humbucker
The humbucker's main coil has adjustable pole-pieces which can be screwed up or down. Those in the secondary coil are fixed. Both sets of pole-pieces come into contact with the same magnet, situated below and between them on the base plate. The polarity of the secondary coil is opposite yo that of the main coil because the two sets of pole-pieces are in contact with the opposite poles of the bar magnet.
A humbucker is a type of pickup consisting of two electromagnetic coils of opposite polarity. It is specially designed to reduce interference from other electronics that can cause a hum. The humbucking, or twin-coil, pickup was invented by Gibson engineer Seth Lover in 1955.
The two coils of the humbucker are wired in series, so that the current flows first through one then the next, but out of phase with each other. This means that any rogue interference is sent by one coil as a positive signal and by the other as a negative signal. The two opposite currents, flowing in different directions, therefore cancel each other out, and the hum is not passed on to the amplifier.
To ensure that the two coils do not cancel out the currents generated by the vibrating strings as well. the sets of pole-pieces within each coil have opposite magnetic properties. The result is that when the secondary coil inverts the signal from the disturbed magnetic field it duplicates – instead of cancelling – the electrical pulse. When the two signals are the same, they are said to be in phase.
