Rane AC 22B (2003 version) - Manual (Page 13)

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 pos-
sible 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 crossover is used at each loca-
tion 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 expert. 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 by ear, here are a few recommended
methods of setting the crossover Output Levels.
Setting Levels With a Realtime
Analyzer
NOTE: If you are running two Channels, tune up only one
Channel at a time.
1. Set all LEVEL controls to minimum; leave Delay and cross-
over 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 pro-
cedure applies to all configurations. Turn up the MASTER
LEVEL control about half way.
5. Slowly turn up the LOW LEVEL control until you hear a
healthy level of noise through the low frequency drivers (it
should sound like rumble).
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 frequency.
7. Now slowly turn up the MID LEVEL control until the display
shows the same output level average as the low frequency sec-
tion.
8. Repeat this procedure for all crossover frequency sections,
so that the end result is as flat as possible a response on the
analyzer display.
IMPORTANT: Compression driver or horn roll-off, bass
roll-off, and room acoustic usually cannot be corrected by the
crossover. If you are using constant directivity horns, see the Con-
stant Directivity Horn Modification section on page 12. If, for
example, you are adjusting the HIGH FREQUENCY control and
observe a decline in frequency response somewhat above the crossover
point, then set the HIGH 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 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.