Is it possible to accurately describe the tone of magnets and/or pickups?

[Mike Sulzer]

(1) Then you do not understand how physics and science in general work. This is not to say that scientists are not wrong sometimes. When they are, it is usually some very complicated consequence of general laws, something that seems intuitively right, but fails when the consequences of the law are fully computed. You appear to be exploring an E&M phenomenon that is a violation of Maxwell's equations: a hysteresis effect from a tiny field caused by a medium that interacts weakly with magnetic fields.

(2) Physics is necessary to understand pickups. The principles of EE are used to analyze the derived circuit.

(1) I am not sure how you can claim that something is impossible when you haven't tried it. I have been working with these materials for years, have several issued patents that cover their use as pickup components and external tone modifiers, and offer pickups on my website that use them to modify tone in the way that you claim is impossible.

You appear to be well-versed in basic EE principles (2) but fail to realize that there are aspects of tone generation in a pickup cannot be fully described using these concepts.

[Antigua]

I am not sure how you can claim that something is impossible when you haven't tried it. I have been working with these materials for years, have several issued patents that cover their use as pickup components and external tone modifiers, and offer pickups on my website that use them to modify tone in the way that you claim is impossible.

You appear to be well-versed in basic EE principles but fail to realize that there are aspects of tone generation in a pickup cannot be fully described using these concepts.

Have you solely relied upon your sense of hearing to confirm the phenomena you describe?

[Helmholtz]

Losses that result from the interaction of currents in the individual turns of the coil. These losses vary with scatter, overlap and tension of the windings and are typically greater in hand-guided vs machine-guided coils.

It is not clear to me what nonlinear effects you are referring to. Capacitance between turns and the proximity effect are linear phenomena that do not produce harmonics, though they introduce additional frequency dependancies.

[Tone Cam]

(2) You have claimed to have made a material with low conductivity and permeability. Therefore it interacts very little with magnetic fields. You are claiming that very small changing feeds cause significant hysteresis effects in a material with little interaction with those fields. That does not happen.
.

I am not sure how you can claim that something is impossible when you haven't tried it. I have been working with these materials for years, have several issued patents that cover their use as pickup components and external tone modifiers, and offer pickups on my website that use them to modify tone in the way that you claim is impossible.

You appear to be well-versed in basic EE principles but fail to realize that there are aspects of tone generation in a pickup cannot be fully described using these concepts.

[Tone Cam]

While I generally agree that nonlinear effects (and consequent cross-modulation of frequency components) in PUs tend to be underrated, I wonder what you mean by "nonlinear wire losses"?

Losses that result from the interaction of currents in the individual turns of the coil. These losses vary with scatter, overlap and tension of the windings and are typically greater in hand-guided vs machine-guided coils.

[Helmholtz]

Sorry, I didn't intend to restart a discussion about the Alumitones.

[Mike Sulzer]

(1) There are no significant nonlinear wire losses. Although the core does cause frequency dependent losses, there is no significant nonlineaerlity from the coil. The changes in field are tiny and hysteresis is not an issue; this is why you need so many turns on the coil.

(2) You have claimed to have made a material with low conductivity and permeability. Therefore it interacts very little with magnetic fields. You are claiming that very small changing feeds cause significant hysteresis effects in a material with little interaction with those fields. That does not happen.

(3) These things affect the inductance and resistance.

(4) The ear-brain system does not care how the ratios of harmonics in the signal were generated, and the filtering effect of the resonance has a large effect on the levels of harmonics in and/or near to the frequency range where this system has the greatest sensitivity.

Impedance measurements are easy to perform but provide limited info on some of the physical mechanisms that are important contributors to pickup tone. I don’t see how an impedance measurement is going to provide much info on the (1) nonlinear core and wire losses that are significant sources of harmonic generation in a pickup.

Impedance effects cannot explain the significant (2) tone-modifying effects of a ¼ inch wide x 1/32 inch thick, unmagnetized strip of insulator bound alnico granules that is taped to the outside surface of a humbucker coil. In this position it adds hysteresis loss to the magnetic circuit that is formed by the pickup and strings but does little else.

(3) Impedance measurements also provide very little info on the changes in pickup tone that are associated with variations in wire tension, insulation type and scatter in the coils.

I think it is an oversimplification to claim that the pickup-cable resonance is the 'most important factor' in determining pickup tone. (4) Pickup cable resonance does not generate harmonics - it filters them. Nonlinear loss processes, including hysteresis, eddy currents, anomolous ferromagnetic losses and proximity losses in the coils, are harmonic generators. The time dependent spectrum of the signal that gets to an amp is determined by the harmonics that are generated by the pickup and the filter characteristics of the circuit that includes the pickup, tone circuit, and cable.

[bbsailor]

The principle described is called the "Eddy current brake". You always have both, the "back magnetic force" as well as energy absorption in the conductor. In PUs the load is usually high impedance, not allowing for noteworthy current. So the string motion damping effect is practically non-existent. But e.g. Alumitone PUs have a closed, very low resistance massive aluminum loop close to the strings, so some string motion damping effect is conceivable. But don't forget that the magnetic fields involved with PUs are very small.

Once you understand how the Alumitone pickup works, you may see how some trade-offs between what you said about "eddy currents" in the string loop directly below the strings and the lower DC resistance in the two coils below the frame affect the tonality of the audio output. The metal frame is the very low impedance single turn string loop with the transformer lamination intersecting the metal frame in the location where the currents from both coils are common (adding). Thus, the induced current in this aluminum frame are primary current of a current transformer with two approximately 15000 turn coils wired in parallel for an effective turns ratio of about 1 to 7500. This is about the amount of turns on a conventional high impedance guitar pickup but with one big exception.

This exception is that guitar pickups have a single turn loop length that is twice the string width plus the radius of the end turn. If a pickup has a 2 inch string width, the straight length of the wire is 4 inches. The end turns are the diameter of the magnet core times 3.14159 to account end turn length. The two coils under the Alumitone frame are round and thus do not need the straight wire length so they are 4 to 5 time shorter with the same amount turns but induced by the current in the frame converted by the transformer action of the two parallel wired coils under the frame.

This Alumitone design now allows the tone of the pickup to be determined by the relationship of the very low resistance primary string loop relative to the amount of the turns of the high turns secondary coils to form the effective turns ratio of this transformer based pickup (much like a low level current transformer). Search "low impedance Pickup research" on this forum to see more details.

This is a prime example where trade-offs in design by minimizing the DC resistance of the secondary coils wire; the magnetic coupling of the metal frame to the two secondary coils; and the magnetic coupling to the strings creates a new set of variables to consider when analyzing pickup response and quality control for manufacturing many products with consistent results. Since the primary string loop is directly under the strings generating the current in the transformer primary, the output for this transformer action is much more efficient than a traditional high impedance pickup where the voltage induced in the pickup turns is more in the upper coil turn location and less in the lower coil turn location along with about one fourth to one fifth less DC resistance.

The bottom line is: today's high impedance pickups represent a 1930's technology that has not evolved much until more modern active pickups and Alumitone transformer-based type pickups have become available. It is now time to seek to better understand these new designs and relate their understanding to what we still build today. Magnets and induction are still involved but the evolutionary changes requires a more comprehensive understanding of the interaction of all the variables to the sound we characterize as "good".

Joseph J. Rogowski

[Helmholtz]

I know this exchange was from a long way back, but I've been lurking on this thread since the beginning, and have been trying to follow along. So bear with me. I just stumbled across this youtube video Copper's Surprising Reaction to Strong Magnets | Force Field Motion Dampening and wondered if this played a part in some of the observations we've made. This is what I'm thinking:

At one point in the video there's a demonstration that a conductor moving relative to a magnetic field produces an electric current (whew! glad that's still true). The surprising twist to me was that if the current is not drawing energy out of the interaction, ie, if the coil is shunted, there is a "back magnetic force" (magnetic impedance? please let me know the actual term) that resists the relative motion. In this video, about 2:24 in, the magnetic object slows down its relative motion when the coil generates current. My takeaway from this is that since the pickup magnet->string->coil->tone/volume controls circuit is not 100% efficient at transducing the energy, there is some resistance to magnetized string motion by the coil. Is this something that's just painfully obvious to everyone but me?

edit: after some thinking, I know the shunted winding thing is true of other magnetic drivers such as speakers and permanent magnet motors, so I guess I shouldn't be too surprised to see it here. I guess I never thought that it may affect string mechanics.

The principle described is called the "Eddy current brake". You always have both, the "back magnetic force" as well as energy absorption in the conductor. In PUs the load is usually high impedance, not allowing for noteworthy current. So the string motion damping effect is practically non-existent. But e.g. Alumitone PUs have a closed, very low resistance massive aluminum loop close to the strings, so some string motion damping effect is conceivable. But don't forget that the magnetic fields involved with PUs are very small.

[eschertron]

An immobile fixed magnet cannot produce a damping effect. It just acts like an ideal spring attached that absorbs and releases the same amounts of energy. This follows from the law of conservation of energy. Things change when eddy current effects are involved.
(I do have a scientific background.)

Could position of the magnet along the vibrating string length (other than center that is) create a dissonant, and therefor damping vibrations along the strings length? I'm thinking of a problem that is typically called Stratitis. Said to be caused by excessive magnetism due to pickups being adjusted too close to the strings. It causes odd harmonics and damping of sustain is usually reported.

I know this exchange was from a long way back, but I've been lurking on this thread since the beginning, and have been trying to follow along. So bear with me. I just stumbled across this youtube video Copper's Surprising Reaction to Strong Magnets | Force Field Motion Dampening and wondered if this played a part in some of the observations we've made. This is what I'm thinking:

At one point in the video there's a demonstration that a conductor moving relative to a magnetic field produces an electric current (whew! glad that's still true). The surprising twist to me was that if the current is not drawing energy out of the interaction, ie, if the coil is shunted, there is a "back magnetic force" (magnetic impedance? please let me know the actual term) that resists the relative motion. In this video, about 2:24 in, the magnetic object slows down its relative motion when the coil generates current. My takeaway from this is that since the pickup magnet->string->coil->tone/volume controls circuit is not 100% efficient at transducing the energy, there is some resistance to magnetized string motion by the coil. Is this something that's just painfully obvious to everyone but me?

edit: after some thinking, I know the shunted winding thing is true of other magnetic drivers such as speakers and permanent magnet motors, so I guess I shouldn't be too surprised to see it here. I guess I never thought that it may affect string mechanics.

[bbsailor]

The vertical string motion alone produces significant second harmonic content (around 25% according to Zollner), as the vertical magnetic field above the PU is not homogeneous but decreases approximately according to 1/d², d being the distance between string and polepiece.

Yes, and this is why the observed oscilloscope image of a guitar string pluck is asymmetrical because as the string moves down toward toward the pickup magnet, it produces a higher output than the upper movement farther away from the pickup magnet with a lower output.

Joseph J. Rogowski

[Helmholtz]

Mikes comments are all valid but one of his statements gets very little attention in these discussions "the frequency doubling resulting from string motion parallel to the face of the pole piece". Horizontal string motion relative the the pole piece face and coil face plane induces more second harmonics than a more vertical motion which emphasizes the fundamental frequency.

The vertical string motion alone produces significant second harmonic content (around 25% according to Zollner), as the vertical magnetic field above the PU is not homogeneous but decreases approximately according to 1/d², d being the distance between string and polepiece.

[Helmholtz]

I don’t see how an impedance measurement is going to provide much info on the nonlinear core and wire losses that are significant sources of harmonic generation in a pickup.

While I generally agree that nonlinear effects (and consequent cross-modulation of frequency components) in PUs tend to be underrated, I wonder what you mean by "nonlinear wire losses"?

[bbsailor]

In reference to the bolded statement: Impedance measurements characterize the pickup-cable resonance, and this is without doubt the most important factor in determining the tone of the pickup. They can even describe the deviations from the two pole resonance of a simple linear circuit, that is, the more subtle effects introduced by the frequency dependent losses due to eddy currents.

I have not been able to get access to the full text of the paper you cite, but the abstract indicates that it presents an analysis using the law of magnetic induction and calculates in detail that the response is nonlinear. The well known causes of this nonlinearity are the nonlinear part of the variation of the flux through the coil resulting from the change in distance of the string, the frequency doubling resulting from string motion parallel to the face of the pole piece, and the variation of the strength of the permanent field with distance from the magnet. I do not see any indication that hysteresis enters into this. The "minor loops" that you describe are extremely close to straight lines, and so I do not see how you get an effect from them.

Certainly materials such as you describe with low conductivity and permeability make a pickup with a higher resonance frequency and Q, and I think this would be very similar to using neo magnets with no additional pole piece. Neos are of course available in a vast range of sizes and shapes, and so the field strength variations and spatial variations due to magnet shape are easily produced. However, you seem to be describing changes other than those I mentioned, and I do not see what they can be.

Mikes comments are all valid but one of his statements gets very little attention in these discussions "the frequency doubling resulting from string motion parallel to the face of the pole piece". Horizontal string motion relative the the pole piece face and coil face plane induces more second harmonics than a more vertical motion which emphasizes the fundamental frequency. This effect can be highly subjective as it typically only occurs in the first 30 to 50 milliseconds after the string pick or strum. Instruments having pickups with two pole pieces per string emphasize this effect even more.

To add even more variables, look at the plectrum thickness; picking/strumming location relative to the active pickup(s); environment where we are playing; and developed picking/strumming techniques for its effect on the perceived sound. The sound of the pickup is an accumulative effect with some commonly understood effects of winding capacitance, guitar chord capacitance, resonance loading, eddy currents near pickup coil, pickup inductance and string window width being induced into the pickup coil(s).

Discussing any one of these in isolation does not do justice to the collective interaction of all of these to the perceived outcome.

Joseph J. Rogowski

[Tone Cam]

In reference to the bolded statement: Impedance measurements characterize the pickup-cable resonance, and this is without doubt the most important factor in determining the tone of the pickup. They can even describe the deviations from the two pole resonance of a simple linear circuit, that is, the more subtle effects introduced by the frequency dependent losses due to eddy currents.

Impedance measurements are easy to perform but provide limited info on some of the physical mechanisms that are important contributors to pickup tone. I don’t see how an impedance measurement is going to provide much info on the nonlinear core and wire losses that are significant sources of harmonic generation in a pickup.

Impedance effects cannot explain the significant tone-modifying effects of a ¼ inch wide x 1/32 inch thick, unmagnetized strip of insulator bound alnico granules that is taped to the outside surface of a humbucker coil. In this position it adds hysteresis loss to the magnetic circuit that is formed by the pickup and strings but does little else.

Impedance measurements also provide very little info on the changes in pickup tone that are associated with variations in wire tension, insulation type and scatter in the coils.

I think it is an oversimplification to claim that the pickup-cable resonance is the 'most important factor' in determining pickup tone. Pickup cable resonance does not generate harmonics - it filters them. Nonlinear loss processes, including hysteresis, eddy currents, anomolous ferromagnetic losses and proximity losses in the coils, are harmonic generators. The time dependent spectrum of the signal that gets to an amp is determined by the harmonics that are generated by the pickup and the filter characteristics of the circuit that includes the pickup, tone circuit, and cable.