), resulting in a “phase cancellation” at discrete locations The peaking axis represents  the discrete locations where the two transducers are exactly in phse and combine to produce a +-3-01B peak relative to the on-axis level. As phase cancellation is frequency dependent, changing the crossover frequency will alter the axis orientation
Linkwittz-Riley filters are termed “zero lobing error” because the unvoidable cancellation axes are placed symmetrically above and below the system axis. Also, the system on-axis response is “flat” with no ott-axis response peaks.
In Figure 11, the Linkwitz-Riley filter does not eliminate the cancellation axis; again, this is purely a function of two displaced sources reproducing a common frequency.
However, from a design standpoint, the lobes are now placed in a much more manageable position-consider a ypical system orientation with respect to a seating area Commonly, the system is aimed near the center of the

seating bank. From Figure 10, it is obvious that a seating section below the system will experience a “hot spot” produced by the peaking lobe of a system using a Butterworth-design crossover filter Also, a seating area above the system axis will experience a  “dropout”caused by the interference along the upper cancellation axis. In contrast, consider the same conditions using a Linkwtz­ Riley crossover filter.

With Linkwitz-Riley filter characteristics, there is no peaking axis and, theretore. no “hot spots”referenced to the system axis. In the above example. the Linkwitz-Riley cancellation axes are locate at ± 30° relative to the system As the vertical coverage pattern of  common high frequency horns is 40° (±20°), the cancellation axes are located beyond the designed coverage area in single horn/driver systems. Recall from Figure 10 that one cancellation axis tor a Butterworth fitter is located within the coverage pattern of  typical horns.

From the above examples and illustrations, it clear that Linkwitz-Riley fitter characteristics otter the sound-system designer distinct advantages, as opposed to Butterworth designs, for electronic crossovers. In summary, Linkwtz­ Riley filters produce no otf-axis  response peaks and place the inevitable cancellation axes symmetrically above and below the system axis tor smoother overall frequency response in the crossover region.

A more detailed and graphic treatment of the subject is available in a number of technical articles, including.

1. SH Linkwtz, “Active Crossover Networks for Noncoincident Drivers,” J. Audio Eng. Soc., vol. 24, pp. 2-8 (1976 January/February)
2. SP. Lipshitz and J. Vanderkooy, “A Family of Linear­ Phase Crossover Networks of High Slope Derived by Time Delay,”J. Audio Eng SOC., vol. 31 pp. 2-20
   (1983 January/February)

PC Board

Schematic

Schematic

Schematic

Parts List/Notes

References

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