About Acoustic Feedback - Fishman LOUDBOX PRO Owner's Manual

About Acoustic Feedback

Feedback usually occurs in the lowest octave of your instrument, generally with two notes about a half step apart.
Like blowing air across a bottle, the lower type of feedback (cavity resonance) starts when the sound pressure coming
out of the speakers excites the resonant air chamber inside your instrument. We have found that it is effective to tune
out an instrument's cavity resonance feedback with the Anti-Feedback (notch filter) in the Loudbox. 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 find the position that subdues top resonance feedback.
Front Panel -
Channel 2
XLR Phantom
Power Clip
48V
Channel 2
XLR Phantom
Clip
Power
48V
Phantom Power FAQs
What devices are safe with 48V phantom power?
1 Phantom-powered condenser microphones
2 Balanced dynamic microphones
3 Many new wireless units
4 A preamp/DI designed for phantom-power operation, such as the Fishman Pro-EQ Platinum
What devices are potentially unsafe with 48V phantom power?
1 An unbalanced dynamic mic
2 A balanced line-level device that is not designed to accept phantom power (ex: some effects processors)
3 A balanced wireless receiver that is not designed to accept phantom power. Consult the manufacturer of the
wireless unit for compatibility
4 An unbalanced signal from an instrument preamp or stompbox
Important Note: Turn off phantom-power if you plug any of the above into the XLR input.
Channel 2
XLR Phantom
Power Clip
48V
Channel 2
XLR Phantom
Power Clip
48V
Channel 2
(microphone or instrument channel)
XLR Input
Gain Low
Plug in any balanced dynamic or condenser microphone here. You may also connect
an outboard preamp with balanced XLR out to this input. Note that the XLR input will
shut off if you attempt to use it simultaneously with the Channel 2 (¼") input.
Phantom Power Switch
Gain Low
Provides 48 Volts phantom power to the XLR Input for condenser microphones and
phantom-powered preamp/DIs.
Gain Low
¼" Input
This input has a very wide operating range. It will accept high- or low-level signals
from active or passive pickups. Note that the XLR input will shut off if you attempt to
use it simultaneously with the Channel 2 (¼") input.
Gain Low
Clip LED
The Clip LED will flash when the gain level is too high and the signal becomes
distorted. If the light comes on when you play, lower the gain until the distortion goes
away. Note that the clip LED monitors both the Channel 2 XLR and ¼" inputs.
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