I was reading an article in the newspaper recently that was describing the pickup mechanism on an electric guitar. This is essentially a wire coil wrapped around an iron core that generates a signal from the steel guitar strings vibrating. Since this device operates using electromagnetism, the author tried to make the case that (intentional) feedback while playing was due to getting the guitar near the magnetic field generated by the speakers rather than simple acoustics. Seems unlikely to me, but perhaps a Doper can corroborate.
I’ve always heard that electric guitar feedback was caused by sympathetic vibration of the strings, not electromagnetic interference from the speaker. Here’s a mediocre cite from Howstuffworks that backs up that idea:
It is also possible to get really screechy (screachie?) feed back by being too close to the amp. I suspect this is electromagnetic rather than acoustic, but I’m not sure. It’s caused by the loose coils of the electro magnet inside the pickup vibrating. And it’s really nasty, not cool. Fix it by dipping your pickups in melted parafin (wax) or something similar.
if the guitar in question is either old or cheap, the Neil Young type feedback (dog whistle) is caused by the coils in the pickups vibrating, again because of sound waves hitting it. MOdern pickups are “potted” in epoxy to eliminate this. You can pot old vintage pickups by dipping them in paraffin.
There is another alternative: the e-bow and the sustainer both work by generating a magnetic field that keeps the string or strings vibtrating. It seems to be simple case of applying voltage to the wrong end of a guitar pickup, but maybe I’m oversimplifying that one.
BTW, the core of a pickup is either a ceramic magnet or an alnico (aluminum/nickel/cobalt) magnet. Alnico degausses over time, leading to a change in the sound the pickup makes. Ceramic seems to be more “set.”
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You can pot old vintage pickups by dipping them in paraffin. /QUOTE]
I should have said, you can pot older squeal-prone pickups. Potting vintage pickups on a collectable guitar will probably decrease its value.
The most commonly heard feedback from electric guitars is caused by sound from the speakers causing harmonic string vibrations, which are in turn picked up and sent back through the amp. This is the kind of feedback heard at the beginning of Foxy Lady by Hendrix, for one example. This kind of feedback is even easier to achieve when the guitar in question is a semi-hollow electric, because then the thin wood of the guitar body vibrates as well.
Yes, but harder to control. The solid body was originally made to help eliminate feedback, but with the ability to finely manipulate it, Hendrix and others play(ed) not only the guitar itself, but the feedback loops from the amp as well.
Nifty MLA Cite:
McSwain, Rebecca. “The Social Reconstruction of a Reverse Salient in Electric Guitar Technology: Noise, the Solid Body, and Jimi Hendrix.” Music and Technology in the Twentieth Century. Ed. Hans-Joachim Braun. The Johns Hopkins University Press. 2002. 186-98.
Good info. Thanks. 