Dead Magnet

Discussion in 'Just Pickups' started by 61fury, Mar 23, 2016.

  1. Antigua Tele

    Antigua Tele Friend of Leo's

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    One possible benefit to the electromagnetic would be to control the amount of Gauss, but you could also do that by mechanically moving a bar magnet away from the pole pieces. DiMarzio's "Airbucker" simply puts space between the pole piece and magnet. Imagine what might happen if a little lever on the side of the pickup allowed you to move a strip of permeable material into the "air space".
     
  2. Deneb

    Deneb Tele-Afflicted Ad Free Member

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    This is the good idea. If you are in the truest sense talking about a lever (on the mechanical switch) for moving a magnet in a pickup.
     
  3. jefrs

    jefrs Doctor of Teleocity

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    I just happen to be a professional physicist and that's the biggest load of tosh I've heard for a long while.
     
  4. Antigua Tele

    Antigua Tele Friend of Leo's

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    Please, do go into detail. It's been the "professionals" who have been the some of the biggest let downs when it comes to clarifying the function of guitar pickups. Start from the top, work your way through, call out every error you can find and explain why you believe the statements to be incorrect.

    Also, since you have invoked your credentials, would you please state your education, specific area of expertise, and/or your profession?
     
    Last edited: Apr 19, 2016
  5. jefrs

    jefrs Doctor of Teleocity

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    Easy demo - sprinkle some iron filings on your pickup and watch the filing 'dance' as the vibrating string interferes with the magnetic field (yes it really does). There's nothing else moving besides the string so it must be the string altering the magnetic field and the string lacks sufficient mass to have a significant field of its own.
    Tip - put some cling film over the pickguard and pickups so the filings can be removed.
    Nota if you have iron filings stuck to a pickup you get a rather nasty 'gritty' sound, and they can be on the underside, iron filings or frits (iron ore gets into brick clay) from brick dust are bad news, use Bluetak to remove them.

    Physicist-engineer, PhD level specialising in radiometrology, which means measuring radiation, any form of radiation.

    Why do I think it is wrong - a colleague came up with a very apt term for nonsense pseudo-science advertising blurb "added BS".
     
  6. Antigua Tele

    Antigua Tele Friend of Leo's

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    This is demonstrably false, and it's the underlying basis of your misconception: a piece of permeable material cannot be both too weak to have a significant field of it's own, and yet be strong enough to magnetically effect something else. If you have one condition, then the other is true by necessity.

    Here's a very real demonstration that the strings have their own magnetic fields. This is called "magnetic film". Where you see dark green, lines of flux a perpendicular to the film. Where you see light green, the flux lines are parallel to it:

    [​IMG]

    As you can see, the strings are magnetized, and their cross section would have lines of flux that look like this:[​IMG]

    It's the two round regions where the flux is oriented horizontally that creates the light green lines that coincide with each string, and is strongest directly over the pole pieces.


    As for the notion that the strings are "altering the magnetic field", familiarize yourself with adding magnetic fields:

    http://www.emfs.info/what/adding/

    So what you have is a pickup with a magnet, it's not moving, so it's flux change is zero. Then you have a moving string, it causes flux change in the coil that is not 0, let's call it "non-zero string flux movement". In other words:

    zero pickup flux movement + non-zero string flux movement = non-zero string flux movement

    Since the pickups's permanent magnet flux is not moving, it is zero, can be thought of as though it's not even there, and the only changing flux vector you are left with is the flux of the moving string and it's magnetic field, as seen in the magnetic film above. I see no reason why the string's magnetic fields would not also move magnetic filings, if they were present.
     
    Last edited: Apr 20, 2016
    teleaddicted likes this.
  7. jefrs

    jefrs Doctor of Teleocity

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    You are not demonstrating anything that disproves what I said and you are trying to make it complicated for the sake of making it complicated.
    The translucent film is simply showing where the strings focus or distort the pickup magnets' field. Whilst it is possible to permanently magnetise a region steel string, its magnetic force will be very weak due to its small diameter hence mass, plus many strings are stainless steel which will not permanently magnetise (not ferromagnetic). The strings do distort the pickups' magnetic field and vibration causes a change in that ferromagnetic field which is what generates a small current in the pickup coil. It is generally felt that it is the strings' inward and outward movement, not side to side, that causes the induction of current. This is all well established stuff, some of it well over a century old: Henry, Tesla, Faraday, Maxwell, Siemens
    If you place a few iron filings on the pickup poles, you can see them dancing as the stings vibrate.
    The strings themselves are too small to provide a sufficient field to do that but they can shift the pickup's field.
    Practically anything passing through a magnetic field will distort it, all materials have greater or lesser magnetic properties, some are even repelled.
     
  8. Antigua Tele

    Antigua Tele Friend of Leo's

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    Your entire premise is wrong. Magnetic fields do not actually "distort" in any real sense. Here is the reason:

    Magnetic fields adhere to the principle of superposition https://www.pa.msu.edu/courses/2000fall/phy232/lectures/interference/superposition.html What this means is that when you put two magnets close together, they do not actually change eachother's magnetic fields, rather then sum together. What you think of as magnetic distortion is just the abstraction of having added the two magnetic fields together.

    Knowing that magnets relate to one another is a purely additive way, it's logically obvious that the guitar string adds and subtracts it's own acquired magnetism to the sum magnetic field. Since the pole pieces are permeable, they too receive additional sum flux as the string moves closer.

    If the string were a permanent magnet and charged as strongly as it is while being positioned over a magnet in a typical pickup, the pickup would work without any permanent magnet.

    There was an acoustic guitar pickup on the market several decades ago that worked by placing a magnet over the string to give then a permanent charge that would last for some period of time, and then the pickup underneath would work despite having no magnet of it's own: https://books.google.com/books?id=h...Q6AEIITAB#v=onepage&q="String Vision"&f=false
     
  9. teletuner

    teletuner TDPRI Member

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