Each of the pickups on a Strat is a single coil of wire wound on a plastic bobbin with six small magnets. The magnets are all positioned with the same pole at the top. This is the most basic type of pickup, and has been in existance since sometime in the 1930's.
Any time you get a wire moving in a magnetic field, or in this case, a magnetic field moving near a wire, there is a current induced in that wire. Making the magnetic field stronger, or using lotsa
wires (like in a coil), increases this effect.
The pickup magnets create a field; the vibrating strings cause movement in the field; the fluctuating magnetic field induces current in the coil wires; the amplifier boosts that small signal to make it strong enough to drive the speakers. 'Still with me?
Now, adding another pickup makes things interesting. As the string vibrates, it moves in one direction, then comes back in the opposite direction. The current being induced in the coil does the same thing. If both pickups are identical
, the induced current will be flowing in the same direction in both pickups, and they are in-phase
. If any of the characteristics of one
of the pickups is reversed
, the current in that pickup coil will be opposite to the other one, and the pickups are out-of-phase
If these out-of-phase pickups were getting exactly
the same stimulus from the string, the signals they produced would be equal
. They would cancel
each other out, and there would be no signal left for the amplifier to work with.
This doesn't happen on your Strat because the pickups are sensing the vibration at different parts of the strings. The size of the vibration, and the harmonic frequency content at these different locations is just different enough that there is only partial cancellation
. The result is that slightly hollow sound you get with switch positions 2 and 4.
The three pickups in a stock Strat are usually indentical except that the magnets in the middle pickup are 'upside down'. This reverses the magnetic field around the middle pickup, reversing the phase of its signal relative to the other two pickups.
Companies that specialize in such things have developed expertise in 'tweaking' the pickup characteristics to produce different results. 'Hot' pickups usually have more turns of wire on their coils, and/or stronger magnets. Choice of materials gives a lot of options to work with, and everybody has their own personal idea of what the 'ultimate' pickup should be. Humbuckers use out-of-phase cancellation to get rid of the hum induced by the power-line magnetic fields produced by the transformers in big amplifiers. Since this requires having two coils in each pickup, we have the 'lotsa wire' condition which produces a high-output signal 'chunky' sound.
There are thick books available which are devoted to this subject. I'm going to knock off now, rather than write another one here. Hit the library. Do some reading. You'll be amazed at how much is going on inside the gizmos we take for granted.
I haven't looked at it lately, but this website can generally give you a start on understanding just about anything: http://landau1.phys.virginia.edu/Education/Teaching/HowThingsWork/home.html
Keep asking about things. There aren't any stupid questions, although sometimes you can
get stupid answers.
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