Rane SAC 22 2003 version - Manual (Page 6)

Manual-4
OPERATING INSTRUCTIONS
Selecting Crossover Frequencies
Most speaker manufacturers supply low and/or high frequency
cut-off points for each driver, especially if these are supplied in
a system. These cut-off frequencies are based on each driver’s
performance, with a certain safety margin to accommodate more
gentle filter roll-offs.
The SAC 22 utilizes a 31-position precision DC control volt-
age potentiometer to select the LOW/HIGH frequency point.
This crossover circuit design assures consistent accuracy from
channel-to-channel and unit-to-unit. This is a distinct advantage
over continuously variable designs using ganged potentiometers
which can yield large variations in channel-to-channel matching.
Even with 31 choices it is possible that the exact recommended
Crossover frequency may not fall on one of the detents on the
selector. Not to panic, for drivers have their own gradual rolloffs
and tolerance variations. Just pick the closest one. When in
doubt, choose the higher frequency setting.
For best overall system results, try to choose the speaker
components so that each operates well within its recommended
limits. This provides valuable leeway so that crossover points
may be adjusted in order to fine-tune the system. This also yields
higher system reliability. If at all possible, always use some kind
of realtime analyzer to tune your crossover, and then fine-tune
each system with an equalizer. Keep reading for further align-
ment details.
Setting the Output Level Controls
The INPUT LEVEL is an overall system sensitivity adjustment.
Use this control to decrease the overall sensitivity of the entire
sound system, including the mono subwoofer if you are using
one. You will generally want to start with this control in the full
clockwise (or 10) position.
The LOW LEVEL, HIGH LEVEL and MONO SUB OUT-
PUT LEVEL controls allow you to compensate for sensitivity
variations in amplifiers and drivers. Do not use these to adjust
overall system sensitivity unless you plan to re-align the system
afterward. With these set to the 0 dB mark and the INPUT
LEVEL set to 10, the crossover yields no level change from input
to output. This is the best gain structure and provides the best
signal-to-noise performance.
Crossover Philosophy
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 re-
sponse 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 real-
time analyzer and pink noise source, 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 response
for 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.
Regardless of which school you profess, the absolute impor-
tance and effectiveness of some kind of realtime analyzer in your
system cannot be overstressed! An analyzer saves tremendous
amounts of time and provides 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 today’s cost-effective analyzers—you’ll wonder how you man-
aged at all without one.
Setting the Mono Sub Output Level
Begin with the MONO SUB OUTPUT LEVEL control set at
MAX. The LOW LEVEL control has no affect on the MONO
SUB OUTPUT. Make subwoofer level changes with either the
MONO SUB OUTPUT LEVEL or with the amplifier level
control. If you are using the MONO SUB OUTPUT instead of
the LOW OUTPUTS, be sure the 100 Hz FILTER is switched
OUT.