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14
Using the S curve 215 to Remove Feedback
One of the most important applications for the S curve 215 is removing feedback from an
onstage monitor system. This procedure is sometimes called “ringing out,” since feedback
usually begins with a slight ringing sound at the resonant frequencies where the loop
between microphone and speaker is loudest. The advanced Constant Q circuitry used by
both models ensures that adjacent program frequencies which may not be causing any prob-
lems are unaffected even when attenuating problem frequencies by their maximum amount.
To ring out a monitor system, start by setting up the stage exactly as it will be used during
performance, preferably with the performers themselves standing in front of the mics they
will be using (this is important since the physical placement of objects—or people—on the
stage can affect the generation of feedback loops in different frequency areas). With power
to all audio components turned off, connect the S curve 215 to the monitor mixer, preferably
at its main mix inserts (if these are not available, connect the unit in-line, between the moni-
tor mixer outputs and the monitor amplifier inputs). (See pages 8-9 in this manual for typical
configuration diagrams.)
Next, power up all audio equipment (turning on the amplifiers last) and, using one monitor
output only, gradually turn up the volume while a performer is speaking or singing into the
primary mic for that monitor. Continue slowly increasing the volume until a feedback howl
just begins. Using your ears or an RTA (Real Time Analyzer), identify the approximate fre-
quency at which this feedback occurs. Lower the corresponding Equalizer slider until the
feedback disappears. Then continue slowly turning up the volume until another feedback
howl just begins. Again identify the approximate frequency of this feedback and lower the
corresponding Equalizer slider until the feedback disappears. Repeat this procedure until
you reach the point where many different frequencies begin to feedback at once or when you
find that you’ve already attenuated most of the feedback frequencies that are occurring. This
is the point at which the process stops—you’ve gotten as much gain out of the monitor sys-
tem as you can without adjusting the physical placement of the mic or monitor speaker.
Repeat this procedure for each monitor output (each time using the primary mic for that mon-
itor).
When done successfully, “ringing out” (which should be done before every performance) can
add another 3 to 15 dB more of usable gain to your monitor system—so it’s well worth the
time and effort!