Polished vs Un-polished Magnets

[big_teee]

So, with rough cast, vs rough cast that's been machined, do we think this is strictly cosmetic?
Or does one exhibit better highs than the other?
That is what is constantly discussed on the Magnet Swappers Forums.
Maybe the Comment that Frank made, about what the gauss is after it stablizes is the main answer.
I still think that Gauss strength is gauss strength as long as it is coming from similar metallic Magnets?
It seems that my A2 Rough bar mags, charge a little hotter than the machined A2s I have?
T

[Mike Sulzer]

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.

Well, that is a pretty big parting of the ways. I hear you saying that if there is a field from the magnet under the pickup, then there is an effect that simply does not happen if there is no field; that is, the vibrating string somehow disturbs that field, resulting in secondary disturbances through the coil. That does not happen. Linearity applies here; the field under the pickup simply adds with the field from the vibrating string that exists there also. This means that you can conceptually subtract off the permanent field, that is, set it to zero, without affecting the results. (Note that the magnet can otherwise affect the circuit through its permeability, a property that it has even if the magnet is not "charged", although it might be somewhat different in value.)

It is often said that the pickup explanation using reluctance justifies what I hear you saying. It does not, and this misunderstanding shows the danger of trying to derive intuitive understanding from a secondary analogy rather dealing directly with the basic physics (Maxwell's equations, in particular the one that has the law of magnetic induction within it).

What we are discussing is well understood physics. There is no room for opinion or differing interpretations.

[ScottA]

Well, that is a pretty big parting of the ways. I hear you saying that if there is a field from the magnet under the pickup, then there is an effect that simply does not happen if there is no field; that is, the vibrating string somehow disturbs that field, resulting in secondary disturbances through the coil. That does not happen. Linearity applies here; the field under the pickup simply adds with the field from the vibrating string that exists there also. This means that you can conceptually subtract off the permanent field, that is, set it to zero, without affecting the results. (Note that the magnet can otherwise affect the circuit through its permeability, a property that it has even if the magnet is not "charged", although it might be somewhat different in value.)

It is often said that the pickup explanation using reluctance justifies what I hear you saying. It does not, and this misunderstanding shows the danger of trying to derive intuitive understanding from a secondary analogy rather dealing directly with the basic physics (Maxwell's equations, in particular the one that has the law of magnetic induction within it).

What we are discussing is well understood physics. There is no room for opinion or differing interpretations.

So then, back to my point. Let's assume that the observation is correct: there is a tonal difference between rough and smooth.

Where then would the difference come from? Things like property differences as a consequence of the grinding process (I would think that even with good cooling you could still have at least localized compositional or micro-structural changes, etc) or a change in the response of the magnetic circuit as a function of effective air gap would still be in play.

I mean, even assuming that the observation is correct, we're talking about subtle stuff here, right?

[David Schwab]

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.

Well you can see that then you look at the magnetic field with something, but obviously in the middle of the magnet is a null point. Orienting a magnet's poles the "wrong way" in a pickup, i.e., not facing the pickup's pole pieces, gives you a pickup that doesn't work very well. So there is not much useable flux on the sides. Same is true with ground or cast magnets.

So how would surface texture affect this?

[David Schwab]

So, with rough cast, vs rough cast that's been machined, do we think this is strictly cosmetic?
Or does one exhibit better highs than the other?
That is what is constantly discussed on the Magnet Swappers Forums.
Maybe the Comment that Frank made, about what the gauss is after it stablizes is the main answer.
I still think that Gauss strength is gauss strength as long as it is coming from similar metallic Magnets?
It seems that my A2 Rough bar mags, charge a little hotter than the machined A2s I have?
T

How do you define "better highs"? More high frequency contact? "Smoother" high frequency content?

They have magnet swapping forums‽

If you are swapping magnets, the usual affect is magnets of different strengths. So to generalize, if you want brighter use a stronger magnet, like an Alnico 5, 8, or ceramic. If you want warmer use a weaker magnet like an Alnico 2. I often swap out magnets in my own guitar pickup designs to see which gets me the tone I want. Sometimes i make something with a ceramic 8, and then decide it's too harsh in the upper mids, so without rewinding it I just swap the magnet for an alnico 2 or something.

I don't use a lot of alnico, but I am just starting to. You will hear people say that alnico of the same grade from different manufacturers sounds different. That makes sense if the mixture of the alloy differs.

I also have to mention that my only experience with the cast magnets is when I was rewinding older Gibson pickups. I have not used any in my own pickups.

Here's a question; are cast and ground alnico magnets made with the same alloy?

[big_teee]

How do you define "better highs"? More high frequency contact? "Smoother" high frequency content?

They have magnet swapping forums?!

If you are swapping magnets, the usual affect is magnets of different strengths. So to generalize, if you want brighter use a stronger magnet, like an Alnico 5, 8, or ceramic. If you want warmer use a weaker magnet like an Alnico 2. I often swap out magnets in my own guitar pickup designs to see which gets me the tone I want. Sometimes i make something with a ceramic 8, and then decide it's too harsh in the upper mids, so without rewinding it I just swap the magnet for an alnico 2 or something.

I don't use a lot of alnico, but I am just starting to. You will hear people say that alnico of the same grade from different manufacturers sounds different. That makes sense if the mixture of the alloy differs.

I also have to mention that my only experience with the cast magnets is when I was rewinding older Gibson pickups. I have not used any in my own pickups.

I said pickup swapping forums.
Actually more of guitar forums, that get to ranting on magnet swapping.
I was just trying to de Myth the concept, and was going to do some referring to this thread.
I think the difference being heard is mainly difference in Gauss strength.
I told one group, unless you have a way to measure gauss, and a way to remagnetize, Their so called tests are a shot in the Dark.
Not sure what they are referring to" adding highs, and sucking the highs out of", means either.
They say the shiny has more highs that the rough.
Thanks,
T

[David Schwab]

I said pickup swapping forums.

No you didn't.

That is what is constantly discussed on the Magnet Swappers Forums.

You mean you meant to say pickup swapping forums. I was just thinking that was a very niche forum. I could see them trading magnets and stuff.

Actually more of guitar forums, that get to ranting on magnet swapping.
I was just trying to de Myth the concept, and was going to do some referring to this thread.
I think the difference being heard is mainly difference in Gauss strength.
I told one group, unless you have a way to measure gauss, and a way to remagnetize, Their so called tests are a shot in the Dark.
Not sure what they are referring to" adding highs, and sucking the high" means either.
They say the shiny has more highs that the rough.
Thanks,
T

The differences are the strength of the magnet, and the type of magnet it is.

Adding highs would be brighter. This is why they often use ceramic magnets in over wound pickups. The magnets bright out more high end. But then some people like dark sounding over wound pickups, and you will find those with alnico 2s and 5s. I dislike dark humbuckers. I have a tone control if I want to darken up the sound!

[Mike Sulzer]

...but obviously in the middle of the magnet is a null point.

I think I see why you say that, but that is not how it works. Field lines run sort of straight through the magnet with a density that does not change too much. This means that the field is pretty much constant (not exactly, of course) through the magnet.

Orienting a magnet's poles the "wrong way" in a pickup, i.e., not facing the pickup's pole pieces, gives you a pickup that doesn't work very well. So there is not much useable flux on the sides. Same is true with ground or cast magnets.

If you orient the magnet the wrong way as you suggest, the field is indeed lower in magnitude, but it is also pointing the wrong way. It needs to be pointing along the pole piece, not sideways. When you magnetize the string, it is the component of the changing field that points down through the coil that counts. When the magnet has field lines pointing the wrong way, you do not get the string magnetized strongly in the correct direction, and you do not get much signal. It is really the direction that is the problem. Did you check the field strength along teh side with some steel?

[Mike Sulzer]

I agree that subtle it would be, that being the largest expected effect. It is the sort of thing I might not be able to hear, but who knows unless you make a real effort to do the tests right.

So then, back to my point. Let's assume that the observation is correct: there is a tonal difference between rough and smooth.

Where then would the difference come from? Things like property differences as a consequence of the grinding process (I would think that even with good cooling you could still have at least localized compositional or micro-structural changes, etc) or a change in the response of the magnetic circuit as a function of effective air gap would still be in play.

I mean, even assuming that the observation is correct, we're talking about subtle stuff here, right?

[David Schwab]

I think I see why you say that, but that is not how it works. Field lines run sort of straight through the magnet with a density that does not change too much. This means that the field is pretty much constant (not exactly, of course) through the magnet.

Yes, it runs through the magnet, but exits out the poles. You don't really get things to stick to a magnet between the poles.

But yes, clearly here you can see it looping around the sides.

[frankfalbo]

That's the free standing magnet though. Once you attach additional circuitry to either side those lines begin to "have somewhere to go".

[Mike Sulzer]

You don't really get things to stick to a magnet between the poles.

It sure did last night when I tried it with a ceramic humbucker magnet. Your picture is a bit crude, but it does show that there is a component of the field pointing in or out between the poles.

[Mike Sulzer]

That's the free standing magnet though. Once you attach additional circuitry to either side those lines begin to "have somewhere to go".

But a pickup is an open circuit with the "reluctance" of the air gaps (or actually regions) dominating. The field lines of a free standing magnet can be modified, but not totally changed as in a circuit closed but for a small gap.

[David Schwab]

That's the free standing magnet though. Once you attach additional circuitry to either side those lines begin to "have somewhere to go".

Exactly.

That picture was from Wikipedia for those that are wondering.

I have a questions, how common is it for cast magnets to be un-oriented? That would surely make them sound different.

[David Schwab]

It sure did last night when I tried it with a ceramic humbucker magnet. Your picture is a bit crude, but it does show that there is a component of the field pointing in or out between the poles.

I have an alnico 5 humbucker magnet here. If I lay it on the desk and try to get a piece of 1/8" thick steel to stick right in the middle, between the two poles, it wont. It will however stick between that null point and the edge. It either slides the magnet over, or if I hold the magnet still, moves the steel over. That's holding the steel so the thin dimension is parallel with the poles. If I turn it perpendicular, it will stick because it's bridging the poles.