ELI5 : Why do guitar amplifiers give off bad feedback? guitars in giant rock concerts don’t normally do this, how they can be so loud without feedback?
In: Technology
Feedback is caused by an amplified signal finding a sympathetic resonance with the guitar producing that signal, getting louder and louder until it no longer resembles the original tone. It happens most commonly when the amp is absurdly loud for 2 reasons: 1) a cranked amp applies a LOT of gain to the signal. 2) A loud amp is more likely to vibrate the strings or internal components of the guitar’s pickups.
That said, in most concerts it’s not actually that loud on the stage. Even playing small clubs as a rock band you’ll more often see amplifiers mic’d up and put through the house PA and not cranked to fill the room. The PA speakers being in front of the stage and pointed away from the band so the majority of their sound goes towards the audience can can’t cause feedback. Stage volume is actually downright reasonable in most cases unless the sound system isn’t operated correctly or undersized. And even then, if you turn your back to the amplifier a lot less sound gets to your guitar because your body is in the way, which is why when you do see guitarists try to create feedback on purpose, they’ll turn around and face their guitar towards the amp.
And if you think it’s disappointing to go on stage with a half stack and not really turn it too far past like…3. In your stereotypical “giant rock concert”, most of those amps [are fake](http://www.metalsucks.net/wp-content/uploads/2013/07/Immortal-fake-cabs-604×453.jpg).
You might have one cabinet mic’d up or in more modern cases…they’ll use a direct output from the their amplifier “head” and run it directly through the house PA with no actual guitar amp on stage. Think…plugging your phone into the car’s AUX input or using bluetooth connection to the onboard stereo system.
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