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Easy demonstration of how sound in the air comes through guitar pickups

giantslayer

Inspired
I kinda stumbled onto this by accident and it blew my mind.

There has been much discussion on how your guitar actually produces a different tone when you’ve got an amp or monitors producing sound that interacts with the guitar. It’s not just your perception: the sound itself is legitimately different.

I was using the Fender Tune amp (which is free) and using the function (“manual”) where it plays the sound of a guitar string and you can tune to it. I had my little practice amp on and noticed that the sound from my iPhone was getting picked up by my pickups and going through the amp! Super easy, fun experiment for anyone curious.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
That could also be magnetic induction. The speaker in your phone produces a magnetic field. In fact it's more likely that it was magnetic induction rather than acoustic.

For proof of acoustic feedback being a thing you simply rap on the guitar body with something (like your knuckles) and you'll hear it come out of the amp.
 

lauke-lux

Fractal Fanatic
This morning I noticed with a lead patch that when I coughed just above my axe it came through the headphones, some prehistoric sound of deep earth; incredible fun yelling at my axe for a few minutes.

String / speaker interaction is IMHO the thing where axe fx beats all others; at band level it's "better than the real thing" regarding feedback.
 

giantslayer

Inspired
That could also be magnetic induction. The speaker in your phone produces a magnetic field. In fact it's more likely that it was magnetic induction rather than acoustic.

For proof of acoustic feedback being a thing you simply rap on the guitar body with something (like your knuckles) and you'll hear it come out of the amp.
Good point. That’s why lowering pickups gives you a woodier tone: you have less string sound mixed in with the body resonance.

I wonder… is the traditional interaction between amp and guitar magnetic, acoustic, or both?
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Good point. That’s why lowering pickups gives you a woodier tone: you have less string sound mixed in with the body resonance.

I wonder… is the traditional interaction between amp and guitar magnetic, acoustic, or both?
Mostly acoustic but the closer you get to the speaker the more magnetic. If you get too close to a FRFR speaker you can get what is known as "tweeter squeal" as the magnetic field from the tweeter couples into the pickups causing a feedback loop.
 

CodePoet

Power User
Mostly acoustic but the closer you get to the speaker the more magnetic. If you get too close to a FRFR speaker you can get what is known as "tweeter squeal" as the magnetic field from the tweeter couples into the pickups causing a feedback loop.
I got a hard lesson on this at a gig once. It was a tight space and I had my FRFR monitor up off the floor pretty close to me. It squealed like crazy and I had no idea what was happening, so I think I just kept turning it down to near-inaudible levels. That sucked.
 

lauke-lux

Fractal Fanatic
Mostly acoustic but the closer you get to the speaker the more magnetic. If you get too close to a FRFR speaker you can get what is known as "tweeter squeal" as the magnetic field from the tweeter couples into the pickups causing a feedback loop.
To my experience this happened only once at "ear killing" band level, on a floor monitor . At normal level I just experienced "normal" feedback.

BTW would limiting the bandwidth on cab block or power amp diminish this phenomena ? (I guess "no" as the coupling you described does not involve the Axe Fx)
 
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