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Post by ms on Mar 4, 2024 14:34:29 GMT -5
Section 9 on shielding (and also on hum bucking, although this is not in the title) contains many errors. They follow from the misconception that both shielding and humbucking reduce hum from "electromagnetic fields". Shielding reduces hum from electric fields, while humbucking reduces hum from magnetic fields. A propagating electromagnetic wave (radio, tv, cell phones, etc.) has both kinds that oscillate together. This is not usually a problem for guitars because the frequency is so high and guitars do not efficiently "detect" the modulation on the wave.
Section 11 on single coil versus humbucking says that the major difference in sound is a result of harmonic canceling from sampling one versus two regions on the string. This is a real effect but minor, and only affects the lower frequency strings. The relevant harmonics are high number and out of the bandwidth of the system on the higher frequency strings. Humbuckers sound darker because they have higher inductance. Well, not all single coils have lower inductance; for example, a P-90 has high inductance. The myth is that a P-90 has good high frequencies because it is a single coil pickup, but it does not.
Also, stacked hum buckers do not have cancelled bass. There is some loss in output level from coupling between the coils at all frequencies.
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Post by ms on Mar 4, 2024 13:12:17 GMT -5
Go to Kinman's webpage and look up his description of this pickup. You find this: "The sounds range continuously variable from the focused growl of a P-90 with stellar highs..."
Yes, most people believe that a P-90 has "stellar highs", but this is not correct. A P-90 has typically 10,000 turns and steel screws with a relatively flat bobbin, and so the inductance is more than 6 H. That is, not many highs at all. (Yes, you can reduce the number of turns to about 8500 to 8600 and get the inductance down to about 4.5 H, and it sounds similar to a PAF humbucker, still not "stellar highs". So Kinman is playing up to a commonly believed myth, casting doubt on his description. Perhaps the only way to find out what this pickup does is to get one.
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Post by ms on Mar 4, 2024 12:52:20 GMT -5
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Post by ms on Feb 27, 2024 6:21:18 GMT -5
Suppose that you have a 10,000 turn single coil pickup, using steel cores or blade. Now make a pickup with two 5,000 turn coils in series. An important difference is that the output levels could be similar, but the inductance of the two coil pickup would be lower. This is because output level varies roughly with the number of turns while the inductance can vary as quickly as the square of the number of turns. If so, the inductance of each of the two coils is one quarter of that of the single coil, and the series combination is one half. Now try four coils. Output level should stay about the same, but the inductance should drop further. So it seems to me that a quad rail pickup is a way of keeping the output level high and lowering the inductance.
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Post by ms on Feb 16, 2024 6:28:08 GMT -5
I do have a question regarding the first post in the thread. What's an "exciter" and how does it work? I saw one on a vid on YouTube and I asked that guy but I don't think he replied. Whats it for? I assume it's used to "excite" the pickup being tested? So it's used to induce the voltage into the pickup, essentially replacing guitar strings and strumming/plucking a note? Is that close? It's a coil, with or without a magnetic core, a ferromagnetic permeable material. A permanent field is not needed. An audio current passing through the coil wire causes a time varying magnetic field. When placed so that the field passes through the pickup coil, the voltage induced in the pickup can be used to characterize its performance. The pickup has inductance, resistance and capacitance, and so the analysis yields information about these components. It also gives information about losses caused by currents in metal parts. These currents affect the electrical component values and also can reduce the output of the pickup by canceling part of the exciting field. If instead you apply a voltage to the pickup terminals and measure the current through it, you get the impedance as a function of frequency, which is also a measure of the electrical components. Both kinds of measurements are necessary for a complete characterization of the pickup, but such a complete measurement could be more than you need.
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Post by ms on Feb 12, 2024 17:01:37 GMT -5
Looks like the Duncan Stag Mag is not the only humbucker design with magnetic poles. The Rio Grande Tallboy and Muy Grande are a very similar approach, and the Fralin Twangmaster is also along the same lines but different. and the rio grande halfbreed. Those are expensive pickups. The Fralin twangmaster is something else. Not sure what, but it looks like it gets hum canceling with two coils, each containing three of the pole pieces. The coils are separated (in the direction along the strings) to prevent field cancelation I guess, but at the expense of continuity in location. I think.
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Post by ms on Feb 12, 2024 13:44:29 GMT -5
Yea, that stagger is definitely a head-scratcher. I've also seen a number of anecdotes that it's a better neck pickup than bridge pickup. The design and idea is interesting. I feel like the best use of this something like this is combined with a relatively hot conventional bridge humbucker for good versions of the following four tones: *Strat neck solo (Stag Mag neck outer coil) *Strat notch position (Stag Mag neck inner coil + bridge humbucker inner coil) *Tele middle position (Stag Mag neck outer coil + bridge humbucker outer coil) *Hot bridge humbucker solo In my old fashioned view, I would want to emphasize the bridge pickup. IMO, the tele bridge is the classic electric guitar sound, while the PAF bridge, not such a great tone considered alone, is a good contrast to the tele sound.
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Post by ms on Feb 12, 2024 12:38:37 GMT -5
I'm still impressed that it can BS as well as it does. Is it really worse than the BS pickup makers put out? A lot of the mistakes become apparent only after you connect the dots, like the distinction between whether voltage causes current or current causes voltage. A lot of times Chat GPT has the ability to come up with the right answer after you inform it of it's mistake. There has also been talk about Chat GPT being "lazy", and this does seem like laziness. I don't understand how the algorithms work, but I wonder if the mistakes are due to a lack of self-checking. Like when it makes up facts, why can't one Chat GPT take the answer of another Chat GPT, and interrogate it's answer before it presents to the end user? Hopefully at some point it will see Manfred Zollner's work, and we can prompt "according to Zollner..." I really like "according to Zollner...". I think of prompting with this as a way to get it to go looking in Zollner's book. Not sure if it will delve into translated PDF files. The translations are excellent, but it still might find some way to get confused. I need to think of the right "hook" to introduce this.
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Post by ms on Feb 12, 2024 12:27:17 GMT -5
That's basically the design of the Seymour Duncan Stag Mag, right? I haven't looked into it much, maybe I should. antigua regardless of PRS's marketing (much of which does seem like bunk) their results are interesting in the TCI and TCI "S" pickups. Going by the data in the Guitar Pickup Database and DCR measurements by Phillip McKnight, it seems the basic design is an asymmetric wind with the slug coils about twice as strong as the screw coil, A5 magnets, relatively high inductance for the DCR (5.85H, 8.84 Ohms), and a 2.8Khz resonant peak that seems intentionally pegged right between a PAF and Fender single coils (like with a lot of PRS approaches trying to find the center between Gibson and Fender). Interestingly they apparently don't use a ground wire, which may be to keep less pickup hardware out of the circuit? And from photos of the USA version TCI I think the baseplates may even be plastic. For the non-US TCI "S" it looks like earlier versions used a nickel-silver baseplate and later revised to brass. Well I had not heard of that. A couple of comments: Why traditional stagger? Do they really want your plain G string to be too loud? They seem to imply that you keep your 500K pots since they recommend a Pearly Gates in the neck position. They also claim it is high output. I think they are running a delicate balancing act by using smaller than #42 wire to increase the damping to compensate for the 500K pots in the sc mode, as well as allowing more turns to keep the sc output level high. I suppose this limits the range of possible hb characteristics, but it could be what you want, right? What I am thinking of would have a different range of possibilities.
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Post by ms on Feb 12, 2024 11:47:36 GMT -5
Would that be to start off with a relatively high-Q humbucker, split it to single (which would raise the Q further?), then add capacitors to bring Q down to the desired level? Capacitance would bring down the resonant frequency and that is certainly an important tool. But, yes, starting with a higher Q humbucker is it, and the way I see to do that is to make it from two Fender type sc coils (Alnico cores rather than slugs or screws), not a new idea, but maybe not fully explored for this purpose. Use 250K pots and you nail the split coil single coil sound. Put the two coils in series with the 250K pot and you are moving in the right direction because you are starting with higher Q coils that might need to be lowered (as the loss induced by the 250K would do) when used as a humbucker. I would make the two coils in one pickup the same for good hum cancelation, and lower the resonant frequency as necessary by switching in parallel capacitors (and resistors if necessary). The switching here could get a bit complicated. Something to think about.
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Post by ms on Feb 12, 2024 11:28:44 GMT -5
Cool! Feels good to be learning stuff Now I feel like I better understand the focus that PRS has taken around increasing inductance with moderate resistance. That helps get that higher-output higher-clarity humbucking tone they're aiming for while simultaneously creating an inherently better-splitting pickup. Would it be reasonable to say that this approach also helps mitigate the (split-coil) difference between steel poles and magnetic poles? Yes, although it is not easy to achieve everything. For example, it is easier to increase loss (lower Q) than decrease it (raise Q), but decreasing loss might be what you need to do. It occurs to me that there is another possible approach to coil splitting humbuckers that would start with higher Q (lower loss). Can you see what I am thinking of?
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Post by ms on Feb 12, 2024 10:30:25 GMT -5
Another observation based on the limited data I'm looking at and limited understanding: I'm finding that models that achieve a higher inductance comparative to their DCR (H/Ohms) also correlate with slightly higher resonant peaks. Would it be reasonable to say that, other things being equal, those designs that achieve a given inductance with lower resistance will generally have higher resonant peaks? Exactly. The concept of Q was invented to cover this. The Q of a coil is 2*pi*f*L/R. It is a bit complicated since in addition to loss from winding R, there is loss from eddy currents. Often the loss from winding R is dominant, and so your measurements are right on.
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Post by ms on Feb 12, 2024 10:01:47 GMT -5
"User You are correct that the flux density from the pickup magnet reaches its maximum density over the pole piece, but since the magnetization reverses direction over the pole piece, the magnetization is not maximum there but rather goes through zero. It does, however, reach a maximum near the edges of the pole piece or just outside of it.
ChatGPT You're absolutely correct, and I appreciate the clarification. I apologize for any confusion. The magnetization induced in the guitar string does indeed reach its maximum near the edges of the pole piece or just outside of it, rather than directly over the pole piece where it reverses direction.
This phenomenon occurs because the magnetic flux density is highest directly over the pole piece, but the magnetization induced in the string itself goes through zero at that point due to the reversal of direction. Near the edges of the pole piece, where the magnetic field is still strong but the direction is consistent, the induced magnetization reaches its maximum.
This spatial pattern of magnetization, with its reversal over the pole piece and maximum near its edges, is crucial for the pickup's functionality and contributes significantly to the unique tone and response characteristics of different pickup designs. Thank you for the clarification."
So this is just complete BS in this sense: It is assuming I am correct, and trying to agree in an intelligent seeming way. Kind of disappointing. It does not appear that chatGPT understands guitar pickups at all. It is all verbal smoke and mirrors.
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Post by ms on Feb 12, 2024 9:53:35 GMT -5
"User The induction of magnetization in the string by the pickup magnet has an important spacial pattern, in particular a reversal of direction over the pole piece. Why have you not discussed this?
ChatGPT You're correct; I didn't address the spatial pattern of magnetization induced in the string by the pickup magnet, particularly regarding the reversal of direction over the pole piece. Let's delve into that further:
In a typical guitar pickup design, there are one or more pole pieces placed beneath the strings. These pole pieces are regions of concentrated magnetic flux produced by the pickup magnet. When a guitar string vibrates above these pole pieces, it interacts with the magnetic field in a spatially varying manner.
At the pole piece, where the magnetic flux density is highest, the magnetization induced in the guitar string reaches its maximum intensity. As the string moves away from the pole piece, the strength of the induced magnetization decreases. Importantly, when the string crosses over the pole piece, the direction of the induced magnetization reverses.
This reversal of magnetization direction is due to the changing orientation of the magnetic field as the string moves across the pole piece. It's a crucial aspect of how the pickup senses the vibration of the string. The changing magnetic field induces alternating current in the pickup coil, which corresponds to the vibration pattern of the string. This alternating current is then amplified to produce sound.
The spatial pattern of magnetization induced in the string, including the reversal of direction over the pole piece, contributes to the unique tonal characteristics of different pickup designs. For example, pickups with staggered pole pieces may provide a more balanced response across the strings, while pickups with flat pole pieces might emphasize certain frequencies."
This seems more like BS rather than understanding.
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Post by ms on Feb 12, 2024 9:47:40 GMT -5
"User Faraday's law says voltage is induced. Why do you say current?
ChatGPT You're correct; I misspoke. Faraday's law states that a changing magnetic field induces a voltage, not a current, in a coil of wire. This induced voltage, in turn, causes an electric current to flow in the circuit if there is a closed loop.
So, to clarify, when a guitar string vibrates above a pickup magnet, it induces a changing magnetic field, which in turn induces a voltage in the coil of wire wrapped around the pickup magnet. This induced voltage drives an electric current in the circuit connected to the pickup, which is then amplified and converted into sound. Thank you for pointing out the error."
So it can be corrected. I wonder if it will remember this correction.
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Post by ms on Feb 12, 2024 6:59:07 GMT -5
I think it's time for me to learn more about this stuff. I finally went over one of your analysis, of the Epiphone 57CH pickup, and it's all extremely interesting. I've never looked into pickups this much, even after all the stuff youve posted at ST since I've been there. But I think it's time to start learning. Now that I've started buying better pickups, I've become a lot more interested in all of it. I know you've tested Seth Lovers and 59s so I'll have to find your analyses and see what I can learn! Edit: apparently your analyses are quite popular. If you type "Antigua pickup" into Google, it finishes it with "...analysis". That's saying a lot! Nice job! That's funny. I often use Google to look up my old info. That's one of the reasons I post it on the internet. This article about how pickups work is pretty good www.buildyourguitar.com/resources/lemme/ , also Manfred Zollner's work is great gitec-forum-eng.de/wp-content/uploads/2020/09/poteg-5-magnetic-pickups-a.pdf At some point AI will ingest Manfred Zollner's work and AI will understand how pickups work better than any human. User What are the details of the magnetization induced in a guitar string by a pickup magnet? ChatGPT: "When a guitar string vibrates above a pickup magnet, it induces a changing magnetic field according to Faraday's law of electromagnetic induction. This changing magnetic field induces an electric current in the coil of wire wrapped around the pickup magnet. The induced current carries information about the vibration of the string and is then amplified and sent to the amplifier, producing sound. The details of the magnetization induced in the guitar string by the pickup magnet depend on several factors: Magnetic Field Strength: The strength of the magnetic field generated by the pickup magnet influences the amount of magnetization induced in the guitar string. Stronger magnets can induce stronger currents in the coil. Distance from the String: The proximity of the pickup magnet to the guitar string affects the strength of the induced magnetic field. Closer proximity typically results in stronger induction. Material and Gauge of the String: Different materials and thicknesses of guitar strings will have varying responses to the magnetic field. For instance, steel strings are more responsive to magnetic fields than nylon strings due to their ferromagnetic properties. String Motion: The movement of the guitar string itself affects the changing magnetic field. As the string vibrates, the magnetic field it interacts with changes accordingly, inducing varying levels of magnetization in the string. Coil Design and Number of Turns: The design of the coil wrapped around the pickup magnet, as well as the number of turns of wire, can affect the sensitivity and response of the pickup to the induced magnetic field. Overall, the process involves the interaction between the vibrating guitar string and the magnetic field generated by the pickup magnet, resulting in the induction of an electric current in the pickup coil, which is then amplified and converted into sound." Let's check the progress in understanding. First, it is a voltage that is induced, not a current. The current flows because the electrical elements of the circuit are excited by a voltage. This program loves to propagate errors; it has not yet learned how to distinguish repetition of incorrect answers from proper understanding? Why? It could look up Faraday's law and fix this error, even if it is still decades away from actually understanding physics. The rest of the answer is very shallow. It does not understand that the field inside the string has a spatial pattern that is important to understanding. It must have ingested some of Zollner's work (and several others'). but it selects the shallow discussions, apparently because it weights frequent repetition over careful logical analysis. I do not understand why; it should be able to detect material that contains logical deductions as well as facts (or statements that appear to be facts). Apparently it is mainly just a language analyzer.
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Post by ms on Jan 30, 2024 18:19:38 GMT -5
I think taking out the 6 db per octave slope gives the correct value of the resonance. What you need is a flat test signal to get the right answer for the values of the electrical components.
I also think that the correct inductance is what you measure at low frequencies, say 100 Hz, below the frequency range where eddy currents matter much. Then it is consistent with the math to look at the shift in resonant frequency from the "simple" value as a result of additional components in the circuit, which have a significant effect in the few KHz range..
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Post by ms on Jan 30, 2024 13:55:02 GMT -5
I took ferrite core off my probe and constructed jig 470pF cap paralell with 470kOhm resistor connected with 5cm cable to 1/4 jack. Jack goes to Boss Metal Zone as a buffer and then to my audio interface. I guess Metal Zone should have 1Mohm load. Swamping resistor was 47nF connected when used. My probe transformer has 5ohm winding with central tap and second winding of 0.3ohm. I use only 5ohm winding. It looks almost the same as Ken Willmott presents. Then I measured my reference 57/62 strat pickup, some other strat pickups as well as three humbuckers. Here are the results: Pickup | DCR (kohm) | f res @470pf (kHz) | f res @47.5nF (Hz) | calculated* L (H) | Fender 57/62 | 5.9 | 4.1 | 500 | 2.2 | Pearly Gates Bridge | 8.2 | 3.4 | 340 | 4.6 | Gibson BurstBucker2 | 8.3 | 3.1 | 340 | 4.6 | SD SJBJ | 15.6 | 2.0 | 250 | 8.5 |
* I used simplified f res formula with 1/sqrtLC Conclusion: If Antigua measued pickup values are correct, my implementation of Ken Willmott method in case of measuring humbuckers are giving false results while delivering excellent results with single coils. In situ or not does not matter. 1/sqrtLC is more accurate for Fender single coils because they use Alnico magnet cores, which have lower eddy currents than the steel used in humbuckers . I suppose that if you wanted verify if this is a factor in your measurements you might measure a P-90, single coil but steel cores, or one of those cheap strat pickups with steel cores. Why do you need the Boss pedal? You should have plenty of gain with the instrument input of your audio interface. Yes the metal zone is 1 M input impedance according to a schematic I found somewhere. But does it have flat enough frequency response? The circuit is complicated, and I did not figure it all out.
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Post by ms on Jan 30, 2024 12:39:43 GMT -5
"I was just lucky to find a small transformer that does a job."
What kind of transformer is this? Transformers are usually designed to keep flux in their own local magnetic circuit. An exciter coil is designed to send flux through the pickup coil. All transformers have some leakage flux that escapes the local circuit, but it might not be much, and I suppose that it is possible it could affect your frequency response.
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Post by ms on Jan 30, 2024 9:46:19 GMT -5
"...ferrite core which permability is lower than air is an issue"
Air is about the same as vacuum and you cannot go any lower than that. Ferrite can have a permeability from somewhat greater than vacuum to many thousand times greater. In general, ferrite permanent magnets have low permeability, and the many types that do not have significant permanent magnetism vary widely. I prefer to use a very small air core exciter that can illuminate a single pole piece as the string does. (You need good SNR in the measurement setup.)
For in situ, if you do not like Antigua's method, a short Low C cable can be not too much worse. The idea is to keep good sensitivity at high frequencies, although this is not as much of a problem as it might seem since the law of magnetic induction depends on the time rate-of-change of the signal.
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Post by ms on Jan 29, 2024 11:38:24 GMT -5
You really need both exciter coil measurements and measurements of impedance versus frequency. Then you need to assemble all that information into a coherent model, and then you can predict what you should measure in a specific set of conditions.
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Post by ms on Jan 10, 2024 5:47:23 GMT -5
But you cannot do that with a single EQ circuit. The location of a pickup determines the relative intensities of the string harmonics. But the actual frequencies are different for each string (because the harmonics are the same). Therefore each string would have to have its own pickup and equalizer. Technically this is true, we're talking about a difference in harmonic timbre versus amplitude by frequency, but I think if you cut out a portion of the frequency out, you get a result that is sonically similar to the altered timbre, I think because the neck pickup timbre is defined by particular harmonics being greatly reduced, and with the EQ you are taking away amplitude that roughly overlaps with the missing harmonics of the neck pickup. The reason I'm as confident about this as I am is because I made my own Veritone control, and chose my own cap values, and notices some cap values did make the bridge seem a lot closer in sound the the neck or middle pickup, depending on the value of the cap. The bridge pickup has relatively even harmonic amplitudes compared to the neck and the middle, so it can serve as a good base signal to be reduced into other timbres. With active EQ, the RLC filtering would be a lot more robust than what a Veritone control can do. Yes, for example, a general property of sensing at the bridge pickup position is that the fundamental and lower harmonics are relatively reduced in level. So if you EQ to raise the bass on a bridge pickup signal, it will sound more like a neck. On the other hand, a specific property of the sound of a neck pickup with an open string is that the fourth harmonic has greatly reduced strength relative to other harmonics. The frequency of this varies so much from string to string that you cannot do a good job of simulating this with EQ from a bridge pickup signal. EQ is good for making one pickup sound like another in the same position, but not as good for different positions.
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Post by ms on Jan 9, 2024 16:08:51 GMT -5
Here, incidentally, is an example of a guitar equipped with an active EQ circuit intended to simulate a neck pickup. But you cannot do that with a single EQ circuit. The location of a pickup determines the relative intensities of the string harmonics. But the actual frequencies are different for each string (because the harmonics are the same). Therefore each string would have to have its own pickup and equalizer.
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Post by ms on Jan 1, 2024 16:31:21 GMT -5
"But the recordings sound great..."
I agree. This is a very good test.
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Post by ms on Jan 1, 2024 7:03:32 GMT -5
Here's the plots as before this time covering the range 1000 to 5000 Hz: Not sure what can be deduced there! But, if we're looking at pickups with L in the range 4.2H to 5.4H, with capacitance of 214pF (cable) plus allow 100pF (windings) plus allow 100pF (amp input and general guitar wiring), then we are looking for treble resonance in the 'ball park' range 3400Hz to 3800Hz. This is quite a bit higher than usual for humbuckers in this inductance range. I am wondering if preferences might be different with a higher capacitance cable, giving a somewhat thicker (and more common) sound.
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Post by ms on Nov 23, 2023 6:56:46 GMT -5
I would like to suggest the first part of this:
What the Pickup "Sees": Its Aperture, Manfred Zollner (https://www.gitec-forum-eng.de/wp-content/uploads/2021/04/z60e_aperture_mt.pdf).
It begins with a description of why the aperture might matter, that is, the filtering out of possibly important high frequency components, and then describes an aperture measurement technique and shows the results, which can be summarized in a simple way as "in a Fender type single coil pickup, it is the diameter of the magnet that approximately defines the aperture." (This should apply in an approximate way to the steel slug or screw in a Humbuckers or P90. There is a confusing translator's note near the end of the paper which casts doubt on this, but I do not think that this note is correct.)
After the description of the measurement, the paper becomes more complicated, developing a model describing the results. This requires some physics knowledge, and I do not suggest studying it unless you have some such knowledge and a strong desire to understand how this works.
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Post by ms on Nov 22, 2023 13:12:12 GMT -5
timtam asked me to comment also on the McD explanation that is first on the list places to go first in a previous post. Near the end of Section 1 there is a figure, the last figure in that section. It shows a permanent field pointing perpendicular to the string and away from the coil. This field is uniform; that is it does not vary in space as well as time. It produces string magnetization in the same direction as it points. The resulting field from this magnetization points through the coil and so produces a voltage when the string vibrates, changing the flux density through the coil. As I described earlier in the thread when describing Tillman's explanation, the field through the coil actually results from magnetization pointing along the string. This magnetization is zero right over the pole piece and points in opposite direction on opposite sides of it. It is this change that causes the component of field through the coil. McD did say that his model is simplified, but it is easy to miss what that means.
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Post by ms on Nov 21, 2023 6:08:38 GMT -5
That's a great explanation ms, thanks for that. Do you have any field diagrams, links to diagrams or (even more fabulous) links to software than can generate diagrams for any given geometry? Kit aquin43's threads and posts in other threads are a great place to look. For example: guitarnuts2.proboards.com/thread/8530/2d-magnetised-string-simulation
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Post by ms on Nov 20, 2023 12:51:58 GMT -5
Maybe ms you could elaborate on how that section of Tillman would be improved ? And where McDonald is maybe not correct. I also recall someone questioning some of Jungmann recently. All that is kind of what a Journal Club does - pick a paper, summarize its important bits, and then dissect it.
Sure, happy to. The problem with Tillman's analysis in the section "Effects of pickup width" is that the the aperture is determined by the width of the pole piece, not the pickup. To understand this we need to consider the answers to two questions: 1. What is the purpose of magnetizing the string?, and 2. What is the nature of this induced magnetization? The purpose is to produce magnetic flux pointing along the axis of the coil, that is perpendicular to the plane of the windings and through the coil. The magnetization flux must vary when the position of the string changes. Long thin objects, such as guitar strings, magnetize along their length. The important thing is that this magnetization points along the string, but in opposite directions towards the bridge and the nut as you move away from the pole piece. This is because magnetic field lines of the permanent magnet come out of the top of the pole piece and bend over, eventually reentering the pole piece at or near the other end. It is the component of this field along the string that magnetizes it, and you can see that it points in opposite directions towards the bridge and nut. Field lines leak out of the string progressively along it, and they return to and re-enter the string at or near the pole piece. (You can think of the magnetized string as two long thin magnets, one on each side of the pole and pointing in opposite directions.) This bending of the field lines (of the "string magnets") near the pole piece (so they can reenter the string) makes the component of the field from the string that points through the coil. This only happens at or near the pole piece, and so the aperture is about equal to the width of the pole piece. Also you can see the field lines from both "string magnets" have components through the coil that point in the same direction so that they add rather than cancel.
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Post by ms on Nov 20, 2023 6:19:28 GMT -5
Towards the end of of Tillman, "Response Effects of Guitar Pickup Position and Width": "Pickups do not sense the string at a single point source, but rather over an area due to the width of the magnetic field. This sensing area is called the "aperture" of the pickup and is about an inch wide on a thin single coil pickup and about 2.5 inches wide on a wider pickup such as the Gibson humbucker."
I wouldn't refer to this unless he fixes it. This is a popular article, and so responsible for much misunderstanding.
McD's article is a great introduction to how the law of magnetic induction works, but it is very much intended to be viewed with "physics thinking", that is, something made fun of by the old joke about assuming a spherical cow. His assumptions about the magnetic field from the string are not in line with reality, and he does not make this clear.
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