Manual-16
Setting Levels Using an SPL
Meter & Pink Noise Generator
The MUTE switches on the AC 23 make using an SPL
meter an easy and relatively accurate means of tuning a
system. First, obtain a good SPL meter from a local electron-
ics or hi-fi store. Second, and perhaps a little trickier, get a
hold of a pink noise generator—again try electronics stores.
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 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
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 procedure 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
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 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
controls and leave the output level controls unchanged.
Fig. 4 Configuration with Long
Throw Horn
Fig. 5 Configuration with Constant
Directivity Horn
Time Delay Transplant
Modification
We have added modification jumpers to the AC 23. These
jumpers permit the transplanting of the Delay circuits from
one output to another. As the units are shipped, the Delay
circuit is not installed on the High Frequency outputs. When
the AC 23 was first designed, long throw horns were more
common than Constant Directivity horns (CD horns). The
long throw horn's diaphragm was the farthest sound emitter
from the front of the speaker enclosure, (see Fig. 4) so no
delay was needed. The mid frequency and low frequency
drivers were always in front of the high frequency drivers,
therefore, the mid and low frequency drivers needed the
Delay circuits for proper time alignment.
Now, with the use of CD horns becoming more common,
