8
Using the LOCK FIXED feature
In very few situations the FBX may mistake music for feedback
and drive the fixed filters deeper than necessary, such as in a
church with a pipe organ, or during a performance with a great
deal of intentional sustained electric guitar feedback. You can
prevent the fixed filters from deepening beyond their preset
depth by pressing the LOCK FIXED button on the front panel
after setup. The LOCK FIXED LED will light to indicate that the
FBX is in LOCK FIXED mode. The fixed filters stay locked until
you press the LOCK FIXED button again.
Selecting filter width
If you're using the FBX for a music application, the standard 1/
10-octave Constant Q filter is usually preferable. However, in
spoken word applications, such as lectures or teleconferenc-
ing, we recommend using the wider 1/5-octave filter for more
robust feedback control. You may enable the 1/5-octave filters
by pressing the "FIFTH OCTAVE" button, and the built-in LED
will light. Only filters set after pressing the button in will be 1/
5-octave. Press the button again to set subsequent filters to
standard 1/10-octave filters. You can mix filter widths in the
same channel (see "IMPORTANT TIP" below).
Important Operating Considerations
Memory
The FBX stores the positions and depths of the filters in
nonvolatile internal memory when the unit is turned off or
during a power failure. The unit will return all filters to their
previous frequencies and depths when it is turned back on.
Bypass Mode
The FBX has a true power-off bypass. The signal is unaffected
in BYPASS MODE even if the unit is turned off. Please note
that if a combination of BALANCED and UNBALANCED
inputs and outputs is used, the signal may be discon-
nected in BYPASS MODE.
Resetting the filters
The user must reset the FBX if the microphones or speakers
are moved significantly. To reset the unit, place the PA system’s
master volume to minimum and then press the RESET button
until the LEDs flash about 4 seconds — and the FILTER LEDs
stop flashing. Then follow the system initialization procedure
explained previously.
TURBO Mode Setup
The FBX-1020 incorporates TURBO mode setup, which is
indicated by a flashing red “CLIP” LED. This lightning-quick
setup feature cuts the time for FBX filter initialization to just a
few seconds, and it reduces the volume level of the feedback
during setup. The 1020 is set in TURBO mode at the
factory and automatically engages every time you
press RESET (resetting filters). The 1020 automati-
cally returns to normal program mode when the first
dynamic filter is set or when you press the front panel
LOCK FIXED button. ALL FILTER LEDS WILL CYCLE TO
INDICATE THE FBX IS ABOUT TO EXIT TURBO MODE.
WARNING: TURBO Mode will cause distortion in your
audio program — it is for setup only. You must follow the
setup procedure outlined in the previous section, and do not
play program during TURBO setup mode. Otherwise the 1020
will clip, and filters may be set improperly. (Clip level is set to
the lowest level so the feedback clips quickly; therefore, your
program will also be clipped in TURBO mode. Be sure a
dynamic filter is set, and if one isn’t, press the LOCK FIXED
button before your program begins.) You’ll know the 1020
is in TURBO mode if the red CLIP LED flashes when no
other signal level LEDs are lit.
Defeating Turbo Mode
You can manually override TURBO mode if necessary: Press
LOCK FIXED (the LOCK FIXED light will turn on), then press
it again. (LOCK FIXED light will go out).
Mobile vs. Stationary Microphones
One significant advantage offered by the Sabine family of FBX
feedback eliminator products is their ability to adapt to chang-
ing acoustical relationships involving sound system compo-
nents and various user applications. One major source of
potential feedback problems arises in situations with wire-
less microphones, when the user of the wireless mic is
moving around the stage/auditorium. As a microphone moves
in a sound space, with varying degrees of proximity to the
speakers and varying acoustic responses, feedback frequen-
cies may shift. In such a situation, feedback-free mobility may
be more important a concern than maximum system gain.
One method of setting FBX filters with mobile microphones is
to turn a microphone on and walk around to the various
possible microphone locations. At the same time, raise the
system gain and set the FBX filters one at a time.
In some situations, raising the number of dynamic filters
(versus fixed FBX filters) may allow a second layer of defense
against new feedback from new locations. However, in many
mobile microphone set ups, fixed FBX filters will protect
against feedback across the range of microphone mobility.
