How do they work?

Discussion in 'Pickups & Electronics [BG]' started by iplaybass, Nov 28, 2000.

  1. iplaybass

    iplaybass Guest

    Feb 13, 2000
    Germantown, TN
    Alright, youll probably think im a dufus, but i really have little understanding of how electromagnetic pickups work. I know they pick up sound, i just dont know how. Also, one thing ive been wondering about in particular, how does the wood of the bass affect the sound?
  2. Christopher


    Apr 28, 2000
    New York, NY
    Magnetic pickups take advantage of a phenomenon known as electromagnetic inductance. To wit: variations in a magnetic field generate an alternating electric current (and vice versa). In the case of pickups, the geometry of the field and the current are described by the "right hand rule." If your right thumb points in the direction of the magnetic field, your right hand fingers curl along the direction of the current. The magnetic polepieces in a pickup generate a magnetic field which is disturbed by the vibration of metal strings; according to the right hand rule, the alterations to the magnetic field caused by the moving strings generate an alternating electric current in a plane perpendicular to the magnetic field lines. The wire wrapped around the pickup carries and transmits this current to the output, where it is amplified and turned back into mechanical energy via speakers.

    A magnetic pickup is fundamentally indistinguishable from a dynamic microphone; both use the motion of metal parts in the presence of a magnetic field to generate alternating electric current. The sole difference is that whereas a dynamic mic uses a diaphragm to translate variations in air pressure into current, the "diaphragm" of the magnetic pickup is the string itself. If you're wondering how or why the wood of an electric bass affects its tone, you might as well ask yourself why singers sound different when using mics onstage.
  3. Flatwound

    Flatwound Supporting Member

    Sep 9, 2000
    San Diego
    I'm glad Christopher answered that one. I understood it, but I couldn't have put it as succinctly as he did.

    As far as the wood affecting the tone, the wood also vibrates, and this vibration is picked up by the strings, and so, transmitted to the pickup.
  4. john turner

    john turner You don't want to do that. Trust me. Staff Member Administrator

    Mar 14, 2000
    atlanta ga
  5. notduane


    Nov 24, 2000
    I remember waaaay back in tech school somethin' called a "Linear Variable Differential Transformer" :confused:

    The textbook used a simplistic example :D .
    * Wrap some wire around an air core form (an empty Charmin tube will work just fine).
    * Connect the ends of the wires to a Galvanometer (that thing collectin' dust in your high school Physics lab).
    * Zero (center) the Galv-o-meter.
    * Pass a ferrous, rod-shaped object back-and-forth through the core of the coil ( [​IMG] focus now! ).
    * Watch the G-meter... \|/ \|/ \|/ , etc.
    >> This is the action of a string over a p'up (in a way).

    Examples: A phono cartridge? How about them "rings" `ya see
    in the pavement at traffic lights? A COIL of wire buried
    just under the surface. The ferrous object?...your car!
    Green light! Whoo-hoo! >>>>> [​IMG]