Why do the various grades of alnico sound different?

[tonedeciple]

Today I tested different grades of alnico bars in neck humbucker to gauge their impact on tone. The grades I tested were A2, 3, 4 and 5. The A2 had a gauss of 776, the A3 measured 584, the A4 measured 838 and the A5 measured 884.

Each magnet produced a unique tone on par with what I've read here and elsewhere on the web. My assumption has been that the different tones were due to the different gauss levels of each magnet. However, the A4 and the A5 I tested had similar gauss levels and yet their tone was very different. The A5, as expected, had a powerful yet very balanced tone, while the A4 was more subdued and much more open.

I had anticipated the difference in tone for the A4 and A5, but since their gauss levels were so similar, I am dumbfounded as to why they would sound so different. Any ideas?

[Possum]

....

The alloy content and mix of each grade is all different. Has little to do with gauss. Here's some homework for you. Google alloy content of alnico or similar such terms and you will eventually find a list of general contents of each grade. But every manufacturer uses a different recipe....

[tonedeciple]

The alloy content and mix of each grade is all different.

I realize the ratio of alloys differs in each grade, but why does this affect tone? Does the composition of each grade alter the magnetic field and thus change the tone? It's not hard to find the alloy mix of different grades of alnico, but I can't find the reason(s) why they affect tone.

[tonedeciple]

I just found the answer in a previous thread here:

http://music-electronics-forum.com/t2693/

Now I think I understand.

[Possum]

...

Its pretty much the same thing as using different alloys of steel, they also are different mixes of chemicals and vary from manufacturer to manufacturer.

[Folkcafe]

Is sintering common with pickup magnets?

And would there be a tonal difference between cast and sintered magnets? It would seem to me that sintering from powders would introduce more impurities (mainly oxides) than casting.

Part of my misspent youth in the mid 80's was working as an R&D tech in the powered metallurgy field. The type of work we did was gas atomization of extremely fine powders. Some materials produced were sub 5-micron. We even worked with neodymium for a brief period. The only thing I recall about that is there were two compositions. The main one we worked on contained lanthanum.

At that time a common method of producing powders for sintering was a plasma method. This introduces even more oxides to the surface of the materials. Also the powder produced was not spherical. The gas methods we were developing melted under vacuum and atomization occured in an controlled chamber in the absence of oxygen. The main goal of most of our research was in producing extremely high quality powders with extremely low contamination. In reading and analyzing these magnet posts, it has left me wondering which has the greatest positive effect on tone, purity of materials or is the magic in the contaminations?

Besides slight variations of chemistry, could methodology of process differences be a bigger factor in the magnets you get from various manufacturers? The two that I am thinking of the most is carbon and various oxides introduced by the methods used to produce the magnets. I remember that even under vacuum, carbon was the biggest problem to regulate in various material compositions. We often used hydrogen (which is a soluble gas) to help purge carbon from the melt. It was really cool watching the molten metal in the crucible froth like soda does when you open the bottle when we would begin to pull a vacuum after introducing the hydrogen.

Then there is MIM (metal injection molding) which sinters under vacuum. This methodology uses metal powders of a calculated packing density with a plastic binding agent and is molded in a plastic injection molding machine. The plastic binding agent is burned off when the "green" molded piece is sintered under vacuum. For precise work and speed, this method has a great deal of advantages over die and sand casting (though requires more technology) Depending on what the answers to the above questions are, I wonder what the results of producing magnets using MIM would result in tone wise.

Just some Sunday morning thinking over a couple of cups of coffee.

[tonedeciple]

Besides slight variations of chemistry, could methodology of process differences be a bigger factor in the magnets you get from various manufacturers?

I think we would be able to answer these questions ourselves if we knew WHY magnet composition affects tone. In other words what's actually happening to the tone when a magnet is change from one composition grade to another.

It easy to state that changing the composition changes different tone, but apparently it's much harder to say exactly why or what's happening to cause this. I've done a little research myself in the last day or so and no one seems to have a concise answer.

[Folkcafe]

The most important thing I learned in my experience in working R&D early in my career was that how the question is asked affects the approach in answering the question. I am a total Noob to building pickups but I come to this question from a uncommon perspective.

From my perspective, there is scientific methodology to determining the "Why?". While impractical for the do-it-yourself group, gas chromatography of an "ideal vintage", known good sounding modern and similar grade undesirable magnet would give you the start to multiple data points that would point to some of these differences. My question stems from multiple references I've read stating that carbon has a pronounced affect in tone (slugs for instance). The aging gray matter between my ears is going to immediately make the same connection to the carbon content in magnets as having similar effect. I am sure someone has done some of this work but one would not expect the results and conclusions of these kinds of tests to be published on, of all places, a public forum.

The genesis of my question really had to do with the impressions I hear about the a large variety of "recipes" in "standard" magnet formulations. At the same time there has been a great deal of discussion regarding carbon and oxides and the effect to tone. Mentally I added the two together and have been digesting it against my experience from 25 years ago. In manufacturing powder the chemical formulation was the easy part. The hardest thing to tightly control was carbon and oxidation in every kind of material I processed.

It occurred to me that if you answer this question for your particular application, then you can specify the correct materials to achieve your desired results. That may require that you end up specifying the chemistry for the magnetic powders including carbon content tolerance and have what you want custom made. Like everything, it only takes money and knowledge.

[tonedeciple]

The most important thing I learned in my experience in working R&D early in my career was that how the question is asked affects the approach in answering the question.

I really understand what you're saying. I really tried to think through the wording of my question in hopes that someone here would read it and think, "Hey, I know what he's after!"

Another way to put it would be along the lines of first explaining how each chemical in an alnico's composition affects the different tonal frequencies. Then, WHY they are doing what they do. Most pickup makers are probably fine with just knowing that increasing or decreasing a particular chemical's % ratio will alter the tone and specifically what frequency they are impacting, but I'd kinda like to know why.

I know the why behind how the coil's design affects tone. Now I want to round out my understanding with same for the magnet(s).

[Folkcafe]

Please don't take my ramblings as any sort of criticism of the clarity of your question. I also apologize for what now seems to be threadjacking.

As being new to this, I've been reading through a great deal of older posts. To my analysis there are just some missing pieces to the puzzle. So I have started to give a lot of thought to all the various aspects involved. So far my instincts tell me there is more to it than the basic metallurgical formulations (why I asked about carbon and oxides). The reason I asked the original question about sintered magnets has to do with material density. I thought this might be another factor. Sintered materials are not as dense as cast unless sinter-forged. Vacuum casting is something else entirely.

So unfortunately I've only added to the question. I'm half expecting to get seriously slapped down as I have made some mental leaps here. I only hope it is read as intended, to be thought provoking because I too would like to be able to make the correlation between magnet composition and tone. Even if I'm never in a position to be able to specify exactly what I want.

[tonedeciple]

Please don't take my ramblings as any sort of criticism of the clarity of your question. I also apologize for what now seems to be threadjacking.

No worries. I didn't take your comments as criticism. But it was hard to convey that I want to go beyond the surface here. And as far as threadjacking, I think it's all related and worthy of discussion. Now we have to dig deeper and see what we can come up with. So far I've read that different magnet formulations can result in changes in eddy currents, changes in inductance and changes in the shape of the magnetic field. It's probably a combination, but knowing exactly what each ingredient does and to what spectrum of the tone might help to take out some of the guess work when designing tone.

[MesaDCLP]

I believe the exact metal content is moot. The reason is because the content actually has an indirect effect on the tone. The metal directly affects gauss and oersted values of the magnet. It is oersteds and gauss that are shaping the magnetic field. Now with different alloys you have different gauss to oersted ratios which accounts for the tonal variances.

For example, measure the gauss of the A4 and A5 again. Pretty close in value, right. Well, now measure the oersted value, and you will see that the two values for each magnet would be different even at the same measured distance. You could use some kind of wooden spacer between the magnet and the meter. Try one then two then more spacers, and you will see how the values are proportional to the same magnet. However the values between the two magnets measured at the same distance are not related at all.

I could be wrong, but this seems to be a pretty scientific way to describe what contributes to a magnet's tonal properties. I'd love to hear other thoughts on this, because it seems the alloy content comes under question a lot when I don't think people are seeing the big picture. In theory, two magnets with the same gauss and oersted values would sound the same regardless of their chemical composition. Of course, the material will affect the operation temperature, but that's not a typical concern in pickups.

[onusx]

mesaDCLP's answer is similar to what i've read from other sources. for example in the london power cab building book, the author claims magnet material doesn't effect tone whatsoever, and that if you had two magnets of the same "strength" in a speaker, they'd sound the same.

that seems like an oversimplification to me, but the concept seems to make sense-- if you had two magnets with identical magnetic properties, of different materials, they'd sound the same...

however, obviously different magnet materials produce magnetic fields in different ways. i don't understand the way magnetic fields are described very well. maybe someone could explain that more clearly, so the descriptions of various magnets' properties would make more sense. i really don't understand the difference between gauss and oerstads, for starters.

the point that often comes up about eddy currents in pickups effecting tone seems somewhat valid, but if i understand it, the differences caused by eddy currents are subtle and hard to describe/measure, compared to other properties.

i'm guessing it's very difficult to articulate the effect on the overall magnetic field of altering the alloy, e.g. tweaking the amount of nickel by a certain percentage. but maybe there are some decent theories out there based on the existing information about the properties of various types of magnets?

the energy required to magnetize/demagnetize ceramic magnets was mentioned, for example. ceramic magnets often sound quicker/crisper to me, with more transients and a little more "edge" or harshness to the sound, and i've heard it suggested that it's because of the magnet's greater sensitivity.

what theories do people have about the role each different magnetic characteristic plays in what frequencies and tones are sampled from a vibrating string? i'm sure i'm not naming them correctly, but how would magnetic pull, strength and density of the magnetic field, and resistance to demagnetization, effect the way the string is sensed? how does the shape of a magnetic field change based on the strength of the magnet? is there a way to visualize the field, and correlate differences to various magnetic compositions (such as "alnico II creates a wider but more permeable field than a5?" i don't know if that's true, but maybe there's a way to "see" the differences and then theorize about the effect on tone? )

i have a hard time understanding hyper-technical, math-based explanations about some of these things, but i think there's also a tendency to get pseudo-scientific about a lot of subjects in luthiery. we can hear the differences, but it seems that scientifically representing some of the reasons we can hear them gets tricky.

[Folkcafe]

I'm trying real hard Ringo

But this magnet stuff is complicated.

One thing I want to make clear, I don't know shite about it. I am grateful for Mesa's message because it has forced me to change directions.

The first thing that needs to be made clear is that I am trying to answer a question that is different from the original poster. I have repeatedly read about sonic differences in magnets of the same size and grade but originating from different sources. This puzzled the hell out of me. My first reaction was it made no sense. Still I have to give the benefit of the doubt to others that are well respected and certainly more knowledgeable than I.

So the question that I am trying to wrap my head around is, how can magnets of the same grade and size, sound different?

Late yesterday I took a total left turn. As a result I've been reading a variety of materials on the subject and while I think my head is going to explode, I have found some very useful clues.

Lets make some clarification to one of my mistakes. The biggest one I've made is to read "recipe" as ingredients. This led me down what I am certain now is the wrong path.

Still as a result of my error I looked into the chemical composition of alnico magnets. I found this.

"The composition is Fe-17% Ni-
13% Co-9.5% Al-6% Cu (wt% ) with the optimum
heat treatment: solution treat at 1250°C for 30 minutes,
cool to 650°C in 4 minutes, temper at 600°C for
4 hours, and slowly cool to 400°C. The resulting magnetic
properties are H, = 400 kAm-', Br = 0.8 T and
BHm,, = 13.5 k ~ m -"

I immediately read "solution treat" and then it dawned on me. Follow this up with reading the statement.

"The magnetic properties of Alnicos 5 and 7 depend
on the decomposition of the alloys into two coherent
b.c.c. phases: a1 (Fe-Co rich) and a2 (Al-Ni rich)
11, 21. The a1 phase is strongly ferromagnetic while
the a2 is weakly or non-ferromagnetic."

While I know a little about this, I am certainly wishing I had paid better attention when I was working under two scientist with Phd's in metallurgy. Honestly, they tried to cram this into my brain.

Having had some experience with processing some alloys, I had some understanding of the need to hold a solution at temperature with some alloys. In the case of alnico alloys, bonding takes place with iron and cobalt and aluminum and nickel and this is the determining factor regarding its magnetic properties. More web reading led to information regarding the effect of quench cooling on alnico magnets. Then tempering. All of these steps affect the magnetic properties of alnico magnets.

As the only magnet material I've worked with personally was neo and the fact that when the argon hit that stream of molten metal, it instantly cooled and there was no need for a quenching process. Bonding and tempering would take place by someone else. I had no reason to know anymore, I had work to get done.

This is getting long and I've still a lot of reading left to get through. Suffice it to say that I've replaced the word "recipe" with "process" as it is mainly the processing of the alnico material that is the variable. You change how you quench or temper it, you will change the magnetic properties of the materials. So in that regard Mesa was sort of right in one regard but wrong for other reasons. Changes in temperature and time are easy variables to assume might happen between vendors.

I am certain there are those on this board who already know much more about this but they have no incentive to spoon feed it to us rookies and I respect that.

My purpose in seeking the answer is because the whole idea of it just nagged at me. The sad part is, at my level, I am just happy to keep building my single coil pickups using the magnets I get from Mojo. I just needed to know that all this talk wasn't similar to the kind of hype they try to sell you with Monster Cables.

I also did find an answer to the question regarding differences in sintered and cast magnets.

[Possum]

.....

You're making this all too complicated. Alnico's main ingredient is IRON. One of the major reasons the content changes the tone is that like any other ferrous metal, eddy currents and inductance from the metal composition are what is most affecting the tone. Look at the chart of composition, alnico 3's main difference from the others is that there is no cobalt. It also holds a much lower charge. I've never tried this before but take you alnico bar magnets and completely deguass them then put each in a humbucker that is kept at exactly the same temperature, and use your Extech LCR meter and write down all the readings for each magnet. Then magnetism is taken out of the equation and you will only get readings of what a chunk of ferrous metal is doing in a circuit. Or alternatively degauss each magnet to an exact measurement so they all read the same. Again you'll mostly be getting its readings based on metal content. For sure every manufacturer is doing different methods. I'm sure each companie's products aren't all the same density. Vintage magnets probably had much more problems with oxygen than now. Its all kind of moot anyway, unless you are having magnets custom made and are an expert in the field, enough to tell them what to change. We've already seen one guy do something the magnet manufacturer advised against and his magnet samples I go lost their charge over several months...