Re: seymour duncan output specs
Loudness perception has been well understood for over 50 years. It is not in any way ambiguous.
However, my question is about something different altogether.
No it's not. You're just not getting the right combination of information you think you want.
The problem is that what ultimately determines the perceived loudness level of the pickup is a combination of practically every variable that exists in the complete instrument as well as the listener, and many of these variables are interdependent in ways that are difficult to define.
First off, the strength of the magnet used in the pickup matters. A stronger magnet will increase the magnetic flux produced by the string vibrating within the magnet's field, and that produces a higher voltage through the wire coils around it forming the inductor. However, a stronger magnetic field will also "pull" harder on the strings themselves, dampening them and reducing sustain. Ceramic magnets have the potential to be the strongest magnets typically used in guitars, but they can also be the weakest by far, which is why they're seen on boutique builders' highest-output pickups as well as cheap stock coils. Alnico-5 magnets are the strongest "standardized" magnets typically used, followed by Alnico-8, -4 and -2.
Second, the shape and size of the pickup poles matters. The polepieces, in contact with the magnet underneath, "shape" the magnetic field to provide more or less strength in various areas of the pickup. Rail-type pickups have a fairly uniform magnetic field, while separate polepieces create little mini-magnets right under each string. This changes how each string varies the magnetic field with its vibration and thus produces the signal. Rails capture practically everything that happens above them, and so produce a more "accurate" tone based on the actual vibration of the string. Separate polepieces exaggerate the fundamental motion of the string and de-emphasize higher harmonics, and are capable of slightly higher output. In general, the more magnetized metal inside the coil, the stronger the output.
Third, the number of windings around the polepieces, and the volume those windings take up, matters. DC resistance is most directly a stand-in for the total length of wire and thus the number of windings wrapped around the polepieces. This defines the output and tone of the pickup in several key ways. The more windings there are, the more wire there is coiled around the magnet, within which the magnetic field changes induce voltage and current. This directly impacts the output of the pickup. However, the more windings there are, the more wire there is, and that increases DC resistance which reduces current flow and thus output across all frequencies. Also, the more coils there are, the higher the pickup's inductive reactance, and inductive reactance presents higher impedance (resistance to AC current flow like audio signals) to higher frequencies. That ultimately means a pickup with more windings produces more overall output concentrated in the midrange frequencies, as low and high frequencies are attenuated to offset the overall output increase. In addition, different gauges of wire can be used. The thicker the wire, the lower the DC resistance per foot, however the more volume it will take up around the bobbin, and so coils further from the magnetic field will be affected less (magnetic strength, like most forces, follows the inverse-square law; the strength of the force decreases on the square of distance, so small changes in distance matter quite a bit). So, given the same number of windings, a pickup wound with slightly thicker wire will have slightly lower output, more lows, about the same highs.
The number of coils in one pickup obviously matters. Humbuckers have a little less than double the wire of single coils, double the magnets/polepieces, etc, so they produce more output, but the magnetic field is broader, so shorter-wavelength harmonics act over different regions of the pickup and are cancelled out. Single-coil pickups thus tend to sound brighter and more articulate than humbuckers because their magnet and coil captures the vibrations of the string with less innate cancellation.
The placement of the pickup also obviously matters. Pickups closer to the middle of the string get much more of the fundamental frequency and more overall output (because they are over the portion of the string moving the most), while pickups closer to the bridge get more higher harmonics and less output because they're closer to the tethered end. Pickups intended for bridge placement are typically "hotter" to compensate for this, increasing their output while attenuating the highest harmonics.
Those are just the variables inherent in the pickup itself, with the most direct effect on the pickup's perceived loudness when installed in the same position on the same guitar and played by the same person through the same amp at the same gain/volume settings. The pickup that will sound loudest is the pickup that produces the highest output in mV after compensating its resonant peak (ideally the entire response curve) to the human equal-loudness curve. A pickup producing 3V peak output at a 6kHz resonant peak is not going to sound as loud as a pickup producing half the output with a resonant peak closer to 3-4k (the average peak of human hearing sensitivity).
Therefore, the two most fundamental measurements for perceived output are output in mV and resonant peak in Hz/kHz. If you don't have these, you're just guessing in a comparison between any two coils for relative output. Even then, output is just one variable in the overall sound of the pickup; the traditional passive guitar circuit is essentially an RLC band-pass filter circuit. You can nudge the actual resonant peak one way or the other by changing the capacitor and pot values in the tone circuit. The higher the pot value, the sharper the peak (at full tone of course), while the higher the capacitor value, the lower the frequency of the peak.
