Why didn't I think of this when I was in school

[Folkcafe]

Given the last few days reading materials, I couldn't help but kind of get a chuckle out of this one. I found this IEEE publication of lofty scholarly work from a couple of guys (brothers I think) from a french school. At the time, it really didn't contain what I was looking for, but I downloaded it anyway figuring I would skim it later for context.

Please have a look. Pick it apart. Perhaps you too might get a chuckle from it. If for nothing else by the way the introduction is written.

It is titled: Calculation Method of Permanent Magnet Pickups for Electric Guitars

HAL :: Accueil

If the page comes up in french, just select english in the drop down box on the top.

I truly hope you find this more entertaining than my misadventures of late.

[Joe Gwinn]

Aside from the fact that English is not their native language, I have the feeling that the brothers were in over their heads and so ended up using a fairly convoluted method. Nor is it true that finite-element methods won't work for such a geometry. They would have saved much time if they had found someone who knew a bit more electromagnetics to help with the analysis.

As for the "coulombian model", this is a fancy way to say that all velocities are a tiny fraction of the speed of light, so that quasi-static changes in magnetic potential are adequate to solve the problem. In other words, the variable-reluctance model.

However, their conclusion that the main source of pickup-caused harmonics is the nonlinearity of the magnetic field strength as a function of string position is correct.

[Folkcafe]

After reading papers like "Dynamic Compaction of Metal Particulates" this one certainly was a different kind of read. I don't ever recall seeing guitar publications in the references of a science paper before. Struck me funny.

I also found the same subject out of Princeton at http://www.physics.princeton.edu/~mc..._77_148_09.pdf If anyone is interested in comparison.

[bbsailor]

Aside from the fact that English is not their native language, I have the feeling that the brothers were in over their heads and so ended up using a fairly convoluted method. Nor is it true that finite-element methods won't work for such a geometry. They would have saved much time if they had found someone who knew a bit more electromagnetics to help with the analysis.

As for the "coulombian model", this is a fancy way to say that all velocities are a tiny fraction of the speed of light, so that quasi-static changes in magnetic potential are adequate to solve the problem. In other words, the variable-reluctance model.

However, their conclusion that the main source of pickup-caused harmonics is the nonlinearity of the magnetic field strength as a function of string position is correct.

Joe,

My own analysis comes to a much simplier reason for harmonic nonlinearity.

Assume that a scope is attached to a pickup to reveal a positive signal when the string in moving downward toward the pickup's magnetic field.

The distance between the string and the magnetic field varies between the lower movement where the field is stronger and upward where the field is weaker. There will always be an asymmetrical wave form with the movement toward the magnetic field being higher. Look at any conventional guitar pickup where the magnetic field is under the string to see this in action. As the pickup is moved farther from the strings this asymmetry is reduced but is still there.

Other forms of harmonic distortion occur because strings are sampled at different locations and the string positions for the fundamental and harmonics may be working more in phase or more out of phase depending on the pickup aperature width, number of active pickups and location of the pickup nodes on the string being played for a particular note.

Joseph Rogowski

[Joe Gwinn]

Joe,

My own analysis comes to a much simpler reason for harmonic nonlinearity.

Assume that a scope is attached to a pickup to reveal a positive signal when the string in moving downward toward the pickup's magnetic field.

The distance between the string and the magnetic field varies between the lower movement where the field is stronger and upward where the field is weaker. There will always be an asymmetrical wave form with the movement toward the magnetic field being higher. Look at any conventional guitar pickup where the magnetic field is under the string to see this in action. As the pickup is moved farther from the strings this asymmetry is reduced but is still there.

I think we are saying the same thing in different words.

Other forms of harmonic distortion occur because strings are sampled at different locations and the string positions for the fundamental and harmonics may be working more in phase or more out of phase depending on the pickup aperture width, number of active pickups and location of the pickup nodes on the string being played for a particular note.

I don't think aperture differences cause true distortion, which requires the generation of frequencies not in the original signal (versus selective removal of frequencies that were in this same original signal). Think linear as in linear system theory.