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5.2. FBX Filter Control
5.2.1. Selecting Filter width
If you’re using the FBX for a music application, the standard 1/10-octave constant “Q” filter is most effective. However, in
spoken word applications, such as lectures or teleconferencing, 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.
5.2.2. Setting number of Fixed vs. Dynamic Filters
To change the number of Fixed filters from the factory default of 9 Fixed and 3 Dynamic per channel, push the NUMBER FIXED
button for 4 seconds. The filters LEDs will flash 4 times and then go out. Release the NUMBER FIXED button, and the LEDs
will begin to light in sequence. When the LED corresponding to the desired number of Fixed filters lights, press the NUMBER
FIXED button again.
IMPORTANT TIP: You can mix 1/10- and 1/5-octave filters in the same channel. If you have an especially bad feedback prob
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lem, try making the first few filters 1/5-octave filters.
5.2.3. resetting FBX Filters
All FBX filters:
To reset all FBX filters, follow the directions in
Section 4.2.
Dynamic FBX filters only:
To reset only Dynamic filters, press RESET DYNAMICS
until the current Dynamic filter LEDs flash and then turn off. Release the button.
5.3. Important operating Considerations
5.31. Power-off 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.
5.3.2. Bypass Mode
The FBX has a true power-off bypass. The signal is unaffected in Bypass mode even if the unit is turned off.
5.3.3. Setup Mode
NOTE: Setup mode is for pre-performance audio setup only, and will cause distortion in your audio program if left on dur
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ing performance.
You must follow the setup procedure outlined in the previous section, and do not play program during Setup
mode. Otherwise the FBX 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 setup mode. Be sure a dynamic filter is set, and if one isn’t, press the
READY button before your program begins.)
You’ll know the FBX2410 is in setup mode when the SETUP button is lit.
NOTE: You can manually override Setup mode if necessary.
5.3.4. Mobile vs. Stationary Microphones
One significant advantage offered by the Sabine family of FBX Feedback Exterminator products is their ability to adapt to changing
acoustical relationships involving sound system components in various applications. One major source of potential feedback prob
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lems arises in situations with wireless microphones, when the user of the wireless mic is moving around the performance area. As a
microphone moves in a sound space, with varying degrees of proximity to the speakers and varying acoustic responses, feedback
frequencies may shift. In such a situation, feedback-free mobility may be more important a concern than maximum system gain.
For this reason we recommend setting FBX filters for mobile microphones by moving to the various possible microphone locations
and setting filters for those locations. As the Setup instructions show, raise the system gain and set the FBX filters in each predict
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able location.
In some situations, increasing the number of dynamic filters (versus fixed FBX filters) may allow a second layer of defense against
new feedback from new locations. This technique is recommended if you cannot predict where the performer may roam. But fixed
FBX filters placed in the setup procedure are still your best bet because the feedback filters are already set.
SeCtIon FIVe — How to USe FBX FeAtUreS
5.1. Gain
There is no gain control on the the FBX2410. For best results adjust the mixer or channel output that is patched into the FBX
so at least two of the LEDs on the FBX2410's input meters are lighting up steadily. Do not exceed the clipping level, indicated
by the red LED in the input meter. The FBX is a unity gain device, so the output level of the unit will be virtually identical to
the input level.
Dynamic FBX filters: Factory default of 3 Dynamic
filters flashing just before reset.
5.3.5. Balanced/Unbalanced Mode Settings
If the FBX outputs are connected to an unbalanced connector, as they would be in most insert applications, there will be a 6
dB loss through the box. In this case, if the user wants to have unity gain through the box, the FBX can be put into unbalanced
mode. This will give the box a 6 dB boost at the outputs, making up the loss due to unbalanced connections. Note that in this
mode, if the outputs are connected to a balanced connector, then there will be a 6 dB gain through the box.
