Rane AC 23B (2003 version) - Manual (Page 16)

Manual-
Setting the Output Level Controls
Choosing the crossover frequencies was the easy part. Now
it gets real fun. The idea is to set the output Level controls on
the crossover so that the entire speaker system has a uniform,
flat response. Unfortunately, the room in which the speakers
are placed has a habit of always getting into the act, so things
get messy. As a result there seems to be two schools of thought
regarding the use of active crossovers.
The Set‑lt‑Once‑And‑Glue‑lt School
The philosophy here is to use the crossover to flatten system
response as much as possible without room acoustics involved.
This means setting up the system outside (unless you happen to
have a very large anechoic chamber handy) and with the aid of
a realtime analyzer and pink noise source (ala RA 30), adjust all
of the crossover outputs so that the system is as flat as possible.
Once the system is tuned, the crossover is then locked behind
a security cover (posted guard is optional) and never again
touched. It is then the job of the system equalizer(s) to normalize
or flatten the system to each different room.
The Fix‑lt‑With‑The‑Crossover School
Here the crossover knobs get a good workout, for the cross-
over is used at each location to help flatten the system along with
the equalizer. Some even maintain that a good active crossover
can work alone like a parametric equalizer in the hands of an ex-
pert. This does require experience, skill, and the right equipment
to back it up (not to mention a licensed set of ears).
Regardless of which school you profess, the absolute impor-
tance and effectiveness of some kind of realtime analyzer in your
system cannot be overstressed! No, this is not a callous plug for
our other products; analyzers in general have come a long way.
They’re out of the lab (i.e. closet) and into the hands of every
smart working musician and sound technician. An analyzer will
save tremendous amounts of time and provide the absolute con-
sistency, accuracy, and plain old good sound that very few ears
on this earth can deliver. They are affordable, easy to use and
amazingly effective. You owe it to yourself and your audience to
at least look into one of these analyzers — you’ll wonder how
you managed at all without one.
Whether by analyzer or ear, here are a few recommended
methods of setting the crossover output Levels.
Setting Levels Using a Realtime
Analyzer
NOTE: If you are running two Channels, tune up only one
Channel at a time.
1. Set all LEVEL controls on the crossover to minimum; leave
Delay and Frequency controls as set previously.
2. Place the analyzer microphone at least 15 feet away from the
speaker stack, on axis (dead ahead) and about chest level.
Minimize any background noise (fans, air conditioners, traf-
fic, etc.) that could affect the readings.
3. Run pink noise through the system, either through a mixer
channel or directly into the crossover. Turn all amplifier con-
trols at least half way up.
4. We will use the 3-Way mode here as an example—the
procedure applies to all configurations. Turn up the INPUT
LEVEL control(s) on the crossover about half way.
5. Slowly turn up the LOW LEVEL control on the crossover, un-
til you hear a healthy level of noise through the low frequency
drivers (it should sound like rumble at this point).
6. Adjust the display controls on the analyzer so that it shows the
greatest number of 0 dB LED’s (green on Rane equipment)
below the crossover point.
7. Now slowly turn up the MID LEVEL on the crossover until
the display shows the same output level average as the Low
frequency section.
8. Repeat this procedure for all crossover frequency sections,
lowest to highest, so that the end result is as flat response as
possible on the analyzer display.
IMPORTANT: Compression driver or horn roll-off, bass
roll-off, and room acoustics usually cannot be corrected by the
crossover. If you are using constant directivity horns, see page 18.
If, for example, you are adjusting the High frequency controls and
observe a decline in frequency response somewhat above the crossover
point, then set the crossover LEVEL control for equal display level
near the crossover point and leave it there. Then use an equalizer or
bank of tweeters to correct the roll-off problem. If you are tuning the
system in a room, the room acoustics will greatly influence the system
response, as shown by the analyzer.
Check the system response on an analyzer at several other
locations and adjust the crossover as necessary to reach a fixed
compromise setting if desired. If you plan to use the analyzer
only once to set the crossover, set up the speaker system in a qui-
et place outside or in a very large concert theater, and run pink
noise at low levels with closer microphone placement to keep the
room acoustics out of the picture as much as possible.