Slugs: Which is more important - Diameter or Mass?

[Diablo]

The main thesis of the above referenced patent is that the hollow core presents less direct downward pull on the strings and thus allows the string to vibrate longer.

Joseph Rogowski

Does anyone else here besides me think this patent makes no sense whatsoever? Anyone can get a patent if they pay $. It doesn't mean the patent actually does what is claimed.

[Possum]

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the patent makes total sense, you don't have a solid core conducting the flux, but hollow tubes which will obviously conduct less, not hard to understand and easily provable with a gaussmeter. You could do something similar like DiMarzio does and put a spacer so the magnets don't directly contact the slugs or pole pieces as well, but I'm sure tubes will conduct less. Its a cool idea but if it was all that great you'd see more use of it, the patent could easily be gotten around by say filling the tubes with some substance and claiming special properties for it :-)

[Diablo]

I agree that the hollow core pole pieces will conduct less flux for the same strength magnet. But, the primary claim of the patent is that a hollow core arranges the flux pattern in some way different from a solid core, and the different flux pattern doesn't damp the string vibrations. Take a look at his "magic arrows" in the patent near the poles.

[Joe Gwinn]

Are eddy currents a bad thing or a good thing?

Both. Depends on context and intent.

Correct me if I'm wrong, but aren't the eddy currents generated by the changing field of the vibrating strings?

Yes.

Isn't the magnetic flux of the strings relatively weak? So, isn't the flux density in either the slugs or screw poles relatively weak? And wouldn't the eddy currents also be very weak?

Everything scales in strict proportion, including the music.

If eddy currents are a bad thing, couldn't you reduce them by making laminated poles in the same way they make motors and generators out of lamination stacks?

Absolutely. See Kinman's recent patents, and I think there have been knockoff patents as well. And aircore pickups (coil of wire around ceramic magnets in a plastic shell) are free of eddy currents.

Eddy currents do affect the tone of a pickup, and so are part of the method by which one achieves a desired tone.

[Diablo]

Both. Depends on context and intent.

Yes.

Everything scales in strict proportion, including the music.

Absolutely. See Kinman's recent patents, and I think there have been knockoff patents as well. And aircore pickups (coil of wire around ceramic magnets in a plastic shell) are free of eddy currents.

Eddy currents do affect the tone of a pickup, and so are part of the method by which one achieves a desired tone.

Thanks for the answers Joe. Could you describe the effect on tone with higher eddy currents vs lower eddy currents? In my other business, everyone wants eddy currents as low as possible and the permeability as high as possible. If one were to make a pickup with very low eddy currents and high permeability........would it sound better or worse than conventional pole materials? Has anyone already tried this?

[Joe Gwinn]

Thanks for the answers Joe. Could you describe the effect on tone with higher eddy currents vs lower eddy currents?

The higher the eddy currents, the greater the loss of highs, causing mids and lows to become more prominent. This can be good or bad depending on the tone without the eddy current loading

In my other business, everyone wants eddy currents as low as possible and the permeability as high as possible.

Why? What are they trying to achieve?

If one were to make a pickup with very low eddy currents and high permeability........would it sound better or worse than conventional pole materials?

Depends on what one is trying to achieve.

Define "better" and "worse". In what sense?

Define "conventional pole material". What other material is under consideration?

Has anyone already tried this?

Many times, in many variations.

[Diablo]

Quote:
In my other business, everyone wants eddy currents as low as possible and the permeability as high as possible.

Why? What are they trying to achieve?

Higher efficiency, coolest running, lowest cost motors and transformers. Generally, they don't care what they sound like, as long as they don't hear them.....
Quote:
If one were to make a pickup with very low eddy currents and high permeability........would it sound better or worse than conventional pole materials?

Depends on what one is trying to achieve.

Define "better" and "worse". In what sense?

Define "conventional pole material". What other material is under consideration?

Conventional pole materials are either steel screw poles or steel slug poles, and what Seth Lover refers to as "soft iron". From what I can tell, these conventional poles were/are produced with little or no consideration to magnetic properties. In addition, the magnetic properties of iron are highly structure sensitive, so I would expect to see a lot of variability in the magnetic properties of the conventional pole materials. Steel mills don't guarantee magnetic properties of bar products, not large producing mills anyway. What I am getting at is that the structure of the iron can be changed with proper heat treatment and composition to produce consistent magnetic properties. I'm just trying to understand if the same technology used in transformer steel to improve magnetic properties (much higher permeability and much lower eddy currents) can be applied to pole pieces in pickups. I think your answer was "it depends".

[Joe Gwinn]

Quote:
In my other business, everyone wants eddy currents as low as possible and the permeability as high as possible.

Why? What are they trying to achieve?

Higher efficiency, coolest running, lowest cost motors and transformers. Generally, they don't care what they sound like, as long as they don't hear them.....

Ah. Motors and transformers.

Quote:
If one were to make a pickup with very low eddy currents and high permeability........would it sound better or worse than conventional pole materials?

Depends on what one is trying to achieve.

Define "better" and "worse". In what sense?

Define "conventional pole material". What other material is under consideration?

Conventional pole materials are either steel screw poles or steel slug poles, and what Seth Lover refers to as "soft iron". From what I can tell, these conventional poles were/are produced with little or no consideration to magnetic properties. In addition, the magnetic properties of iron are highly structure sensitive, so I would expect to see a lot of variability in the magnetic properties of the conventional pole materials. Steel mills don't guarantee magnetic properties of bar products, not large producing mills anyway. What I am getting at is that the structure of the iron can be changed with proper heat treatment and composition to produce consistent magnetic properties. I'm just trying to understand if the same technology used in transformer steel to improve magnetic properties (much higher permeability and much lower eddy currents) can be applied to pole pieces in pickups. I think your answer was "it depends".

All of these things are true, and people used whatever came conveniently to hand to make pickups. The recipes that worked well (or very badly) are famous.

As for using transformer iron in pickups, there is no reason this wouldn't work, and people have done it. Also, people have used permalloys and the like. But a lot of people use plain old mild steel (~1018).

The point is to come up with a recipe that yields a sound one likes, consistently, at the least expense in time and to a lesser extent materials.


PS. The red was hard on my eyes, so I changed it to blue.

[Diablo]

Thanks Joe for your thoughts on the subject. I remember reading a Seth Lover interview where he said that the pickup works the same way as a generator or motor, and a light went off in my head. Better iron = better generator. But, I have to agree that consistently good tone is the goal and not maximum efficiency.

[David Schwab]

Bartolini used to make some guitar humbuckers with laminated steel blades. I think Possum here uses a laminated blade on one of his pickups.

Bill Lawrence (Willi Stich) uses stainless steel blades for the same reason. Obviously they are some form of SS that is magnetic.

Alembic pickups are wound around a ceramic magnet and no metal at all in the pickup.

Steel can be used to an advantage in warming up the tone.

[Mike Sulzer]

I agree that the hollow core pole pieces will conduct less flux for the same strength magnet. But, the primary claim of the patent is that a hollow core arranges the flux pattern in some way different from a solid core, and the different flux pattern doesn't damp the string vibrations. Take a look at his "magic arrows" in the patent near the poles.

If a particular pole piece geometry "pulls" less on the strings, then the string would be magnetized less, and the voltage output of the pickup would be less. So is hollow core idea just another way of making the magnet field at the string weaker? Any claim that you can make the field weaker and not lessen the output should be viewed with suspicion; one needs real analysis, not hand waving arguments. And why would this way of making the field at the string weaker be better than simply using a weaker magnet?

On another subject: Do regular shaped pole pieces pick up motion along the pole piece axis and perpendicular to it equally? (Bartolini) This also requires careful justification, not hand waving arguments, and I would not accept this without real analysis. This can be modeled with FEMM approximately, although one must remember that FEMM is not a true 3D modeler; it does two cases: 3D symmetrical about an axis (cylindrical), and 2D. One needs to use one or both of these modes and some careful thinking to get significant results with FEMM.

[David Schwab]

And why would this way of making the field at the string weaker be better than simply using a weaker magnet?

I've seen this patent, and never really thought much about whether it works or not. What it reminded me of was this pickup, which in itself seems a variation of the Fender P bass pole design:



And I've always thought this, being a "trembucker", was to stop the string from hitting the pole when you dive bomb, thus making a loud click. This is also patented. The patent (5148733) states:

The string of the string instrument passes over the pole piece in aligned relationship with the slot thereby allowing vibration in a zone which is substantially free of any intense magnetic flux lines.

The invention relates to the field of magnetic pickups for electric guitars, and more particularly, to an improved pole piece for an electric guitar having a configuration such that the magnetic field does not substantially interfere with the vibration of the string.
In the prior art, solid circular pole pieces have been used to direct the magnetic field from a permanent magnetic upward to the vicinity of a ferromagnetic guitar string. When the string is plucked, the vibrating string interacts with the magnetic field to cause changes in the paths of the flux lines. These changes occur at the same frequency or frequencies and intensity as the string vibrations. A coil wrapped around the pole piece generated a signal as the changing flux lines cut across the wires of the coil. This signal should have had all the frequency and intensity characteristics of the vibrating string if the string had been vibrating freely.

Unfortunately this was not the case. A freely vibrating guitar string has a very complex vibration pattern in the form of a precessing ellipse. The vibration has both primary and harmonic frequency components. Various characteristics of the vibration are important to good tonal quality in an electric guitar. Among the most important of these characteristics are: the length the vibrations lasts, i.e., the so-called "note sustain"; the richness (completeness) of the harmonic content reproduction; the accuracy of reproduction of the spectral content of the string vibration as the string is shortened or lengthened by pressing it against various frets on the fretboard; and, the reproduction of an "open" or "natural" sound.

The quality of the magnetic design of the pole piece in the guitar pickup has a great deal to do with whether or not these characteristics are achieved. If the pole piece is designed such that the guitar string passes through a significant portion of the magnetic field, the magnetic forces acting the guitar string will adversely alter the vibrational characteristics of the string. These forces dampens vibrations thereby reducing "note sustain". Further, the forces dampen certain harmonics more than others thereby altering the spectral content of the output signal. This adversely affects richness of the sound, the accuracy of note intonation and the "naturalness" of the sound.

And so on.


It also cites the above hollow pole patent in the prior art section, and they show three illustrations that seem to have been made placing iron filings on paper over the pickup. The solid pole picture is much different from the hollow and slotted poles.

One worker in the art attempted to solve this problem by making the pole piece a hollow tube made of ferromagnetic material. This design is detailed in U.S. Pat. No. 4,624,172 to McDougall. Unfortunately, the McDougall design did not completely solve the problem of string vibration dampening by the magnetic field of the pickup. Although the McDougall design did make some improvement over the solid pole pieces of the past, it has been discovered by the applicant that the McDougall design made surprisingly little improvement over the prior art.

Does it work? I have no idea. I have played the Trembuckers though and they have a very smooth tone.

[Diablo]

OK, let me take a stab at the analysis of a magnet and string. My analogy would be to think of a child on a swing. If you pull the swing back and let it go, the system keeps swinging forever in the absence of friction in the attachments. Gravity always tries to pull the swing closer to the ground, but it doesn't stop the swing from oscillating back and forth. It should be the same physics for a vibrating guitar string. When the string is on one side of the magnet pole, the pole pulls the string in one direction adding energy, and as the string vibrates away from the pole the magnetic force should remove the same amount of energy - net sum is zero. The only energy of the vibrating string is supplied by the original plucking. One thing that is different with magnetic attraction and gravity is that the gravitational attraction is constant on the swing. The magnetic attraction is stronger as the string nears the pole, however I can't see how this will change the outcome. I believe the magnet strength shouldn't effect the sustain. But, I'm willing to listen to other opinions if someone can point out the errors of my analysis.

[David Schwab]

Even without a magnet under the string, it will stop on its own due to friction, and the body also absorbs some of the energy.

You can verify that a pickup's magnet will indeed affect the vibration of a string... just adjust a Strat's pickups very close to the strings. Strat pickups will do it before a humbucker precisely because the rod magnets exert more pull that a humbucker, which has a rather low field. And blades seem to exert less pull than rod shaped poles.

If I put one of my neo bar magnets right under the string, it does stop it from vibrating.

[Diablo]

Even without a magnet under the string, it will stop on its own due to friction, and the body also absorbs some of the energy.

You can verify that a pickup's magnet will indeed affect the vibration of a string... just adjust a Strat's pickups very close to the strings. Strat pickups will do it before a humbucker precisely because the rod magnets exert more pull that a humbucker, which has a rather low field. And blades seem to exert less pull than rod shaped poles.

If I put one of my neo bar magnets right under the string, it does stop it from vibrating.

You are correct, and a little more googling explained where I went wrong.
I forgot about Lenz's law and the eddy currents. The relative motion between the string and the magnetic pole generates eddy currents in the string that have magnetic fluxes that oppose the movement of the string. So, it has nothing to do with the shape of the magnetic poles, but only the field strength seen by the string.

http://www.coolmagnetman.com/magplum.htm