About Acoustic Feedback - Fishman Loudbox Performer User Manual

About Acoustic Feedback

Feedback usually occurs in the lowest
octave of your instrument, generally with
two notes about a half step apart. The
lower type of feedback (cavity reso-
nance) starts when the sound pressure
coming out of the speakers excites the
resonant air chamber inside your instru-
ment. We have found that it is effective
to tune out an instrument's cavity reso-
nance feedback with the Anti Feedback
(notch fi lter) in the Loudbox Performer.
For acoustic guitar this occurs at G# on
the low E-string, or at about 100Hz. Turn
the Anti Feedback knob to about 11
o'clock to dial out this resonance.
Note that the circuit can be effectively
defeated by moving the dial to the Off
(7 o'clock) position.
The higher range of feedback (top
resonance) usually starts about a half or
whole step above cavity resonance of
the instrument. Top resonance feedback
happens when the sound pressure
coming off the speakers excites the
resonant frequency of the soundboard
of your instrument. For acoustic guitar
this occurs at A and above on the low
E-string. Push the Phase switch in and
out until you fi nd the position that
subdues top resonance feedback.
Feedback
Lower
Feedback Range
(E to G#)
OFF
Upper
Feedback Range
(A and above)
14
Anti
Phase