The electric guitar is probably one of the most indispensable instruments in modern music. Today, I would like to talk about the pickup, which is the most critical part of an electric guitar. But before we go any deeper into the pickup, we had better understand how the vibration of the string, which is some sort of mechanical vibration, can be transformed into electric signals in the first place.
We owe this to the Faraday’s law of induction,
which basically says that the change in magnetic flux ΦB, in a coil causes electromotive force (e.m.f., ε), which is the difference in voltage between the two ends of the coil.
What is the magnetic flux then?
You may see the formal definition above. But we are not assuming that we are math or physics experts, so forget the horrifying double integral stuff. For better understanding, we can take the number of magnetic lines of induction that goes through this closed surface formed by the coil as the magnetic flux.
In short, Faraday’s story says that with the change in the number of lines crossing the coil, we do get some sort of electric output, which is the voltage difference.
But what does this have to do with the pickup?
Actually, it is a similar model. A pickup consists of a permanent magnet and a coil around it. Above the magnet is the cross section of a string. The metal string is magnetised so that some of the string’s magnetic lines of induction run through the coil. The vibration of the string causes an alternating change of magnetic flux in the coil will result in alternating e.m.f. Now if we close the circuit, you get alternating current. This is the electric signal we want.
If you are familiar with math, the string vibration is something like a trigonometric function. You differentiate it you get another trigonometric function, then you can argue that the vibration is in this way transformed into an electric signal.
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