Polished vs Un-polished Magnets

[frankfalbo]

David- Saying a pickup sounds "cold" also doesn't fit Webster's definition. My use of the term dithering is in reference to the magnetic "hash" occurring across a multi dimensional surface parallel to the polar pattern.

Think it through by magnifying the variable to the point of absurdity. Suppose these surfaces of the magnet were cut into a sawtooth shape, like a single cut mill file. Those "teeth" would send off their own stray fields. You might expect that since each tooth was close to the next tooth, the the field would remain in alignment, but this would really only be true if they were perfectly cornered straight cuts. With a 45 degree angle (for example) the field would start to spray upward, and then be in minor conflict with the next saw tooth.

A rough cut Alnico doesn't have uniform deformity like a sawtooth or even an egg carton. It can look like an English muffin. That has to introduce "flux noise" across the surfaces.

Again my disclaimer; I can hear the differences in controlled tests, as well as my own guitars at my home shop, but concede that it is very far down on the list of variables and I have no qualms with anyone who wants to make pickups as if it means nothing at all.

[David King]

Presumably they would be grinding them with a water-based coolant so the heating would be limited to below the boiling point but it might be worth asking about. Alnico is the most heat-tolerant magnetic material, it can easily 800ºF without changing properties.

[David Schwab]

A rough cut Alnico doesn't have uniform deformity like a sawtooth or even an egg carton. It can look like an English muffin. That has to introduce "flux noise" across the surfaces.

But that's on the side of the magnet. I don't see where that has any bearing on what comes out of the two poles. That's why the poles are always ground smooth.

[David King]

A surface grinder would also use a magnetic plate to hold the parts in place during the grinding. A mag plate will definitely magnetize the alnico partially. The plate field is switched on and off mechanically with a lever on the side of the plate and uses permanent magnets. I'm sure there are some that use electromagnets and they may even run on AC so they would tend to demagnetize the part on release as long as the field is allowed to decay slowly enough.

[frankfalbo]

You have to stop thinking of these magnets as only having an influence over what happens at the top of the coil in the string window. If you planted a coil underneath your humbucker, like where a stacked single bottom coil would go, it would make some sound right? So without another giant post, "stuff" is happening down there in sympathy to the disturbances up top.

[salvarsan]

A rough cut Alnico doesn't have uniform deformity like a sawtooth or even an egg carton. It can look like an English muffin. That has to introduce "flux noise" across the surfaces.

What's your opinion of the purposeful field non-uniformity of AGI's Lace Sensors or Holy Grails?

[Mike Sulzer]

You have to stop thinking of these magnets as only having an influence over what happens at the top of the coil in the string window. If you planted a coil underneath your humbucker, like where a stacked single bottom coil would go, it would make some sound right? So without another giant post, "stuff" is happening down there in sympathy to the disturbances up top.

If I see what you mean (and maybe not since I missed your meaning above) this is not at all how it works. The lower coil of a stacked humbucker produces signal because time varying flux from the vibrating string makes it down there, guided by the pole pieces. The permanent magnetic field does not play any role down there. So when you write "You have to stop thinking of these magnets as only having an influence over what happens at the top of the coil in the string window." that is not correct if you mean what it appears to say. The function of of the permanent field is to magnetize the string. The magnet itself can also play a role as part of the ac circuit as a result of its permeability (increasing the inductance) and conductivity (resulting in eddy currents), but that is a different function, one independent of the permanent field.

For example, a ceramic magnet has essentially no conductivity and low permeability, and a neo has nearly the permeability of a vacuum, and low conductivity (compared to steel, for example). They provide a strong permanent field to magnetize the pole pieces which magnetize the strings, but have very little other function. Alnico is more conductive and has a significant permeability, although much lower than steel, and so it has a somewhat greater role to play in the ac circuit.

[frankfalbo]

Mike I've seen you go down this road in the past, I don't want to do it. You have very strong academic views of what can and can't affect the sound of pickups, and why. Sometimes they are out of sync with my experiences, and sometimes out of sync with views held by very intelligent associates of mine both in and out of the music industry. No big deal, some people swear Diet Dr Pepper tastes the same as regular. To them it does.

[Mike Sulzer]

Mike I've seen you go down this road in the past, I don't want to do it. You have very strong academic views of what can and can't affect the sound of pickups, and why. Sometimes they are out of sync with my experiences, and sometimes out of sync with views held by very intelligent associates of mine both in and out of the music industry. No big deal, some people swear Diet Dr Pepper tastes the same as regular. To them it does.

What affects the sound of a pickup is only part of it, and not what I was referring to in the message you just responded to. What is in question here is the physics: what is a proper description of how a pickup works? Well, it is not what you said, and responding to what I wrote as if it is a matter of opinion is inappropriate. It is not opinion, it is fact. The physics of how to describe magnetism was long ago settled. What I wrote was not an academic view, it is a statement of how it works. Anyone who understands E&M will tell you essentially the same thing.

[David King]

Are there other's here besides Frank who think they can hear a difference? Seems like either there's an audible difference or there isn't. If we can come to a gentleman's agreement that there *might* be an audible difference then I think we can move on to the crux of this argument which I take to be "why is there a difference"?

[David Schwab]

Are there other's here besides Frank who think they can hear a difference? Seems like either there's an audible difference or there isn't. If we can come to a gentleman's agreement that there *might* be an audible difference then I think we can move on to the crux of this argument which I take to be "why is there a difference"?

The first thing that would beed to be done is to establish that we have two magnets that are the same, except one is ground. They would have to have the same dimensions, same weight, and measure the same charge.

If we are using two magnets that don't behave the same, then the pickups will sound different. So if one s stronger for example, that will be something you hear. Ad that will have nothing to do with the texture of the sides of the magnet.

[Mark Hammer]

What you describe is, of course, the bane of virtually ALL guitar/bass-related gear discussion. Take two people comparing exactly ONE example of something that is presumed to be different in precisely ONE nominal way (ignoring all possible tolerances and unit-to-unit differences), add "the internet", published interviews with inarticulate "stars", bad ad copy, ill-informed music store staff, stir, and out comes tons of unsupported/untested assumptions about what that nominal characteristic is responsible for.

Let me be clear that I am not suggesting this is what Frank's observations emerge out of. Rather, it is simply a common-enough occurrence that I understand why many roll their eyes almost reflexively when things like this come up.

[Joe Gwinn]

The sides of a magnet don't really have a field. That's the rough part. The poles on a rough cast magnet are ground smooth. That's where the field is.

Not really. There is always "leakage flux" coming out or going into the sides. Actually, the technical definition of leakage flux is a bit slippery - it's just the flux in places you don't want flux.

More generally, the difference in magnetic permeability of an insulator (like air) and a good conductor (like mild steel) is about 1000 to one, so there are always leakage paths, no matter what one does.

By contrast, for electric currents, the ratio is at least millions to one.

[Mike Sulzer]

David, if you want to check what Joe said, take a humbucker magnet and a small flat head steel screw. The head sticks nicely to either pole, but also a sticks less forcefully to the side. Therefore there is a field.

You can think of a magnet as composed of lots little current loops. Each little loop is a dipole. Concentrated field lines pass through the loop, spread out and return through the other end. Think of adding up the fields of all the dipoles (allowing for magnitude and direction). There has to be a field everywhere, but yes, it is strongest at the poles.

Not really. There is always "leakage flux" coming out or going into the sides. Actually, the technical definition of leakage flux is a bit slippery - it's just the flux in places you don't want flux.

More generally, the difference in magnetic permeability of an insulator (like air) and a good conductor (like mild steel) is about 1000 to one, so there are always leakage paths, no matter what one does.

By contrast, for electric currents, the ratio is at least millions to one.

[frankfalbo]

Mike it seemed like you were disagreeing with me but now validating my statements with this last post. Perhaps where we part is the notion that disturbance at the string sets off reactionary disturbances elsewhere in the magnetic circuit, which penetrate the coil. If you concede to that, then its a pretty short jump to concede that texture across the surface that is pressed right up against the bottom of the coils could behave differently than a smooth, flat surface. For that matter (though this is from a different thread about air gaps) you can see how disturbances that happen within a air gap could penetrate the coil too, and that its not just about the reduced gauss strength at the string.