Zexcoil's Scott Lawing serves up the 411 on pickup design.
In part I, we discussed the construction and basic function of a pickup, along with the implications of the resistance of the coil. In part
Zexcoil's Scott Lawing serves up the 411 on pickup design.
In part I, we discussed the construction and basic function of a pickup, along with the implications of the resistance of the coil. In part II, we will discuss pickup inductance in detail, focusing on the electromagnetic properties of the materials that make up the pickup and how they affect pickup performance.
As we discussed last time, we’re going to be looking at all of these physics in terms of how the pickup interacts with the flux generated by the vibrating, magnetized string. We’re basically assuming that the string is magnetized, independent of the pickup. We’ll be talking a lot about magnets and magnet materials, but we’re not really concerned with pickup magnets as magnets at all, we only care about how they behave as conduits for the magnetic flux emanating from the string, at least for most of the analysis.
That’s a good segue, and before we get into inductance proper, let’s talk about pickup construction materials in terms of their role as conduits for magnetic flux. To do that, we have to define something called magnetic permeability. Magnetic permeability can be defined as the ease with which a material can support the development of a magnetic field within itself. The symbol for magnetic permeability is µ (pronounced “/mju/”). Magnetic permeability is analogous to electrical conductivity (conductivity being the inverse of electrical resistance, which we talked about last time), so magnetically permeable materials act as conductors of magnetism. Air is neither a conductor nor a resistor of magnetic flux, it’s basically magnetically transparent, with a relative magnetic permeability, µ, equal to 1. The low carbon steel typically used as humbucker pole pieces may have a relative permeability in the thousands, meaning it is thousands of times more magnetically conductive