How do stacked pickups work?

[Alex Shroyer]

Pickup makers sometimes offer "stacked" pickups as lower-noise alternatives to single coil pickups. I know technically they're humbucking, but since they look like single coils, marketing dictates they should have a different name.

I think I get the very basics of how they should work, but could help understanding some details. Here's how I think they work in broad strokes, please let me know if any of this is wrong (marked with (?) where I'm uncertain):

1. start with a normal single coil, magnet and pole pieces all normal (call this the "sense" coil S)
2. add another coil along the same axis as the pole pieces of the first (call this the "noise" coil N)
3. move the N coil farther away from the strings, possibly even outside the magnetic field (if you move it off-axis, you can call it a dummy coil)
4. wire S and N together, in series (?)

Wiring S and N together won't cancel noise unless (?)
a) they're wound in opposite directions and you connect the start of one to the end of the other, OR
b) they're wound in the same direction and you connect them either start-start or end-end

Then you (?) tweak the parameters of the N coil to cancel as much noise as you can without drastically affecting the tone you hoped to get from S.

Is that all correct?

[JC Whitney]

I think that this explanation [www.youtube.com/watch?v=ceCdXVP-mu8] paired with side view of a stacked at (time) 1:39 into this video [www.youtube.com/watch?v=5BqFoBJr10o] supports your understanding... in that in the [1:39] pickup the upper coil is larger to maximize its non-bucked signal, with the lower being just big enough to acceptably moderate the hum signal. Seems ripe for experimentation.

[Jarno Verhoeven]

In my opinion it is not just marketing, they do have different properties than a side by side humbucker so I guess it is helpful to differentiate the one from the other, and the coils are stacked on top of the other

[Alex Shroyer]

Glad to know I wasn't too far off base, thanks. I have a Gibson Blueshawk whose dummy coil still confuses me. The guitar has 2 single coil pickups, which are rw/rp so they cancel hum in the "both" position. But there's also a dummy coil that cancels hum when either pickup is used alone.

I had hypothesized that the optimal use of the dummy coil should have one polarity when combined with the neck pickup and the opposite polarity when combined with the bridge pickup. But then I took all the coils out of the guitar to compare all the wiring permutations and proved myself wrong! There's exactly one orientation of the dummy coil that works best with both pickups despite the sensing pickups having opposite polarities from each other.

The dummy coil is positioned both deeper in the body and midway between the neck and bridge pickups. Not sure if this placement - roughly where a middle pickup would go but farther from the strings - matters for hum canceling or not. There is at least one product (https://www.ilitchelectronics.com/hum-c ... g-systems/) that mounts in a control cavity. Ripe for experimentation indeed. I'll keep tinkering with dummy coils in my Blueshawk to see how hum-free I can make it without ditching the stock pickups.