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Post by ms on Mar 14, 2017 8:55:29 GMT -5
This is follow up on some discussion begun here: guitarnuts2.proboards.com/thread/7905/seymour-duncan-little-analysis-review. These are not easy measurements to make, but at the very least one should be able to decide this: is the length of string sampled closer to the diameter of the pole piece, or to the width of the pickup? Analysis of the physics of the pickup says that "pole piece" is the right answer. What do measurements indicate? I will start with a very simple measurement; discussion and further measurements will be required. Start with a single coil sized pickup in the guitar. This pickup uses ferrite poles pieces about .2 inches in diameter, and each pole piece has a 3/16 inch diameter, 1/32 inch thick neo magnet on top. This is not a single coil, but rather six individual coils, but that does not matter because the measurement is made with a single coil pickup placed above the strings over the guitar pickup such that it can be slid along the strings to sample the field produced by the vibrating string magnetized by the magnet in the guitar pickup. The measurement pickup is air core for this first measurement (wound on a single core plastic bobbin). Three measurements are made by carefully plucking the string, one centered over the guitar pickup, and then slid along the strings by 3/32 and 3/16 inches. The measurements are converted to db referred to the centered measurement, and the measurements are 0 db, -3.1 db, and -18.4 db. Thus 3/32 inches is the half width measurement or 3/16 inches the full width of the sampling length at approximately the 3 db points. The fall off is very rapid after that and so this defines the effective sampling length. Thus this measurement says that the sampling length, based on sampling the magnetization of the string by the magnet in the guitar pickup is a pole piece width rather than a pickup width. I do not see any ambiguity in this conclusion, but I do see that additional refining measurements would be useful. Next I will repeat the measurement with a hum bucker in a guitar, same sampling coil, and then repeat both with a core in the sampling coil. |
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Post by antigua on Mar 14, 2017 13:11:14 GMT -5
That's an interesting approach. My plan was to sort of approximate what happens when you bend a guitar string such that it's between two pole pieces. I would mount a pickup over the string, but offset so that only one pole piece is over one moving string. I'd use an eboy to excite the string, then slide the pickup perpendicular to the string in measured increments and measure the change in dBV.
One reason I expect the drop off to not be abrupt is because performing string bends between pole pieces into the "dead space" is not all that bad. Some guitarists are bothered by it, so they use rail style pickups, but I've personally hardly ever noticed a volume drop as a result of string bending.
The other open question is whether or not compression effectively widens the reach my amplifying that content that is further away from the pole piece. I don't know enough about audio signal compression to intuit an answer.
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Post by JohnH on Mar 14, 2017 14:10:32 GMT -5
That seems very interesting and clear for the single coil. I've also though Tillman had it too wide, and so I was using coil width instead of his value greater than that. But I see it should be reduced again.
On the HB's, it would be interesting to see if the response dips significantly between poles and then how it falls off outside the poles
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Post by ms on Mar 15, 2017 7:59:54 GMT -5
That's an interesting approach. My plan was to sort of approximate what happens when you bend a guitar string such that it's between two pole pieces. I would mount a pickup over the string, but offset so that only one pole piece is over one moving string. I'd use an eboy to excite the string, then slide the pickup perpendicular to the string in measured increments and measure the change in dBV. One reason I expect the drop off to not be abrupt is because performing string bends between pole pieces into the "dead space" is not all that bad. Some guitarists are bothered by it, so they use rail style pickups, but I've personally hardly ever noticed a volume drop as a result of string bending. The other open question is whether or not compression effectively widens the reach my amplifying that content that is further away from the pole piece. I don't know enough about audio signal compression to intuit an answer. Yes , unless you are playing very clean, you will probably not notice that the gain falls off between poles since the distorted level does not fall all that much. Also remember that it takes about a 10 db drop to sound half as loud. |
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Post by ms on Mar 15, 2017 8:10:57 GMT -5
That seems very interesting and clear for the single coil. I've also though Tillman had it too wide, and so I was using coil width instead of his value greater than that. But I see it should be reduced again. On the HB's, it would be interesting to see if the response dips significantly between poles and then how it falls off outside the poles The humbucker will be different. For one thing, the pickup in this guitar currently under measurement has long pole pieces that tend to give a tight field. A humbucker has shorter pole pieces, and thus a broader pattern of magnetization. What we are looking at with this test so far is the response of a pickup coil to the string magnetization, that is, how it changes with distance along the string. That is, the sensing pickup coil is right there close to the magnetization. In actual pickup operation, the magnetization out there along the string is sensed by a pickup could that is not there, but back at the center. Thus it sees a weaker signal, and so the dbs down would increase some more. With this pickup under test, the difference might not be so great since it is already quite narrow in the magnetization, but with a humbucker, you might have to look at both effects together. It might be useful to use a driven sensing coil moved along the string to get this second factor and then take the product with the first factor. The hum bucker does have a deep drop in the middle: the field is weak and horizontal there. |
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Post by wgen on Mar 15, 2017 13:20:02 GMT -5
I was reading this thread with much interest. Just a question:
In your opinion, would the harmonics sensing be any different when lowering the pickup, let's say, with the pole pieces a couple of millimeters lower than usual?
I'm asking because I was referring to the fact that the pole pieces would read more of the full string vibration when lower, or, maybe better, more of the flux change of the vibrating string, of which Antigua talked about once.
Wouldn't it be more like having a wider sampling region than the strict 0.2 inches of width pole pieces?
Thank you very much in advance!
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Post by stratotarts on Mar 15, 2017 18:46:29 GMT -5
I would expect the window to get smaller as the distance between the string and the pole piece decreases. The field diverges as it gets further away from the pole.
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Post by wgen on Mar 15, 2017 19:22:49 GMT -5
I would expect the window to get smaller as the distance between the string and the pole piece decreases. The field diverges as it gets further away from the pole. Thank you very much! That makes sense... |
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Post by ms on Mar 15, 2017 20:55:43 GMT -5
I would expect the window to get smaller as the distance between the string and the pole piece decreases. The field diverges as it gets further away from the pole. But that is not the whole story. If you have a pole piece of diameter D, and you are looking significantly closer to it than D, I would expect the window to change slowly, but as you get further away it should change more quickly. All magnetic sources look like dipoles if you get far enough away, but up close it is different. Consider the field of a solenoid (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html). Inside the solenoid the field is uniform, but as the lines come out an end, they diverge, but right outside they are nearly straight, especially near the center of an end. (The field strength is proportional to the density of lines.) |
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Post by stratotarts on Mar 15, 2017 21:28:00 GMT -5
I would expect the window to get smaller as the distance between the string and the pole piece decreases. The field diverges as it gets further away from the pole. But that is not the whole story. If you have a pole piece of diameter D, and you are looking significantly closer to it than D, I would expect the window to change slowly, but as you get further away it should change more quickly. All magnetic sources look like dipoles if you get far enough away, but up close it is different. Consider the field of a solenoid (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html). Inside the solenoid the field is uniform, but as the lines come out an end, they diverge, but right outside they are nearly straight, especially near the center of an end. (The field strength is proportional to the density of lines.) Yes, and since the string to pole distance is nearly equal to the pole diameter, the window difference due to the former ought not to be very much. |
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Post by antigua on Mar 16, 2017 1:21:16 GMT -5
Mmm, I don't know. It sounds like you're saying the pickup has a more "needle" like precision at a great distance. That just seems counter intuitive. More often than not, reception becomes more diffused at a distance, unless you have a focusing agent, like a pin hole camera or a parabolic dish.
Keep in mind that the flux orientation never has to be perfectly on axis, even side ways flux constitutes change through the loop.
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Post by ms on Mar 16, 2017 5:41:50 GMT -5
Mmm, I don't know. It sounds like you're saying the pickup has a more "needle" like precision at a great distance. That just seems counter intuitive. More often than not, reception becomes more diffused at a distance, unless you have a focusing agent, like a pin hole camera or a parabolic dish. Keep in mind that the flux orientation never has to be perfectly on axis, even side ways flux constitutes change through the loop. The field diverges like a dipole further from the pole piece and so the window widens with the diverging field lines as yo get far away. It is only the component of flux pointing through a loop that contributes. "Sideways" pointing flux through the loop has no such component. |
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Post by antigua on Mar 16, 2017 9:39:07 GMT -5
Mmm, I don't know. It sounds like you're saying the pickup has a more "needle" like precision at a great distance. That just seems counter intuitive. More often than not, reception becomes more diffused at a distance, unless you have a focusing agent, like a pin hole camera or a parabolic dish. Keep in mind that the flux orientation never has to be perfectly on axis, even side ways flux constitutes change through the loop. The field diverges like a dipole further from the pole piece and so the window widens with the diverging field lines as yo get far away. It is only the component of flux pointing through a loop that contributes. "Sideways" pointing flux through the loop has no such component. Not "sideways", but at any angle other than perfectly perpendicular to the loop. Flux of course never points perfectly straight, at least not outside of a coil, so much, if not most, of the returning flux from the string will have some degree of angle to it. At a distance, the angles would likely be more extreme, but that off-axis flux would still constitute change through the loop, all the same. The main difference would be that it's less dense, because of the added distance, and because the loop is smaller when it's angled by virtue of perspective; it becomes increasingly oval, until you are 90 degrees off axis with the loop, at which point the loop looks like a straight line, and so there is no loop from that angle. Also I think we need a "system" at some point to clarify things; we're talking about "aperture widths" because it's easy, but we all know we're talking about a gradient which has no defined boundary. The rate of drop off probably has to be expressed mathematically, but I'm not a mathematician. You mentioned that -10dB means half as loud, so maybe we can define aperture width as, for a given distance between pickup and string, the distance from center, where the voltage generated is -10dBV down, from center. Another complication to keep in mind is that this boundary, however defined, it probably different depending on string gauge, because the permeable mass differs, and the boundary also likely changes as the string displaces, though that should "average out" as the string should be equal parts near and far. I'm still planning to set up a different kind of test this weekend. It just takes more free time to get this sort of thing set up. I'll tell you what I'm planning in case you see a problem; an ebow would excite a string, probably the G or D string. I'd take a single coil pickup, and mount only a single AlNiCo 5 pole piece in the pickup, I'm thinking in one of the two center-most slots, and then I'd map out dBV for measured x/y offset between the single pole piece and the excited string. |
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Post by ms on Mar 16, 2017 12:07:24 GMT -5
The field diverges like a dipole further from the pole piece and so the window widens with the diverging field lines as yo get far away. It is only the component of flux pointing through a loop that contributes. "Sideways" pointing flux through the loop has no such component. Not "sideways", but at any angle other than perfectly perpendicular to the loop. Flux of course never points perfectly straight, at least not outside of a coil, so much, if not most, of the returning flux from the string will have some degree of angle to it. At a distance, the angles would likely be more extreme, but that off-axis flux would still constitute change through the loop, all the same. The main difference would be that it's less dense, because of the added distance, and because the loop is smaller when it's angled by virtue of perspective; it becomes increasingly oval, until you are 90 degrees off axis with the loop, at which point the loop looks like a straight line, and so there is no loop from that angle. Also I think we need a "system" at some point to clarify things; we're talking about "aperture widths" because it's easy, but we all know we're talking about a gradient which has no defined boundary. The rate of drop off probably has to be expressed mathematically, but I'm not a mathematician. You mentioned that -10dB means half as loud, so maybe we can define aperture width as, for a given distance between pickup and string, the distance from center, where the voltage generated is -10dBV down, from center. Another complication to keep in mind is that this boundary, however defined, it probably different depending on string gauge, because the permeable mass differs, and the boundary also likely changes as the string displaces, though that should "average out" as the string should be equal parts near and far. I'm still planning to set up a different kind of test this weekend. It just takes more free time to get this sort of thing set up. I'll tell you what I'm planning in case you see a problem; an ebow would excite a string, probably the G or D string. I'd take a single coil pickup, and mount only a single AlNiCo 5 pole piece in the pickup, I'm thinking in one of the two center-most slots, and then I'd map out dBV for measured x/y offset between the single pole piece and the excited string. Guitar strings are all small compared to a pole piece diameter. I do not see why the string gauge would matter much for the aperture size. I say use 3db as you do for any filter. As the measurement have shown, it falls of quickly after that. These measurements respond to both intensity and angle, and so you can see how fast the combination of both factors works. |
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frankfalbo
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Post by frankfalbo on Mar 16, 2017 13:15:00 GMT -5
One pole is meaningless and will have a phase altering return path within the coil along the treble-to-bass axis. When neighboring, like-oriented poles are flanking it (for the center 4 strings) or it is against the coil edge with only one neighboring pole, the like orientation imparts rejection at the top, completely changing the shape of the field both at the string, as well as the return path. Beveled pole pieces splay the field as well, but while that affects the return path along the string axis, it exacerbates the rejection and focusing betweeen the poles. Depending on how close the pickup is, beveled magnets may have an increased, or a decreased window delta.
Also with regard to -10dB, a measley 2:1 compression Or clipping ratio knocks that down to -5dB. Rarely is guitar played through a totally linear signal path, sometimes clipping under 90dB of gain or more. This doesn't change the physical string window, but it does compress the information present, tantamount to lowering the Q.
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Post by ms on Mar 16, 2017 13:51:16 GMT -5
One pole is meaningless and will have a phase altering return path within the coil along the treble-to-bass axis. When neighboring, like-oriented poles are flanking it (for the center 4 strings) or it is against the coil edge with only one neighboring pole, the like orientation imparts rejection at the top, completely changing the shape of the field both at the string, as well as the return path. Beveled pole pieces splay the field as well, but while that affects the return path along the string axis, it exacerbates the rejection and focusing betweeen the poles. Depending on how close the pickup is, beveled magnets may have an increased, or a decreased window delta. Also with regard to -10dB, a measley 2:1 compression Or clipping ratio knocks that down to -5dB. Rarely is guitar played through a totally linear signal path, sometimes clipping under 90dB of gain or more. This doesn't change the physical string window, but it does compress the information present, tantamount to lowering the Q. There is a reason why we take this slowly and go through one step at a time. Does anything you just wrote cast doubt on the measurement that I made showing approximately where the string magnetization in the direction along the string is 3 and 10 db down? I do not understand what you wrote, and I do science for a living mostly, electro magnetic type of stuff, and I started this off by pointing out that there are two sorts of approximate answers, width of the pickup, or with of the string, the first a result of "expert" opinion, the second indicated by theoretical analysis. Does what you are saying affect the validity of the evidence so far that it is the width of the pole piece that is important? "One pole is meaningless and will have a phase altering return path..." There is no phase to alter; what do you mean? |
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frankfalbo
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Post by frankfalbo on Mar 16, 2017 14:40:02 GMT -5
Antigua is preparing to measure treble-to-bass window, possibly as it relates to drop off when bending between poles, by using only one pole piece in a coil. You don't see the problem with that? One pole, with its own unaltered return path and productive coil body on either side of it?
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Post by antigua on Mar 16, 2017 15:05:53 GMT -5
When I conduct my test, I will (at least in this case) be careful not to say "because this test reveals X, all pickups have a window size commensurate to X". The test only speaks for it's own circumstance, and it will only be the first test to come, it will be contrasted with further tests. As a matter of fact, also planned is putting pole pieces beside the test pole piece, as well as using steel pole piece(s) with a magnet on the opposite side to see if the higher permeable steel influences the relationship between dBV and distance. I usually take lots of pictures, too, so that's like a few thousand more words by itself. The hard part as I see it will be getting the pickup to rest in fixed positions relative to the string. There are a lot of ways to do it, and most of them are delicate and kind of a hassle.
Regarding the -10dB becoming -5dB, I agree that this is very likely, and I mentioned above the notion that compression might effectively change the aperture width. It's all rather vague at this point. I'd rather be collecting data than talking about it, it's just that typing some thoughts is 1000x times easier than dealing with the practical setups, so there's more imbalance than I'd care for in this regard.
I'd like to get better with FEM and model this the way we model RLC circuits, but I installed FEM and it seemed to be very difficult to use, so I have a ways to go with the learning curve there. I think FEM could be highly insightful. I've seen other people use it in guitar pickup contexts, but I haven't seen anyone model exactly what I'm looking to have modeled in this case; the magnetic field of a string, over a pole piece, at varying distances. The other problem is that FEM appears to model static magnetic fields, and what we really require is the delta that is brought about by string displacement, not the sum of a static magnetic circuit.
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Post by ms on Mar 16, 2017 15:10:00 GMT -5
Antigua is preparing to measure treble-to-bass window, possibly as it relates to drop off when bending between poles, by using only one pole piece in a coil. You don't see the problem with that? One pole, with its own unaltered return path and productive coil body on either side of it? I believe he is not interested in string bending itself so much but rather he is using this technique as a way of measuring the sensitivity versus location of one pole piece. Thus I think he is doing what he wants. He will see string magnetization fall off, and he will see loss of flux from the vibrating string through the pole piece. It is true that he will see some flux from through the coil without the pole piece, but we have no perfect way of measuring the fall off along a string. This seems useful to me, but maybe he can give you a better idea what he is doing. |
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Post by antigua on Mar 16, 2017 15:14:39 GMT -5
I understand that string bending is imperfect because it's receives an assist form the neighboring pole piece. hence the need for a test with a single pole piece.
The basic question is this: when the pickup with one pole piece has its pole piece X millimeters off asix with, and Y millimeters above, the moving string, the dBV is Z. I will have to create a table of X by Y = Z to contain the results.
The reason I think this test is informative, is because we're wondering how far the magnetic "reach" is out along the length of the string. There is no "assisting" magnet outwardly, along the string.
ms, regarding your test, I do think I have a clear picture in my head of what you did, but I had to paint a mind picture with words. I'm really curious to see if the test I had in mind agrees with your overall results, and then I'd worry more about the specific of what you had done at that point in time, in order to see why our results were different, or the same.
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frankfalbo
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Post by frankfalbo on Mar 16, 2017 16:27:04 GMT -5
I understand that string bending is imperfect because it's receives an assist form the neighboring pole piece. hence the need for a test with a single pole piece.. The variable you're missing is that it's not just an assist. It's a null. Let's pretend we're referring to flat poles, no stagger. The assist is vertical by focusing the field, but depending on how close the pickup is to the strings, you're coming in and out of a null. With the pickup far from the strings you have a smeared convolution. Come closer and you'll have 6 focused, concentrated zones with convolution in between, some overlap. Closer still and you'll find the null/dead zone. None of which you'll see during this first rudimentary look. Compound that by the comb filtering associated with one lone pole, mid-coil, generating non-standard audio into the coil in association with its return path. My point is, you won't have a clean number on the amplitude delta across the lateral axis because it's height dependent and altered by neighboring poles. Drive it with a tine like a Fender Rhodes if you want to get a 3 dimensional dB plot. |
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Post by ms on Mar 16, 2017 16:59:08 GMT -5
I understand that string bending is imperfect because it's receives an assist form the neighboring pole piece. hence the need for a test with a single pole piece.. The variable you're missing is that it's not just an assist. It's a null. Let's pretend wends referring to flat poles, no stagger. The assist is vertical by focusing the field, but depending on how close the pickup is to the strings, you're coming in and out of a null. With the pickup far from the strings you have a smeared convolution. Come closer and you'll have 6 focused, concentrated zones with convolution in between, some overlap. Closer still and you'll find the null/dead zone. None of which you'll see during this first rudimentary look. Compound that by the comb filtering associated with one lone pole, mid-coil, generating non-standard audio into the coil in association with its return path. My point is, you won't have a clean number on the amplitude delta across the lateral axis because it's height dependent and altered by neighboring poles. Drive it with a tine like a Fender Rhodes if you want to get a 3 dimensional dB plot. I do not understand the null you mention, nor the comb filtering associated with one lone pole. |
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Post by antigua on Mar 16, 2017 18:09:15 GMT -5
I'm not sure what is meant by "null", but there is a sum polarity between the pole pieces at the elevation of the string:  |
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frankfalbo
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Post by frankfalbo on Mar 16, 2017 18:55:37 GMT -5
Not with that meter.
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Post by antigua on Mar 16, 2017 22:00:52 GMT -5
Since this is such an active topic I couldn't help but do this sooner than later. Here are the results of my experiment. The values are in dBm, as reported by the Vellemam PSCGU250, which the pickup is connected to. The reference string is the "G" string, with an ebow parked over the 12th fret. I placed the pickup directly over the G string, 3mm above, and recorded the dBm value, then slid pickup 3mm away from the G string, recorded the value, etc. until I got to 15mm away, then I raised the pickup to 6mm above the string, and repeated the process, and again and again up to 15mm above the string. The pickup has a single AlNiCo 5 pole piece, but it requires some distance. Reading the table across shows dBm by offset distance from center, and reading down is dBm by height between the pickup pole piece and the string. The pole piece is inserted into the bobbin so that it's flush with the plastic. | offset mm | 0 | 3 | 6 | 9 | 12 | 15 | | height mm | | | | | | | | | 3 | | -26.2 | -30.0 | -36.3 | -45 | -49 | -49 | | 6 | | -33.1 | -33.6 | -37.6 | -42.5 | -46 | -50 | | 9 | | -39.3 | -39.0 | -40.7 | -43 | -44 | -44.7 | | 12 | | -41.7 | -42.0 | -42.6 | -43.3 | -44.1 | -45.4 | | 15 | | -44.3 | -44.2 | -44.0 | -44 | -45 | -45 |
What's striking to me is how when the pickup is farther away, a constant dBm is maintained for a wider offset. I made the values bold and red where the dBm holds fairly constant before dropping off. At 3mm pole piece to string distance, the amplitude drops immediately with added offset, -26 to -30 to -36. But at 6mm distance, it hold at -33 at both 0mm and 3mm offsets, then drops off to -37 at 6mm. Same thing but even more dramatic at 9mm, -39, then -39 again, then -40, and finally at 9mm offset it drops to -43. 12mm and 15mm distances show the same trend, but come increasingly close to the noise floor, and become more ambiguous. It looks to me like greater distance does equate to a wider magnetic reach. The pole piece's overall diameter is about 4.5mm, so an offset of 3mm off-center is already outside of the pole piece's circumference. So if the pickup is close to the string, it seems that the aperture width is about as wide as the pole piece, but with the pickup lowered, if expands beyond the pole piece a bit, but with a radius that is effectively not much more than 3mm, for a total aperture width of about 6mm, at 6mm pole piece to string distance. As far as comb filtering goes, messing with this www.till.com/articles/PickupResponseDemo/index.html shows that you don't get much variation in amplitude below 5kHz unless the aperture is greater than an inch wide, which is 25mm, well in excess of a practical aperture of 3mm to 6mm, when you have a guitar pickup set 3mm to 6mm away from the strings. I'll try this experiment again with a steel pole piece, and see if flux density changes anything, by adding additional neo's to the opposite side of the steel pole piece. Here are pictures of the setup:     |
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Post by wgen on Mar 17, 2017 6:03:26 GMT -5
That's much interesting...well, I hoped that simply lowering the pickup (or, making the distance between string and the pole piece greater, in this case) would make a bigger tonal difference, in terms of comb filtering and tone shaping...I thought that I could eventually achieve a more humbucker like response from a single coil, but this test demonstrates that's impossibile with lowering the pickup only I guess  In your opinion, the fact that in this case the magnet IS the pole piece, being an Alnico 5 single rod, could be any different from having a ferrite pole piece above a magnet bar underneath...? In other words, would the distance between the string and the pole make for different behaviour in harmonics sampling if you had, let's say, a P90 (which usually have pole pieces with magnet underneath), instead of the strat type of single coil as the "sampler"? |
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Post by ms on Mar 17, 2017 7:40:59 GMT -5
Since this is such an active topic I couldn't help but do this sooner than later. Here are the results of my experiment. Very nice! One way to describe the variation of the window with distance up from the pickup would be this: As you start from far away, the window is broad and narrows as you get closer. But as you get very close the narrowing slows down. This is because the magnetic source now appears extended rather than like a single dipole. The length and permeability of the pole piece have an effect on the shape of the field, and so they are expected to play some rolel in where the window stops getting narrower. Your measurement nicely captures both effects I described, magnetization of the string and induction in the coil. I am looking at the second effect now since I like to be able to see the two effects separately if possible.. |
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Post by antigua on Mar 17, 2017 10:11:23 GMT -5
That's much interesting...well, I hoped that simply lowering the pickup (or, making the distance between string and the pole piece greater, in this case) would make a bigger tonal difference, in terms of comb filtering and tone shaping...I thought that I could eventually achieve a more humbucker like response from a single coil, but this test demonstrates that's impossibile with lowering the pickup only I guess In your opinion, the fact that in this case the magnet IS the pole piece, being an Alnico 5 single rod, could be any different from having a ferrite pole piece above a magnet bar underneath...? In other words, would the distance between the string and the pole make for different behaviour in harmonics sampling if you had, let's say, a P90 (which usually have pole pieces with magnet underneath), instead of the strat type of single coil as the "sampler"? I'm going to repeat this test later with steel pole pieces. The theory says it should be no different, so it will be fun to see if a practical test agrees or not. Also, regarding compression as a means of widening aperture width, it looks like there might still be something to that, but looking at the rate of dB drop off for a given offset, a +5dBm boost appears to only win about and extra 3mm radius / 6mm diameter of "window", still coming nowhere near the 1 inch window that supposedly allows for audible filtering effects. |
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Post by wgen on Mar 17, 2017 10:44:31 GMT -5
That's much interesting...well, I hoped that simply lowering the pickup (or, making the distance between string and the pole piece greater, in this case) would make a bigger tonal difference, in terms of comb filtering and tone shaping...I thought that I could eventually achieve a more humbucker like response from a single coil, but this test demonstrates that's impossibile with lowering the pickup only I guess In your opinion, the fact that in this case the magnet IS the pole piece, being an Alnico 5 single rod, could be any different from having a ferrite pole piece above a magnet bar underneath...? In other words, would the distance between the string and the pole make for different behaviour in harmonics sampling if you had, let's say, a P90 (which usually have pole pieces with magnet underneath), instead of the strat type of single coil as the "sampler"? I'm going to repeat this test later with steel pole pieces. The theory says it should be no different, so it will be fun to see if a practical test agrees or not. Also, regarding compression as a means of widening aperture width, it looks like there might still be something to that, but looking at the rate of dB drop off for a given offset, a +5dBm boost appears to only win about and extra 3mm radius / 6mm diameter of "window", still coming nowhere near the 1 inch window that supposedly allows for audible filtering effects. Yeah that's the same thing I thought after reading your test and having tried various "pickup width" apertures in the Tillman demo...there should be a much higher aperture to achieve a real difference I guess..! Not to say that in practice I won't be able to go lower than a certain height with pickups, trying to achieve a greater distance from the strings...so it seems to me that, for most applications, what other players hear as "a world of difference" when they talk about different pickups heights, they're mostly referring to the effects of a stronger signal of a pickup closer to the strings versus a weaker signal, which obviously may have an influence on the rest of their signal chain (overdrives clipping more or less, tubes in the amplifier compressing more or less, and so on..) |
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Post by antigua on Mar 17, 2017 11:34:15 GMT -5
I'm going to repeat this test later with steel pole pieces. The theory says it should be no different, so it will be fun to see if a practical test agrees or not. Also, regarding compression as a means of widening aperture width, it looks like there might still be something to that, but looking at the rate of dB drop off for a given offset, a +5dBm boost appears to only win about and extra 3mm radius / 6mm diameter of "window", still coming nowhere near the 1 inch window that supposedly allows for audible filtering effects. Yeah that's the same thing I thought after reading your test and having tried various "pickup width" apertures in the Tillman demo...there should be a much higher aperture to achieve a real difference I guess..! Not to say that in practice I won't be able to go lower than a certain height with pickups, trying to achieve a greater distance from the strings...so it seems to me that, for most applications, what other players hear as "a world of difference" when they talk about different pickups heights, they're mostly referring to the effects of a stronger signal of a pickup closer to the strings versus a weaker signal, which obviously may have an influence on the rest of their signal chain (overdrives clipping more or less, tubes in the amplifier compressing more or less, and so on..) I don't think this rules out tonal consequences of proximity, but it does appear that it takes any credit away from comb filtering. To my ear, there is a lot of tonal difference with pickup height. It seems that I hear 1) more bass and 2) more tonal fluctuation with time, when a pickup is closer to the strings. Maybe the reason there would be more bass when the pickup is closer is due to the higher permeability of the lower wound strings, so closer pickup = even stronger magnetized string. Maybe I should repeat this test on a lower wound string before I move on to other pole piece types. The other thing, when a pickup is closer to the strings, it sounds like the tone "evolves" more, as if a wah wah pedal was being rocked very slowly. If you look at a guitar string when you pluck it, you can see its movement pattern change with time as it decays, because when you pluck it, you pluck it in a particular direction with a lot of force, and the string rebounds from that initial vector force as it vibrates. The test above shows that when the string an pole piece and coil are all close, it has a narrower aperture. My suspicion is that the narrow aperture causes that evolving rebound movement to have a more pronounced effect on the tone, and when the aperture is wider, it has a less profound effect. I can't prove that, though. I just see a correlation at this point. Here's a video someone made in January demonstrating pickups heights. Towards the middle of the video, he lets the strings ring out longer, and I think you can hear more of that "slowly rocked wah" tone when the pickup is closer to the strings. |
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