JBL EON 210P User Manual page 21

Symptom
Noise or hiss heard at outputs
Feedback
Headphone signal is weak
Likely Cause
Noisy source device
Unused channel volumes
are up too high
Microphones are too close
to the speakers
MONITOR OUTPUT
is turned down
Channel Input is too low
Impedance mismatch
What to do
Disconnect the devices that are connected to your mixer one at a
time. If the noise goes away, the problem is with
the source or the connecting cable.
Lower the channel volume on unused channels to "0"
Speakers should be between the audience and the microphones in
order to avoid feedback.
Turn up the "monitor output volume" on the mixer
Make sure that the channel input volume is turned up
Your headphones have too high of an impedance.
Try a different set of headphones.
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