We've just bought a Xenyx 1222 mixer.
When setting the gain, we're not getting much past 40% on the mic channel before we start getting feedback . The mixer has Feedback detection on it but none of the equalizers are indicating any feedback .
We do use the Hall FX on the mic channel but the feedback occurs without speaking into the mic. But this did also occur when the FX were off
I've seen a youtube review that states using the compressor can can cause feedback . Does it?
Any suggestions on what the cause could be and how to eliminate it are welcome
Feedback on Behringer Xenyx mixer
Re: Feedback on Behringer Xenyx mixer
Feedback happens when the system loop gain exceeds unity.
In other words... the mic picks up the sound from the PA speaker(s), either directly or after being reflected around the room. The signal reaching the mic is amplified by the preamp, and through the mixer, and then by the PA amplifier or active speaker before being emitted by the speaker and getting back to the mic.
That's the loop.
If the sum of the gains in that loop add up to more than 0dB overall, the system will howl-round. (The preamp and power amp add the gain, the speaker's inefficiencies and directionality, the mic's sensitivity and polar pattern, and acoustic losses through the air introduce attenuation.)
Because the mic's frequency response isn't flat (and neither is the PA speaker's response), there will be slightly more gain at one specific frequency than others, which is why howl-rounds occur at that set pitch.
A graphic EQ is often used to reduce the gain at the pitch of the howl-round, which will kill it, but if you then increase the overall system gain further it will howl-round at a new, different frequency where the overall gain is more than 0dB again.
Skillful setting of a graphic can usually achieve 6dB or more extra gain in the system than without, but it's very easy to degrade the sound quality of the system with too much 'feedback correction'.
The way to prevent (or reduce) feedback is self-evidently to reduce the amount of sound reaching the mic from the PA speakers (and/or the floor monitors).
You can achieve that by making sure the PA speakers are well forward of the microphones, and/or use PA speakers with well controlled sound dispersion to minimise the amount of sound getting back to the mics.
Also, aim the null(s) in the microphone polar pattern to reject as much sound as possible from the floor monitors/PA speakers, and avoid using omni-directional mics!
Compressors don't cause feedback per se, but poor use of compressors can.
Most compressors have a 'make-up gain' facility, which is intended to maintain peak levels while raising quieter elements. However, that make-up gain adds to the preamp's gain when the compressor isn't introducing gain reduction, and that's what causes howl-rounds. Simplistic 'one-knob compressors' usually have automatic make-up gain...
Compressors can be useful tools for reducing uncontrolled peaks, but only if configured so as to make loud stuff quieter, not to make quiet stuff louder!
In other words... the mic picks up the sound from the PA speaker(s), either directly or after being reflected around the room. The signal reaching the mic is amplified by the preamp, and through the mixer, and then by the PA amplifier or active speaker before being emitted by the speaker and getting back to the mic.
That's the loop.
If the sum of the gains in that loop add up to more than 0dB overall, the system will howl-round. (The preamp and power amp add the gain, the speaker's inefficiencies and directionality, the mic's sensitivity and polar pattern, and acoustic losses through the air introduce attenuation.)
Because the mic's frequency response isn't flat (and neither is the PA speaker's response), there will be slightly more gain at one specific frequency than others, which is why howl-rounds occur at that set pitch.
A graphic EQ is often used to reduce the gain at the pitch of the howl-round, which will kill it, but if you then increase the overall system gain further it will howl-round at a new, different frequency where the overall gain is more than 0dB again.
Skillful setting of a graphic can usually achieve 6dB or more extra gain in the system than without, but it's very easy to degrade the sound quality of the system with too much 'feedback correction'.
The way to prevent (or reduce) feedback is self-evidently to reduce the amount of sound reaching the mic from the PA speakers (and/or the floor monitors).
You can achieve that by making sure the PA speakers are well forward of the microphones, and/or use PA speakers with well controlled sound dispersion to minimise the amount of sound getting back to the mics.
Also, aim the null(s) in the microphone polar pattern to reject as much sound as possible from the floor monitors/PA speakers, and avoid using omni-directional mics!
Compressors don't cause feedback per se, but poor use of compressors can.
Most compressors have a 'make-up gain' facility, which is intended to maintain peak levels while raising quieter elements. However, that make-up gain adds to the preamp's gain when the compressor isn't introducing gain reduction, and that's what causes howl-rounds. Simplistic 'one-knob compressors' usually have automatic make-up gain...
Compressors can be useful tools for reducing uncontrolled peaks, but only if configured so as to make loud stuff quieter, not to make quiet stuff louder!
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- Hugh Robjohns
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Posts: 43691 Joined: Fri Jul 25, 2003 12:00 am
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Technical Editor, Sound On Sound...
(But generally posting my own personal views and not necessarily those of SOS, the company or the magazine!)
In my world, things get less strange when I read the manual...
(But generally posting my own personal views and not necessarily those of SOS, the company or the magazine!)
In my world, things get less strange when I read the manual...