Rane AC 23B (2003 version) - Manual (Page 17)

Manual-
Constant Directivity Horn EQ Mod
Constant Directivity (or CD) horns need additional equal-
ization to help cover the same area a long throw horn can cover.
Additional circuitry has been added to the AC 23B for additional
equalization of the High Frequency outputs for the CD Horns.
This modification should only be attempted by an experienced
technician.
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 frequency 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 the table
below to determine the correct value capacitor to install in the
AC 23B to correct for this high frequency roll off.
STEP BY STEP PROCEDURE
This procedure is for CD horn EQ on the High output in
Stereo 3-Way mode. For a Mono 4- or 5-Way system with a CD
horn on the high output, only place C16 in Channel 2.
1. Remove the top and bottom covers of the AC 23B.
2. Locate the positions for C15 and C16 on the Schematics page
3 and on the circuit board. See Assembly Diagram.
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.
4. Replace the top and bottom covers.
3 dB Down Frequency Capacitor
2.0 kHz .0068 µf
2.5 kHz .0056 µf
3.0 kHz .0047 µf
3.7 kHz .0039 µf
4.0 kHz .0036 µf
5.0 kHz .0030 µf
6.0 kHz .0024 µf
106001
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Setting Levels Using an SPL
Meter & Pink Noise Generator
The MUTE switches on the AC 23B make using an SPL
meter an easy and relatively accurate means of tuning a system.
The Rane RA 30 has everything you need, an SPL meter and a
pink noise source. If you can’t get one of those right now, obtain
a good SPL meter and a pink noise generator from a local elec-
tronics store. You may also use a sweep or tone generator in place
of a pink noise source. If so, be sure to look at several different
tones within each crossover section to get a good average driver
response.
1. Run pink noise into the crossover Inputs (through the mixer
or directly, as is convenient).
2. Make sure all crossover output LEVEL controls 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 re-
mains 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 switches are present.
4. Slowly turn the LOW LEVEL of the crossover up until there
is a healthy rumble coming from the bass speakers (For this
example the 3-Way configuration is used—the same proce-
dure applies to all configurations, starting with the lowest
frequency and ending with the highest). Adjust the SPL meter
and/or crossover output until you get a 0 dB 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 0dB adjust-
ment 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 pink noise
is heard from the mid frequency speakers. Without changing
any settings on the SPL meter, adjust the MID LEVEL 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 read-
ing (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 level control). Now
go back and re-adjust the previous crossover level controls, turn-
ing 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 crossover, 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 controls and leave
the output level controls unchanged.