cutting posts?

[black_labb]

just out of curiousity, has anyone tried putting the screw in upside down (so the threads are closest to the string and the head tightens against the baseplate. was considering trying that for a pup i just installed on a build, but decided to do some work on the instruments set up instead. would be easily reversible which is always nice.

[Mike Sulzer]

They look the same to me outside of the black tape. What am I missing?

If I put the latest plot in Illustrator and cover the poles with 1/8" wide white rectangles, I see a very significant difference between the two. The field from the smaller pole spreads out faster. It is interesting that only 3/32" above the poles the field strength is nearly the same, although the spatial gradient is not. The flux emerging from the outer sides of the poles is a bit different near the top as well.

[Mike Sulzer]

I'm not sure I buy this. Does Dr. Meeker agree?

I have not asked him. It is not clear whether the limitations I see are in the actual calculatons or in the display, but I do suspect the latter. I am currently stuck using version three on my Mac because Crossover does not work with version 4. (In version 4, "drag and drop" is used from the materials library; this fails with crossover. It should get fixed eventually.) Version 4 allows dumping the data out in Matlab format. I am not a Matlab user (when I can avoid it), but I would read the Maatlab files in my own software. Then I could subtract the fields from measuring the "string" in two positions and see how noisy the difference is.

[Mike Sulzer]

If you are only thinking of the string as a magnet, you are missing the permanent magnet's field shape and how the moving string interacts with the lines of flux.

What is the physical basis for saying that the string interacts with the lines of flux of the permanent magnet anywhere except where the string is?

[Mike Sulzer]

Why is one blade thinner? If that's to simulate the screw vs. slug, it's missing the screw's head, which is the same diameter as the slug.

This was just to keep it simple at first. It is a good idea to add that; I think it will make the two sides more nearly the same, but we shall see.

[David Schwab]

What is the physical basis for saying that the string interacts with the lines of flux of the permanent magnet anywhere except where the string is?

I'm saying that by removing the pickup's magnet and using a small magnet on the string you are not simulating how that pickup works.

[Mike Sulzer]

I'm saying that by removing the pickup's magnet and using a small magnet on the string you are not simulating how that pickup works.

I did not say to remove the magnet, but rather to turn off the strong static field. One wants to leave the magnetic material in place since it can matter if it has significant permeability, such as alnico does.


But you said this "If you are only thinking of the string as a magnet, you are missing the permanent magnet's field shape and how the moving string interacts with the lines of flux." What does the permanent field do in addition to magnetizing the string? Since we have discussed this several times in the past, you know I think that is its only function. You do not agree, but have not shown that there is an additional function. Can you do this? What is the physics?

[David Schwab]

Can you do this? What is the physics?

Even if I don't know the reason behind something, I can hear the difference. You can demonstrate it for yourself. Remove the magnet from a pickup (and I mean something with more parts than a fender single coil), and now suspend the magnet over the strings. Does it sound the same? Why not? The strings are still magnetized by the field, so in your mind it will sound the same.

I can also reefer you to the two Bartolini patents, which discuss the shape of the field and its effect on the tonality of the pickup.

[Mike Sulzer]

Even if I don't know the reason behind something, I can hear the difference. You can demonstrate it for yourself. Remove the magnet from a pickup (and I mean something with more parts than a fender single coil), and now suspend the magnet over the strings. Does it sound the same? Why not? The strings are still magnetized by the field, so in your mind it will sound the same.

From my previous post: "I did not say to remove the magnet, but rather to turn off the strong static field. One wants to leave the magnetic material in place since it can matter if it has significant permeability, such as alnico does."

One can do these things in models.

I can also reefer you to the two Bartolini patents, which discuss the shape of the field and its effect on the tonality of the pickup.

As I recall, one of those patents is the one where Bartolini claims that a normal pole shape is sensitive to both vertical and horizontal string vibration, while his pole shape makes the pickup less sensitive to the horizontal. When we last discussed this, I showed that a normal pickup is not very sensitive to horizontal vibration. I showed two things:
1. The static field varies much faster in the vertical than horizontal direction.
2. The angular pattern of the field from the string is broad, and therefore the flux through the coil changes little from moving in the horizontal.

As I recall, you even agreed.

On the other hand, I have not claimed that the shape of the pole piece does not affect the tone of the pickup. The field and its gradient at the string can be affected. This is where one expects the permanent field to be important because it affects how the string is magnetized as a function of its position when it vibrates.

Another thing: You and your buddies accuse me of arguing. But you bring up the same thing repeatedly. You write the same things without addressing what I have written, even in a post from a short time ago. That is arguing. Enough.

[David Schwab]

Me and my buddies? A lot of people who come here also go to MIMF. Has nothing to do with any buddies I do or don't have.

And I'm not arguing with you, and telling you your tests are incomplete and don't really correlate to the real world.

If you really want to see what cutting the screws flush with the back of the baseplate does to the tone, just try it out. Or build a pickup with a more efficient magnetic structure and see how that sounds.

People who have tried it said the screw coil gets louder. Without trying it you tried to explain how that wouldn't happen, and since it does happen, your model is flawed.

So I suggested you over looked the importance of the whole magnetic circuit.

No one is arguing, except the people who have tried it and found that cutting the poles flush with the magnet does make the circuit more efficient. Even Seth Lover pointed that out.

So I say try it first, and then figure out why.

[Joe Gwinn]

If I put the latest plot in Illustrator and cover the poles with 1/8" wide white rectangles, I see a very significant difference between the two. The field from the smaller pole spreads out faster. It is interesting that only 3/32" above the poles the field strength is nearly the same, although the spatial gradient is not. The flux emerging from the outer sides of the poles is a bit different near the top as well.

It's true that the lines of force don't quite match, but I don't know how significant it is. Better would be to difference the magnetic potential plots about the line of (almost) symmetry.

Or to compute the integrated flux. I think I recall that FEMM will compute total flux crossing arbitrary boundaries.

[Mike Sulzer]

It's true that the lines of force don't quite match, but I don't know how significant it is. Better would be to difference the magnetic potential plots about the line of (almost) symmetry.

Or to compute the integrated flux. I think I recall that FEMM will compute total flux crossing arbitrary boundaries.

I think it is significant. Take a look at this plot, zoomed in. I think the program does a really good job of solving the diff eq., and you can see how it gets boundary conditions right.

http://www.naic.edu/~sulzer/bladeHumZ.png

[Mike Sulzer]

Now we can look at the effect of extending the narrower pole piece downward. The resulting plot is here: http://www.naic.edu/~sulzer/bladeHumExtended.png. The red line is a contour; the vertical component of the B field along this contour is shown here: http://www.naic.edu/~sulzer/extendedVsFlush.png. Also shown on this plot is the field along the same contour for the case where the pole is flush with the bottom of the magnet. The fields are quite different at the bottom, as they must be. But near the top of the poles and in the space above the pole, the two cases are almost exactly the same.

[Joe Gwinn]

I think it is significant. Take a look at this plot, zoomed in. I think the program does a really good job of solving the diff eq., and you can see how it gets boundary conditions right.

http://www.naic.edu/~sulzer/bladeHumZ.png

It looks the same to me, the first order, when you put the black tape over the two poles. I guess we need to discuss what "significant" means. More to the point, we need to hang a number on it.

[Joe Gwinn]

Now we can look at the effect of extending the narrower pole piece downward. The resulting plot is here: http://www.naic.edu/~sulzer/bladeHumExtended.png. The red line is a contour; the vertical component of the B field along this contour is shown here: http://www.naic.edu/~sulzer/extendedVsFlush.png. Also shown on this plot is the field along the same contour for the case where the pole is flush with the bottom of the magnet. The fields are quite different at the bottom, as they must be. But near the top of the poles and in the space above the pole, the two cases are almost exactly the same.

OK, but why does it matter?