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An electric guitar pickup is an inductive sensor. In its simplest form, it consists of a coil wound around one or more permanent magnet pole shoes. This is the architecture of some of the most important and popular pickup designs, including regular Stratocaster pickups. The inductive sensor is located under a string made of magnetic metal. When the string vibrates, a signal is generated in the coil. This signal is amplified to produce the sound of an electric guitar.
This is an inherent technical discussion.
The most common way you see a representative string interacting with a pickup is from the angle of the pickup's magnetic field. In this interpretation, the magnetic field of the pickup is "disturbed" by the vibration of the strings. The metal string will pull the magnetic field of the pickup when the pickup vibrates, so that the coil generates a signal according to the change of the magnetic field.
How exactly is the signal generated?
This is a perspective view of the pickup features that you usually see in books, websites and forum posts written by pickups, guitarists and gear heads. Go ahead and search, "How does an electric guitar pickup work?", This is pretty much everything you will get in one form or another. Given the universality of this view, it is easy to understand why the role of the magnetic field geometry of the pickup itself has been taken very seriously in the discussion of pickup design, tone, and performance.
But there is another perspective, which is more common in physicists and engineers' books on pickup. This is also proposed by the National High Magnetic Field Laboratory. This explanation focuses on the string itself as a magnet. The magnetic field of the pickup magnetizes the string in the area above the pole piece. When the string vibrates, it becomes a source of magnetic flux, essentially a magnet that moves near the coil. In this model, the coil is simply a receiver that receives the magnetic flux generated by the moving magnetized part of the string.
These are two fundamentally different signal generation mechanisms. First, the important part of the equation is the magnetic field of the pickup, and the movement of the magnetic field lines of the pickup itself will generate a signal. The second mechanism is that the string itself is a vibrating magnet. As long as the string is magnetized, it does not actually need the pickup to have its own magnetic field.
But which is correct? Let's do an experiment to find out. We make a Zexcoil pickup, everything is complete except the magnet. It still has coils, ferromagnetic pole shoes and structural elements, but no magnets and no magnetic field. We picked up this pickup without a magnet and hung it above the guitar so that it was at the same distance from the strings as the magnetized pickup installed in the guitar. Then we switch between them.
What do you think will happen?
If the center model of the pickup is correct, a magnetless pickup should produce a much weaker signal than a magnetized pickup installed in a guitar because it is located in a region with a lower magnetic field strength, as shown in Figure 4. The magnetic field generated by the magnetized pickup rapidly decays with distance, and since there is no magnetic pickup without its own magnetic field, it can only acquire signals from the wave field lines of the relatively far-away magnetized pickup.
If the string center model is correct, the strength of the signals from the two pickups will be equal, as shown in Figure 5, because they are both equidistant from the vibrating magnetized string (the source of the magnetic flux).
Most of your understanding of how pickups work is wrong, or at least incomplete. A pickup without a magnet sounds exactly like a pickup with a magnet. The pickup does not need a magnet at all, only a magnetized string! Now, of course, in fact, the easiest way to magnetize the strings is to integrate the magnet into the pickup, so that's why we do it.
Ironically, Seth Lover, the inventor of PAF, believes that these physics are absolutely correct. Seth Lover said in an interview with Seymour Duncan in 1978:
“…...the magnetic field comes up to the stings there and magnetizes the strings. That’s one of the things that most people don’t understand. They figure that string is waving there and cutting the magnetic lines of force. Nuts. That isn’t it. The magnet, all it does is magnetize the string. Now you’ve got a waving magnetic field. And we have a fixed coil with a waving magnetic field to induce voltage. If you want to, take the magnet out. One you’ve magnetized your strings, it will play until the string loses it. Players think the string, the magnetic field from the magnet comes up to the string and by twisting the magnetic flux back and forth that’s what induces the voltage. That's not what happens."
Therefore, we can see that the role of the pole shoe as a magnet and the role of the magnetic field generated by the pickup is greatly exaggerated. Our simple experiments show that the most important function of pole shoes as magnets is to magnetize the strings, and the most important magnetic field is the field related to the vibrating strings, not the static field related to the pickup itself. . In a sense, and for analytical purposes, as long as the strings are magnetized, we can effectively ignore that the pickup contains a complete magnet. Therefore, the most important role of the pole shoe in setting the tone is not as a generator of the magnetic field, but as a receiver of the magnetic flux radiated from the vibrating string. The importance of pole shoes as concentrators and filters for magnetic flux becomes more apparent in a chord-centric view. That's what I realized a few years ago, and that's what we manipulate in our pickup design to adjust the pitch. We design pole boots, using some familiar materials and novel and exotic metals that many others never thought of, to enter the pitch exactly where we want it.