Rane AC 22B (1998 version) - Manual (Page 13)

Manual-13
of a pink noise source. If so, be sure to look at several
different tones within each crossover section to get a good
average of driver response.
1. Run pink noise into the crossover Inputs (through the mixer
or directly, as is convenient).
2. Make sure all crossover LEVEL(s) are turned all the way
down and all amplifier level controls are at least half way
up to start with.
3. Turn the crossover MASTER LEVEL(s) half way up. Place
the SPL meter at least 15 feet from the speaker stack and
about chest high. Once positioned, make sure that the SPL
meter remains in the exact same location for the rest of the
procedure. Minimize all background noise (fans, air
conditioners, traffic, wild animals, etc.) to get accurate
readings. Set the SPL meter to “C-weighting”, “slow” if
those switches are present.
4. Slowly turn the LOW LEVEL up until there is a healthy
rumble coming from the bass speakers (For this example
the 3-Way mode is used—the same procedure applies to all
configurations, starting with the lowest frequency and
ending with the highest). Adjust the SPL meter and/or
LOW LEVEL until you get a 0dB reading on the meter.
After this point do not change the controls on the SPL
meter.
5. While leaving the LOW LEVEL control at the 0 dB
adjustment just obtained, press the LOW MUTE switch on
the crossover so that the pink noise disappears from the
bass speakers (revel in the silence...).
6. Now slowly turn up the MID LEVEL control so that pink
noise is heard from the mid frequency speakers. Without
changing any settings on the SPL meter, adjust the cross-
over MID LEVEL control until you obtain a 0 dB reading
on the SPL meter. Now the low and mid speakers are set at
the same level.
7. Now press the MID MUTE switch on the crossover so that
the pink noise again disappears.
8. Repeat this process for each frequency section of the
crossover, ending with the highest frequency. NOTE: It is
possible that you may turn one of the frequency section
output LEVEL controls all the way up and still not have
enough volume for a 0 dB reading (as determined by
previous section levels). This is probably due to different
sensitivities of amps, speakers and other level controls in
the system. When this happens, re-set the SPL meter so that
it reads 0 dB on this frequency section (you may have to
“down range” the meter and re-adjust the crossover
MASTER LEVEL control). Now go back and re-adjust the
previous crossover LEVEL controls, turning these down to
get a 0 dB reading on the meter.
9. Once the HIGH LEVEL control is set for 0 dB on the
meter, disengage all of the MUTE switches on the cross-
over, and check that noise is emitting from all the speaker
components. The crossover should now be aligned. Make
any overall level adjustments with the MASTER LEVEL
level controls and leave the output LEVEL controls
unchanged.
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103034
Constant Directivity Horn
Equalization Modification
Constant Directivity (or CD) horns need additional
equalization to help cover the same area a long throw horn
can cover. Additional circuitry has been added to the AC 22B
layout for the additional equalization of the High Frequency
outputs for CD horns. This modification should only be
attempted by an experienced technician who is adept at
soldering.
It is important to know the 3 dB down point of the CD
driver's frequency response. The manufacturer of your driver
should be able to supply you with a chart showing a fre-
quency response curve. Find the point where the high end
starts to roll off, and look for the point on the chart that is 3
dB down from that point (toward the right, as the higher
frequencies roll off). Find the frequency at the bottom of the
chart of this point — an approximate is fine, you don't have to
be exact. Find the closest frequency in Figure 6 to determine
the correct value capacitor to install in the AC 22B to correct
for this high frequency roll off.
STEP BY STEP PROCEDURE
The following procedure is for Stereo 2-Way. For a Mono
3-Way system with a CD horn on the high output, only place
C212 in Channel 2.
1. Remove the top and bottom covers of the AC 22B.
2. Locate the positions for C112 and C212 on the following
page and on the circuit board. C112 (for Channel 1) is
located near the middle of the board. C212 (for Channel 2)
is located near the middle and right edge of the board.
3. Clean the solder pad on the underside of the board so that
the appropriate capacitor can be inserted. Install the
capacitor, and solder the leads from the underside using
fresh solder. Clip the excess leads.
3 dB Down
Frequency
Capacitor
2.0 kHz .0015 µf
2.5 kHz .0012 µf
3.0 kHz .001 µf
3.7 kHz 820 pf
4.0 kHz 750 pf
5.0 kHz 620 pf
6.4 kHz 470 pf