Acoustic Guitars and the "Goose" Effect
You get on stage, plug in your acoustic guitar, tweak the sound and start playing. Things are rolling along fine, and then, suddenly, in the middle of the song, an obnoxious "honk" slaps you (and the audience) in the face!
You turn a few degrees to the right and the honking stops. Then back to the left and the howling returns. A few degrees further to the left and it stops. Then you move slightly again and it roars back with a vengeance.
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