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Post by ms on Feb 14, 2023 14:36:21 GMT -5
but the thing that makes the reluctance model appealing is that it automatically accounts for the contribution of the permeable core in the pickup, since you're looking at all the permeable elements at once, and how the sum reluctance between them changes when the guitar string is moving. I think that including the permeable core in the calculation of the reluctance difference is important and not easy.
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asher
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Post by asher on Feb 14, 2023 17:44:13 GMT -5
That is not what is expressed there.
On the left, we have maximum-flux-value for the dimensional material in question (here, the string); on the right side we have the maximum flux for the material (CO steel) multiplied by the effective area of the dimensional material.
Where are you suggesting that this happens in a guitar?
No. I am saying that the sign of the induced voltage changes as the string crosses the pole piece, and that the magnetic polarity of the string does not change.
Again: What math do you take this to correspond to? Where do you take the flux to be going?
Why are we not talking about V=N*dɸ/dt?
What is your math for the reluctance difference? Including the permeable core should be fairly straightforward, but I don't understand how this reluctance argument is being presented formally.
Could anyone please provide any links that elaborate on the whole picture of the reluctance argument, whether specific to guitar or not? That is, enough of a picture to assemble a mathematical description, even if it is of a toy context?
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Post by antigua on Feb 14, 2023 18:22:46 GMT -5
Regarding reluctance, it shares a lot in common with considerations of transformers eepower.com/technical-articles/magnetic-circuit-properties-understanding-reluctance/ if you think of the moving string as a primary and the pickup coils as secondaries, and in both cases a higher reluctance means a poorer "coupling coefficient" or "K", where K=1 means the coupling is perfect. Since a guitar pickup and string have mostly air around them, K would be much closer to zero than one. Since a transformer is not mechanical, K is a fixed value, but in a pickup, K changes a little as the guitar string moves, the change of K implies that the associated flux pattern is changing also, everywhere in space, and the coils are positioned in a place where they can see the greatest amount of whatever change is occurring, and music is made. But because a transformer is static and more ideal, it's easier to calculate what should happen, as compared with a pickup, where everything is non ideal compared to a transformer.
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asher
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Post by asher on Feb 15, 2023 16:08:04 GMT -5
If we think that the magnet is only there to magnetize the string (and can be removed), why do we think that different magnet types matter?
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Post by ms on Feb 15, 2023 17:33:09 GMT -5
If we think that the magnet is only there to magnetize the string (and can be removed), why do we think that different magnet types matter? The permanent magnet can be moved to a different place, giving information about the string magnetization. I do not think anybody said it could be removed, as in taken away altogether. Magnets can be permeable and conductive, and thus contribute to the properties of the pickup electrical circuit as well. And of course in their role in magnetizing the string magnets of different strengths affect the vibration of the string in different ways. Do you now agree with our model of string magnetization?
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asher
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Post by asher on Feb 15, 2023 18:05:54 GMT -5
What do you understand to be the parameters that must remain true regarding magnet position in order for the pickup to continue operating as expected?
I must have misunderstood. That at least makes more sense to me. But this means that the magnet is playing a significant role in the function of the pickup— not just magnetizing the string.
Of course.
I don't think this is true. I think any of the magnets saturate the string.
No— I'm fairly sure that it's wrong. But I'm trying to work through it bit by bit as I'm able to understand what you're trying to say.
My issue of understanding is not with basic electrical premises, it is with the formal expression of your argument. It would still be very helpful if anyone were to connect it to some concrete mathematical formulations.
I agree with most of what antigua said. I think the main issue is the assumptions being made about coupling, which I think functions differently in a flux field. I am still working through how I think the logic operates on that, which is why I haven't posted it yet.
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asher
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Post by asher on Feb 15, 2023 18:20:11 GMT -5
Does anyone have any measured voltage data from a pickup with a known number of turns and a known magnet as a result of string pluck?
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Post by antigua on Feb 15, 2023 22:53:33 GMT -5
asher, I think you asked why the string isn't strongly magnetized directly above the pole piece, in some post on the first page. Even though the magnetic field itself is strongest in the middle. The reason is because the guitar string becomes like two magnets, one magnet being on either side of the pole piece, each half with same polar face pointing away from the pickup, both N or both S. Therefore, in a guitar string, you have N and N or S and S facing each other right in the middle, and that creates a null in the center, where the magnetism cancels out.
The same thing happens with the six screws in a PAF, the screws are long and stick out the bottom of the pickup. Inside the pickup housing, the screws intersect with the bar magnet at about the half the length of the screw, the screw magnetizes in two directions so it will read south on the top of the screw, and south the bottom of the screw, and the two north ends are right in the middle, creating a null right there in the middle. The interesting thing about that is that if you cut off the bottom of the screws, the pole pieces will have stronger magnetism at the tops of the pole pieces, since the bottom half of the screw counteracts the magnetism of the top half of the screw.
In magnetic modeling, they talk about "guiding the path of flux" and such, but that's not really how magnetism works, magnetism is just vector math, and "flux" is the sum of all the vectors in and around whatever is being studied. Sometimes when things get confusing, I think it's easier to just remember that it's vector addition in air and in permeable material.
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Post by antigua on Feb 15, 2023 23:00:00 GMT -5
Does anyone have any measured voltage data from a pickup with a known number of turns and a known magnet as a result of string pluck? The voltage output from a string pluck varies widely based on lots of factors. The transient voltage is usually much stronger than all that comes after, and the transient will vary a lot based on how hard the string is plucked. There's lots of other variables besides. This web page claims to have some experimental data if you're looking for a ball park sound-au.com/articles/guitar-voltage.htm
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asher
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Post by asher on Feb 16, 2023 0:42:03 GMT -5
I found that as well, but I have no information about the construction of the pickup. What do we know about average magnetization of strat pole pieces? This page suggests 12700, which seems very wrong; the numbers provided at a distance seem to correspond to somewhere around 3000 gauss, which also seems high (but maybe they have to be that high since they are so small?). I just want some known data to see if I can reproduce it within a reasonable range based on math. You are suggesting that the string is magnetized latitudinally? Everything I have seen suggests that it is longitudinal. I believe I read about 3cm, but I was having trouble digging back up where I read in order to verify. The description was that the field moved along the string with poles at either end of the magnetized portion. I am not entirely clear how poles form when a permeable material is magnetized. We do know, however, that the magnetized material will participate in the same MMF vector, so I don't understand your description. Are you saying that the MMF enters the string at the center of the pole piece and then moves outward until it returns (now opposite polarity)? This would make sense to me, and was my intuitive model, but I didn't have concrete basis for it. >> As I think more about it, this description of string magnetization has to be the case. We can imagine the field lines emerging from the pole and blooming outward; they would arc onto the string in either direction, travel beyond (and along) the string until the arc declines back across the string. Why would this result in the string MMF adding to zero at the center? Does the point where pickup distortion occurs = the point where the outside string poles become substantially overpowered by the center string pole?
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Post by aquin43 on Feb 16, 2023 5:57:02 GMT -5
ms has already suggested that you read his thread link to thread, where you will see examples of the string magnetisation. There you will see that the magnetisation is zero over the pole because it changes sign there. It is also a good idea to read all of the chapters about pickups in Zollner's book which is free on line at link to book
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Post by ms on Feb 16, 2023 6:10:13 GMT -5
That table on AK's web page suggests that you have about 1000 gauss 1 mm from the pole piece of a strat pickup. When I put the probe against the pole piece from some random strat pickup, I get just under 1000 Gauss on the end pole pieces and a couple hundred less on the others. Why are you wasting people's time with stupid questions like this when it is so easy to get a meter and see for yourself? If you do not understand the theory, a little hands on experience helps.
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asher
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Post by asher on Feb 16, 2023 9:12:13 GMT -5
Maybe because I don't have a Strat? No reason to be a dick.
Why don't you try answering some of the basic questions instead of calling them stupid?
Seems more likely you don't know the answers.
If you want to be a dick, you are the one failing to ground anything in any formal math.
That you continue to refuse to do so suggests to me that you are not familiar with it, which calls into question everything you are suggesting.
I have been politely working through the claims and attempting to provide my own insight such that we may reach some greater understanding. I thought that was the goal here.
Have done so. Even if I accept the results without question, they require an explanation regarding what is going on. And I'm not convinced the test setup used there is representative.
Again, no one has connected anything to the math. You are the ones neglecting to do this, not me.
I appreciate it. I had only seen one of the chapters. I will read through the rest.
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Post by newey on Feb 16, 2023 10:32:51 GMT -5
ms, asher- Gentlepersons: This thread is rapidly descending into name-calling and ad hominem attacks. Discussions on this Forum will be kept civil, there is no basis or reason for calling other members "dicks". If you believe another member has been inappropriate towards you, the solution is to let a staff member know, rather than to engage in a "tit for tat" exchange of personal insults. "They started it" is no defense; just don't engage and continue the nastiness. You have both been warned. Further offenses may result in further staff actions, which can lead to a "time out" or an outright ban for egregious cases. As our former staff member D2o would have said: "Don't make me come down here again!"
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Post by antigua on Feb 16, 2023 10:46:30 GMT -5
asher, it's going to make a person upset if you say that your not understanding of what they are saying, and/or the fact that they can't state what they're saying with pure maths, must mean they're wrong. We're not Einsteins obviosuly, but Einstein wasn't big on math either, because at the end of the day, math has to be made to conform to the world around us, not the other way around. But if you like math you're going to love this drive.google.com/file/d/1EkaP9gMzT-MvFHL8E9Ox6KjHjS8NHD3C/view?usp=sharing I'm a hands on type myself, I have a bad habit of getting stuck in a way of thinking and I have to see directly contradictory evidence in order to get me out of that rut. I recommend this magnetometer in particular www.amazon.com/Homend-Gaussmeter-Surface-Magnetic-Function/dp/B07CNRWDJZ/ , it would make the gauss question clear instantly, as well as polar orientation. You can get a vintage style Strat pickup for just $15 www.amazon.com/SSA-12-Vintage-Staggered-Alnico-Electric/dp/B0B3QH4F9H/ For testing things out related to inductance and capacitance, this meter is really great www.amazon.com/Conversion-CD-ROM-5000-Handheld-Protection/dp/B08TV2KN1T , and you can see how the inductance changes if you replace the AlNiCo with steel slugs, or just air, and this relates directly to reluctance, because lower reluctance means higher inductance. The magnetized guitar string has a null in the middle, over the pole piece, you can see how that must be true by using that WT10-A meter, a magnet and a steel screw to act as the model of a guitar string, you can see that the screw has the same polar face on the ends, which means that the magnetic vectors have to be pointing towards the center, at the center. I find that seeing things first hand helps me a lot.
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asher
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Post by asher on Feb 16, 2023 11:11:11 GMT -5
I didn't say I thought anyone was wrong. I was asked if I agreed with the theory or not and I said I thought the theory was wrong.
Agreed, but this is not a new domain. The math exists to explain what is going on, the question is which math best applies, how to apply it, and how to understand what its application means.
This looks exciting. Thank you.
And this is awesome. I'm trying to approach the hands-on work that is being done from the theory side.
Thank you. All very useful.
This still does not explain why that would be true. I want to be able to explain this in terms of the theory.
No such thing happened. The language was used to describe the type of behavior that is not needed. It was not name calling.
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Post by aquin43 on Feb 16, 2023 11:17:08 GMT -5
A lot depends on what is expected from the mathematics. If you want an analytical solution of the flux distribution in a real string, you will be disappointed. There is no simple algebraic solution. It has either to be measured or computed numerically. The mathematics provides an insight but the problem is too complex for simple analysis.
Zollner and ms have carried out the measurement in different ways. Zollner has used a finite element analysis to calculate the flux distribution in three dimensions. I have used the results to create an approximate model of the string. Nobody here seems to have access to a full 3D magnetic modeller.
If you read Zollner's book, you will find measurements of the absolute sensitivity of a Strat pickup and even an approximate equation for the variation in sensitivity with distance from the pickup. It is this variation with distance that makes the pickup non-linear. I think that elsewhere on this forum I have modeled the expected distortion, using Zollner's sensitivity equation.
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Post by ms on Feb 16, 2023 11:31:42 GMT -5
Apparently you still have not realized the columns on the left of AK's table are properties of the material, not of specific magnets made from the material. Br (residual induction) is 12700 G for Alnico 5. What reason do you have for thinking it is too high? Well, none, you thought it was a measurement of a magnet, not a property of the material, only indirectly related to a measurement on a specific magnet. You want the math? Not going to work if you are unwilling even to look up the meaning of a column heading and try to understand how that fits into an understanding of a mathematical description of magnetic material properties.
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Post by ms on Feb 16, 2023 11:46:05 GMT -5
==> This still does not explain why that would be true. I want to be able to explain this in terms of the theory.
The basic idea of a permeable material is that the atomic dipoles, or at least larger regions made up of such dipoles, have a tendency to line up with an applied field. But this is a self consistent problem: the field that affects a given region is the applied field and the field generated by the aligment of neighboring regions. This can happen much more easily in a direction through the material that is long rather than short (more regions to affect other regions). So magnetization is much stronger along the string than across it. The applied field from the pole along the string has opposite directions on opposite sides of the pole. Therefore the magnetization must be opposite on the two sides. Thus this longitudinal magnetization must pass through zero over the pole. Exact solution must be numerical, and measurements are not trivial.
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Post by antigua on Feb 16, 2023 12:15:12 GMT -5
That's what I was going to say too, but I'll add my own wording... the reason the magnetic field in the string is not an exact refection of the magnetic field as it would be in the air is because once the string is magnetized, each atom or magnetic domain in the string forms its own magnetic field, which effects the immediate neighboring atoms in the steel, causing a chain reaction. The higher the permeability, the stronger the chain reaction will be, because what permeability is, is a description of how willing magnetic domains are to being re-oreinted by an ambient magnetic fields, where ambient magnetic fields are both external field as well as the fields of their immediate neighbors in the material itself. I suspect the math is complicated because of that chain reaction, which is why when you model a magnetic model with FEMM software www.femm.info/wiki/HomePage , it takes a while for it to process, it has to do a ton of processing work to create a graphical depiction of the flux path, and in only two dimensions, let alone three.
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asher
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Post by asher on Feb 16, 2023 12:35:27 GMT -5
Again, no need for the attitude.
I made no such assumptions. I took the measurement for Br and applied it to the formula for calculating field force at a distance from the center of the pole of a cylinder magnet:B(x) = {\frac {B\scriptstyle{ r }} 2} [ {\frac {L+X}{\sqrt{ R^2 + (L+X)^2}} } - { \frac x {\sqrt{ R^2 + x^2}} } ]
Seems I made a typo with X and x. Doesn't seem I can edit.
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Post by ms on Feb 16, 2023 13:27:27 GMT -5
Again, no need for the attitude. I made no such assumptions. I took the measurement for Br and applied it to the formula for calculating field force at a distance from the center of the pole of a cylinder magnet: B(x) = {\frac {B\scriptstyle{ r }} 2} [ {\frac {L+X}{\sqrt{ R^2 + (L+X)^2}} } - { \frac x {\sqrt{ R^2 + x^2}} } ]
Seems I made a typo with X and x. Doesn't seem I can edit. This is all you wrote: ==>What do we know about average magnetization of strat pole pieces? This page suggests 12700, which seems very wrong; I think is right if the units are Gauss.
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asher
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Post by asher on Feb 16, 2023 13:30:29 GMT -5
I apologize for any offense that I have given. My expression of skepticism was not intended as disrespect or to diminish the value of the work that each of you has done.
I am attempting to engage here in order to elucidate the finer details of what is going on in a way that can be related to the existing and well-known mathematical formalisms regarding the domain. I have not yet seen this done, but I think that the knowledge here can be a big part of making it possible.
I appreciate that you have each continued to engage me. I ask only that you treat my skepticism and seemingly basic questions with respect, as we are in pursuit of the same thing.
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asher
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Post by asher on Feb 16, 2023 13:41:44 GMT -5
The distances are given in mm, so I converted to Tesla and m then the result back to Gauss.
If I set Br as 3000 I get exactly the table numbers.
How are you handling mm if you use Gauss?
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Post by antigua on Feb 16, 2023 13:48:22 GMT -5
The distances are given in mm, so I converted to Tesla and m then the result back to Gauss. If I set Br as 3000 I get exactly the table numbers. How are you handling mm if you use Gauss? If you mess around with the WT10-A you find that the Gauss varies a lot depending on where the probe is placed. That table implies that the probe is 1mm above the center of a pole piece. Usually AlNiCo is sized to be about four times longer than it is wide, because it achieves the highest Br with that geometry, so even though they don't describe the conditions that led to the Gauss value, their numbers are consistent with what the WT10-A will show. The WT10-A give milliteslas, you convert that to Gauss by just multiplying mT by 10. Why the math doesn't work out, I have no idea, but the math will be wrong sooner than reality will be wrong.
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Post by ms on Feb 16, 2023 13:52:00 GMT -5
The distances are given in mm, so I converted to Tesla and m then the result back to Gauss. If I set Br as 3000 I get exactly the table numbers. How are you handling mm if you use Gauss? All I did was check another source for Br of Alnico5. It gave the same number (12700 G) after converting from mT. That is why I think AK is right. Maybe both the other source and AK are wrong, but in any case, the field strength of strat pole pieces is well known, and there is no need to compute from Br. Edit: A couple more things: 1. The equation consists of Br times a unites factor. You have distance/distance, and so distance units do not matter, but all must be the same. 2. I believe this equation is for uniform magnetization. Alnico has sufficient permeability so that this is not completely correct, and you need a self-consistent solution. Exact agreement might be accidental.
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asher
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Post by asher on Feb 17, 2023 12:44:43 GMT -5
The field of a permanent magnet is not a function of the material's permeability. Permeability is a term relating to applied magnetic fields.
If the math isn't within the same order of magnitude, the assumptions are wrong.
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Post by ms on Feb 17, 2023 13:24:19 GMT -5
The field of a permanent magnet is not a function of the material's permeability. Permeability is a term relating to applied magnetic fields. Each region in a magnet makes a field and and is potentially influenced by the fields of all other regions, the same nasty "self-consistent" problem you often have. If the material is not permeable, such as almost holds true for neodymium, then there is no significant effect. Alnico is permeable, and so the effects of "applied magnetic fields" from region to region must be accounted for.
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asher
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Post by asher on Feb 17, 2023 16:45:59 GMT -5
According to your reluctance theory, what would you understand to change if we replaced the permanent magnet with a HyMu-core solenoid at equivalent field strength (relative permeability at this H is about 250,000)?
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asher
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Post by asher on Feb 17, 2023 17:11:46 GMT -5
At the very least, I have confirmed that the equations do not work for Alnico, apparently because it is not linearly organized. That seems like it would line up with your explanation.
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