Hi, Sylvester. I was wondering about this a few years ago and did a little research. I'm pretty lo-tech and four years new to electric guitars. This article seemed sensible and useful to me, including the referral to pup-master Lindy Fralin's website for more info:
MEASURING PICKUP PERFORMANCE[1]Because impedance and resistance are both measured in Ohms, people often confuse the two. Though they both can be thought of as a restriction on the flow of electrons through a circuit, thus being measured in units of resistance, they are not the same. Impedance is a phenomenon that most markedly affects AC circuits, when the magnetic field induced in a wire by the flow of current, impedes (or "chokes") the flow in a wire running parallel and adjacent to it. A coil puts the wire in parallel and adjacent to itself, over and over again, allowing the magnetic field of each wrap to "choke" the current in each adjacent wrap. That's why you see coils sometimes referred to as "chokes".
An ohm meter will only measure DC resistance, which remains constant over a particular length of wire, whether it's stretched out straight, or wrapped around a bobbin.
The factor we are really interested in is inductance, which is measured in Henrys. Inductance happens when the movement of a magnetic field causes (induces) a flow of current in a wire. That's what happens when you pluck the strings of an electric guitar. The magnetic field around the pole-pieces is disturbed (moved around) by the vibrating wire string, inducing an AC current in the coil (the signal).
The reason DC resistance is used to compare pickups, is because it's the easiest thing to measure. If the NECK and BRIDGE pickups both use the same bobbins, magnets, pole-pieces, and wire (I don't know if Mustangs do), DC resistance will give you an indication of the variation in inductance. More resistance = longer wire = more wraps around the bobbin = more inductance = a "hotter" pickup.
If your bridge has about twice the DC resistance, compared to your neck, you can surmise that it has about twice the length of wire and thus, about twice as many wraps around the bobbin.
Does this mean it has twice the inductance? Sort of. As the wrapping progresses, the wraps get further and further from the magnetic core and the wire length of each wrap gets longer. If the wraps are not uniform, you introduce another variable; if one magnet has more Gauss (the unit of magnetism), that becomes another variable. That’s why there's all the "abouts" in the above paragraph.
At best, DC resistance is a very rough way of comparing two similarly constructed pickups. You can't compare Humbuckers to P-90's, or P-90's to Fender single-coils. Or any of these to PAFs. The classic Mustang pups are 5.5kΩ, or "kilohms".
Theres :
Ω (ohms)
kΩ (kilohms)
MΩ (Megohms)
Standard (1960s to early 1970s) Mustangs pickups are wired in parallel and if each pickup is 5.5kΩ and you have both on you are cutting the resistance (but not the volume) by half to 2.5kΩ... but if they were wired in series you would be doubling the output (K) to 11kΩ but the volume doesn't double.
A humbucker is two single coils wired in series, each coil can be as low as 4kΩ but because there's two in series it makes 8kΩ.
Whether two pickups are wired in series or parallel is irrelevant as to whether they will be humbucking or not. Providing one pickup is RWRP (reverse wound/reverse polarity) to the other pickup they will cancel hum regardless.
So, resistors or K (which include pickups and potentiometers) in series doubles the value and in parallel it halves the original value.
-From Bandit, Nov. 24, 2009 on the Jag-Stang website forum.
Re: Pups' resistance; Sent: Mon Nov 23, 2009 6:18 am; From: feedbackismyfriend
Ya I just got back from an absolutely wonderful weekend. To be honest, I have a pretty minimal knowledge of how pickups work. The "k" is put after the measurement of resistance and I'm not really sure if that is just a symbol or if it refers to a thousand (IE: 12k=12,000). Also, I believe that ohms is the correct term, but I'm not really 100% sure.
As far as how a pup's rating affects its tone, in general a higher rated pickup has more output and is more responsive to midrange frequencies (thus being able to drive your amp quite a bit harder), but tend to suffer a bit in their responsiveness to bass and treble frequencies. Lower rated pup is pretty much exactly the opposite; it has less output, but is much more responsive to bass and treble frequencies (they tend to suffer a bit in the midrange area though).
Also, how the pickup is constructed and what kind of material is used for the magnet affects the tone a lot, It's not just about the pickups' rating. As far as sites go, I would recommend checking out Lindy Fralin's website. Lindy Fralin is a very highly regarded pickup manufacturer and I found their site to be quite informative. -Glenn
[1] Note: the original pickups on a 1965 Mustang are typically about 5.5 K, or ohms.
