Toa TS-780 Series - Manual (Page 12)

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5.4. FBS (Feedback Suppressor) Function
An annoying screeching sound may be produced when using a public address system. It is referred to as
"Acoustic feedback*" that will occur at various frequencies depending on the surrounding environment.
The unit's built-in Feedback suppressor (FBS) function effectively suppresses acoustic feedback through
simple operation (depresses the volume level at the feedback frequency). If the built-in FBS function cannot
deal with the acoustic feedback, an external graphic equalizer (prepare separately) can be used for more
effective feedback suppression.
* It will occur when a feedback loop is formed in the process that sound from a speaker is picked up by a
microphone, re-amplified, and output through the speaker.
5.4.1. Using the built-in FBS function
Normally set the FBS function to the automatic operation mode (AUTO mode).
Note
If acoustic feedback cannot be suppressed with the built-in FBS function, widen the distance between the
Chairman unit and Delegate units, reduce the output volume, or use an external graphic equalizer. (See p. 13
"Using an external graphic equalizer.")
5.4.1.1. Using in automatic operation mode (AUTO mode)
Set the Feedback suppressor switch to the AUTO position.
The FBS function automatically searches frequency that will cause acoustic
feedback and suppresses the feedback by decreasing the volume level at
such frequency.
5.4.1.2. Using in manual operation mode (MANUAL mode)
If acoustic feedback does not stop even using the FBS function in automatic operation mode, follow the
procedure below to search the frequency that caused feedback, then suppress the feedback.
Step 1. Set the Feedback suppressor switch to the MANUAL position.
Step 2. While gradually rotating the Feedback suppressor control knob
counterclockwise until it stops, seek the feedback point.
If acoustic feedback point is found, stop rotating the knob and do not
touch it any more.
Note
Do not apply excessive force to the knob when it comes to a stop, as
doing so may cause damage to the knob.
Step 3. If acoustic feedback does not stop even when the knob reaches the
immovable position, seek the feedback point by gradually rotating the
Feedback suppressor manual control knob clockwise to its stop.
If acoustic feedback point is found, stop rotating the Knob and do not
touch it any more.
Note
When feedback occurs again, repeat Steps 2 and 3 to find the
feedback point once again.
OFF AUTO
EXT MANUAL
OFF AUTO
EXT MANUAL
Rotate counterclockwise.
Rotate clockwise.