In our testing of every pickup before it is shipped, we use a mechanical "picking tester". This device picks a short length of plain string (0.017 inch diameter) in a very repeatable manner. Testing with the "picking tester" has yielded some interesting results.
In the following measurements:
- Distance A is the initial distance from the string to the pickup surface
- Distance B is the distance at which the picked output is reduced to half of its original value
- A-B is the difference needed to reduce the picked output to half of its original value
- Thickness is that of the magnetic structure of the pickup itself. For example, in a Fender J pickup this thickness is the vertical length of the Alnico magnets
- F is the difference (A-B) needed to reduce the signal by half, as a percentage of the thickness of the magnetic structure of the pickup.
|Type of pickup||A distance||B distance||B-A||Thickness||F|
|traditional Alnico polepiece J-Bass*||0.140"||0.280"||0.140"||0.750"||19%|
|iron + vertical ceramic magnet s.coil||0.140"||0.280"||0.140"||0.580"||24%|
|iron + horizontal ceramic magnet d.coil||0.140"||0.240"||0.100"||0.580"||17%|
|iron + horizontal ceramic magnet d.coil||0.140"||0.220"||0.080"||0.320"||25%|
|average F 21%|
So, if you raise the string away from the pickup by 20% of its thickness you will lose half the signal. If it is a thin pickup, like our 5J jazz guitar pickup, it takes less than a little more than 1/16" to lose half the signal but still, approximately 20% of the pickup thickness. The above 4 examples are vastly different magnetic structures, but the way in which the magnetic field interacts with the string remains approximately the same.
A humbucker that is tilted so that one edge is much further away from the string than the other will have much lower output and thinner tone, closer to that of a single coil. This is because it is mostly the coil that is nearest the string that is doing the sensing.
To control the pickup tilt to provide equal sensing from both coils of a humbucker, the pickup should be mounted to the instrument with either 3 or 4 screws. These screws should be adjusted so that the pickup top surface is parallel to the underside of the strings when the strings are depressed at the 12th. fret.
It can be difficult and tedious to do this with pickups that have only 2 mounting holes. The pickup must be installed and removed several times while hunting for the "right" piece of foam that will push up on the bridge side of the pickup by the "right" amount, which will change as the foam ages and dries out... In a pinch one can wedge matchbook covers, etc. between the pickup and the wood to hold the pickup in place to get through the next practice session or gig...
We drill the mounting holes after we finish the epoxy process so that we can drill for 3 mounting screws when possible and for 2 mounting holes when it isn't.
There are combinations of pickup shapes, coil choices and string widths that leave no choice except to drill for only 2 mounting screws.
But whenever possible, the pickup mounting should allow good control over the tilt of the pickup under the string.