Manual-12
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 27),
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 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
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
importance 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 consistency, 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 recom-
mended 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
crossover 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 condition-
ers, traffic, 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
controls 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
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 section.
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
Constant Directivity Horn Modification section on page 14.
If, for example, you are adjusting the HIGH FREQUENCY
control and observe a decline in frequency response some-
what 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 quiet place outside or in a very large concert
theater, and run pink noise at low levels with closer micro-
phone placement to keep the room acoustics out of the picture
as much as possible.
