psw Posted September 21, 2007 Report Share Posted September 21, 2007 psw, believe what you want, but it is the ironand nickel in the guitar string that changes the magnetic field, not the nickel/steel becoming magnetic itself. If you take some time to learn about the physics, you would see that the only way something put in a magnetic field can make a a big difference is by becoming magnetized. Magnetic field are produced by currents. All materials have atomic currents. In ferromagnetic materials these small current domains can line up to reinforce each other and have a big effect. Yes...what is a common magnet but a ferromagnetic material with high permeability? Alnico is an alloy that will hold it's magnetic state well once magnetized...generally these are used in pickups demagnetized and magnetized by attaching a strong magnet to them to align the domains as Mike suggests. They are not intrinsically magnetic, nor is ceramics, etc. "If you take some time to learn about the physics"...while it is true the hard sciences are not my strong point, a lot of my intuition and what I have garnered from texts on the broader subject (not just the internet) as well as many conversations here like this. It is very helpful to have such conversations to iron out my own fallacies as well as those of others A lot of my "knowledge" though comes from actual experimentation with precisely these issues, and FEMM modeling too! I still think this part of the conversation....a little silly... The amount of the string that is magnetized, and what the string is doing within that area (or shape) is very important. pete But the wide sampling as related to the width of the coil does not stand up to analysis. Look at the FEMM plots on page one. For both the P-90 and the Fender type, the magnetic field has a large vertical component only very nearly over the pole piece. Away from the pole piece, the field becomes weaker and more horizontal. Remember, it is only the vertical component (that is, perpendicular to the plane of a loop of wire) that matters. "Remember, it is only the vertical component (that is, perpendicular to the plane of a loop of wire) that matters." I am not so sure about that. kids want me will come back with an edit when I can...I know what youare saying mike... p Quote Link to comment Share on other sites More sharing options...
Sock Puppet Posted September 21, 2007 Report Share Posted September 21, 2007 Hi, sorry to butt in. Here's an ancient pickup patent - the strings are first magnetised by connecting the pickup to a battery: http://www.google.com/patents?id=QoMWAAAAE...strings#PPP2,M1 If you make a pickup with iron slugs and no magnet, it will work (though a little weak) if you first magnetise the strings with a permanent magnet. Magnets. Very strange. S. Quote Link to comment Share on other sites More sharing options...
SwedishLuthier Posted September 22, 2007 Report Share Posted September 22, 2007 Lot of thoughts here guys, but when you are referring to "hard science" without any directions to that particular science I always ask the question: “Very interesting, can you tell me more?”. I agree with psw as I think that the discussion a bit unbalanced. Can we please stay away from the“I know more that you because I have a degree” stuff. We do not know who is on the other on of that internet nick…Might be a university professor…And please put some faith in good old first hand experience too… Anyway I am really interested in Mikes statement that it is only the vertical part of the magnetic field that is important. I’m not really following your there do you mind expanding those thoughts? And welcome to the forum Sock puppet. I recognize you from the pickup winders forum. The old "String vision" pickup for acoustics were made in a similar way, using a manget to magnetize the strings permanently Quote Link to comment Share on other sites More sharing options...
Mike Sulzer Posted September 22, 2007 Report Share Posted September 22, 2007 Peter and Pete, Why is it the vertical component that matters? Remember the equation that Peter posted near the beginning of this thread? It contained the time rate of change of the flux, phi. To understand what this flux is, go to "faraday's law of induction" in Wikipedia, and look at the first equation. The left side says "the voltage around a loop". The right side says "the negative of the time rate of change of the result of adding up some stuff". The result of adding up that stuff is the flux, phi. The stuff is the "dot" product of B at each point (on the surface enclosed by the loop) and "dA". B is a vector, meaning it has a direction and a magnitude. "dA" is also a vector. It can be thought of as a very small piece of the surface where we are looking at B. The direction of dA is defined as perpendicular to the surface at that point. The dot product says take the two vectors that surround the dot, and if their directions are perpendicular, the result is zero. If they are parallel, the result is just the product of the magnitudes of the vectors. For directions in between, the result is less than the product of the magnitudes, depending on how much their directions differ. In our case if we think of vertical as away from the surface of the guitar, that is, the direction of the long axis of the pole piece, dA is in this direction. So the vertical part of the magnetic field is what matters. Quote Link to comment Share on other sites More sharing options...
psw Posted September 22, 2007 Report Share Posted September 22, 2007 I know what you mean Mike...but I have always considered the whole field as a circuit so that although the coil only "picks up" the changes in the magnetic field going through the core...surely the field that surrounds it...the connection between the north and south, top and bottom and hence across the top with the strings, has some influence on what happens in the vertical core of the coil? I have similar "feelings" about the connectiveness of the whole coil, not just the upper portion of it having the major influence... Lot of thoughts here guys, but when you are referring to "hard science" without any directions to that particular science I always ask the question: “Very interesting, can you tell me more?”. I agree with psw as I think that the discussion a bit unbalanced. Can we please stay away from the“I know more that you because I have a degree” stuff. We do not know who is on the other on of that internet nick…Might be a university professor…And please put some faith in good old first hand experience too… +2 pete Quote Link to comment Share on other sites More sharing options...
Mike Sulzer Posted September 23, 2007 Report Share Posted September 23, 2007 I know what you mean Mike...but I have always considered the whole field as a circuit so that although the coil only "picks up" the changes in the magnetic field going through the core...surely the field that surrounds it...the connection between the north and south, top and bottom and hence across the top with the strings, has some influence on what happens in the vertical core of the coil? I have similar "feelings" about the connectiveness of the whole coil, not just the upper portion of it having the major influence... pete But the law of induction is the complete story as far as the voltage around the loop. We just have to determine the component of the fluctuating field through the coil: 1. The permanent magnetic field from the core temporarily magnetizes the string near the core. We know from the FEMM plots that the vertical component of the string magnetization falls off rapidly with distance along the string away from the core. (Details could be provided with additional modeling.) 2. The field from any small magnet is like that of a magnetic dipole except very close to it. Thus the field falls off as the cube of distance except very near the "string magnet". 3. How is the fluctuating component generated? When the string moves up and down the field moves with it. Since the field falls off with distance. The field through the coil changes. If the field did not fall off with distance, the field through the coil would not change and the pickup would not work. 4. The core guides the field lines through the coil, amplifying the field and slowing the fall off. But it mostly affects the field lines that enter right from above it. The result is that the vertical component of the fluctuating component of the magnetic field through the core comes from the area not too far from right over the core. So the pickup does not sample over the full part of the string over the coil, only near the core. Quote Link to comment Share on other sites More sharing options...
JoeAArthur Posted September 23, 2007 Report Share Posted September 23, 2007 Wow... this has risen from a slight sniff of bs, to full blown BS - amazing!! Cool. Can't wait to see how it develops!! Only problem is the people that might be buffaloed into thinking it really means something because of all the psyco-non-technical-babble. If you can't provide a reasonable and easily understandable explanation - then it is hype. Please continue Mike - sorry for the interruption. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.