4
4.1. Before You Begin
These instructions apply to both the FBX1200 and the FBX2400. The 2400 is a dual-
mono version of the 1200. Your FBX Feedback Exterminator will improve any sound
reinforcement system. The instructions presume that you are familiar with the funda-
mentals of sound reinforcement.
4.1.1. Where the FBX fits in your sound system:
The most common patch point is between the output of the mixer and the input of
a power amp. In this position, the FBX can sense and eliminate feedback occur-
ring in any channel of the mixer. An even better solution is on a mixer insert point
for a single channel, or a subgroup (see application diagrams in
Section Two —
Applications
). This targets the feedback control to the mics that need it.
Note:
If you’re using a mixer with unbalanced 1/4" outputs, you must use standard
unbalanced cables and connectors when connecting it to the FBX. Similarly, if
your mixer is wired for balanced 1/4" Tip-Ring-Sleeve (TRS) outputs, you must use
that type of connector. If you don’t, you may experience a loss of gain (up to 6 dB)
when using the FBX. This can occur if either side of the balanced output is grounded
at any point (or when mixing balanced and unbalanced inputs and outputs).
4.1.2. A note about graphic equalizers:
The
FBX is designed to replace the graphic equalizer’s function for eliminating
feedback. In many applications, such as churches, auditoriums or small acoustic
ensembles, the mixing board provides all the tonal control that is necessary. The
FBX can replace the graphic EQ altogether in some applications; however, a graphic
equalizer may be beneficial to shape a system's total performance. If you do want
to use an equalizer, place the FBX after the EQ in the signal path. Use the EQ’s
controls to shape the tonal response of the sound system, but DO NOT NOTCH
FOR FEEDBACK.
4.1.3. Understanding FIXED and DYNAMIC filters
Before operating the FBX, you need to understand the two types of FBX filters:
FIXED and DYNAMIC. FIXED FILTERS retain their frequency center-points until
the unit is reset by the user. The system’s gain before feedback is limited primarily
by the number of fixed filters; i.e., increasing the number of fixed filters increases
the system’s gain before feedback. In addition, you can LOCK the fixed filters so
they do not get any deeper. Locked fixed filters are no longer adaptive. The
FBX's
DYNAMIC FILTERS control intermittent feedback that comes and goes through-
out the program. They are continually reset automatically to different frequencies
as new feedback occurs during the program.
For most applications, the optimal
setting is nine FIXED and three DYNAMIC FILTERS. This is the factory de-
fault.
4.1.4. Setup & Ready
Your FBX Feedback Exterminator is either in Setup mode or in Ready mode.
Setup Mode:
It’s quick and quiet, but use this mode for setup only – do not use
the FBX for your program while in Setup mode. Think of Setup mode as your key
to achieving one of the main benefits of the FBX: getting more gain before feed-
back. In Setup mode you will be raising the gain of your system so the FBX can
place transparent filters (Fixed Filters) that will allow you to get all the gain you
need for a loud and clear show. In Setup the FBX is very sensitive so
do not talk
into the mics during setup
, and try to keep room noise to a minimum. If the room
is noisy, then go into Ready mode and raise your gain while the fixed filters are still
unlocked (flashing Ready LED).
Ready Mode:
Let the show begin. Your fixed filters are eliminating feedback and
giving you extra gain, and your dynamic filters are ready to jump on any new feed-
back during the show. In this mode your fixed filters are either locked (red LEDs)
or unlocked (amber LEDs). We recommend locking your fixed filters for the show.
But if you don’t have time for the Setup mode, or if the room is just too noisy during
setup, then you can start off by unlocking the fixed filters. Leaving the fixed filters
unlocked allows them to get deeper if needed, which can be handy if you need to
get more gain before feedback. But once your system stabilizes we recommend
you lock the fixed filters for the duration of the show!
SECTION FOUR — OPERATING INSTRUCTIONS