How do the metals in Alnico affect tone?

[kevinT]

I know that each grade of alnico has a different effect on tone. However, what i am unclear about is how do the metals in the bar magnet affect the current that is induced in the coil making a pickup sound the way that it does.

another way to put it....A magnetic field is a magnetic field whether it is A2 or A8 magnetic field ...right? (I'm not considering gauss here) How do the percentages of metal alloys of an A2 and the alloys of an A8 translate into the tone.

For me there is a disconnect in how the metal in the mags physically flavor/alter the tone.

Does it flavor the current in the coil a certain way.

Can anyone explain this in layperson's terms?

[David King]

I heard a talk with the head pickup designer from Guild in 1988 and he swore up and down that the way the current is induced in a pickup is the subtle demagnetization and re-magnetization of the magnet by the string passing back and forth over it. He claimed that this is why Alnicos were better than ceramics, they had a lower coercive threshold and were more easily affected by the string. I have nothing to back this theory up but it's a theory we could probably test out. It certainly doesn't explain why samarium -cobalt and neodymium powered pickup work as well as they do. (when I asked him about the feasibility of using rare earth magnets in pickups he said they wouldn't work well but I doubt he'd even tried them at that point.)

[black_labb]

aside from the gauss, i would say it is inductance. inductance changes the frequency response in the coil. when different materials are put in the middle of a coil the inductance changes. i think more inductance will create a bit of a high end roll off, but could be more complicated than that.

in very simple terms, inductance is a coils resistance to change (ie ac). inductors are used to smooth out voltage ripple in amplifiers to clean up the dc.

someone with more knowledge will probably chime in.

the resistance of the alnico grade may effect it as well (eddy currecnts maybe?)

[soundmasterg]

I will say that my RIC humbuckers that use samarium cobalt magnets have a bright top end with lots of power, and the highs can be somewhat harsh. I use flatwound strings on this guitar to tame the highs down a bit.

Greg

[David Schwab]

I heard a talk with the head pickup designer from Guild in 1988 and he swore up and down that the way the current is induced in a pickup is the subtle demagnetization and re-magnetization of the magnet by the string passing back and forth over it. He claimed that this is why Alnicos were better than ceramics, they had a lower coercive threshold and were more easily affected by the string. I have nothing to back this theory up but it's a theory we could probably test out. It certainly doesn't explain why samarium -cobalt and neodymium powered pickup work as well as they do. (when I asked him about the feasibility of using rare earth magnets in pickups he said they wouldn't work well but I doubt he'd even tried them at that point.)

Current is induced by what is called "variable reluctance".

The idea is when ever a magnetic field is moved by a conductor, current flows. And conversely when you flow current down a wire, it produces a magnetic field, as long as the wire has resistance. Electric fields and magnetic fields are considered two parts of the same phenomenon.

I think some magnets have a "softer" field, and that changes the tone.

[chevalij]

I'm with KevinT. I dont' get it. To me, the only thing that makes sense it the gauss of the magnet. Stronger field, stronger signal. How the hell can the amount of cobalt affect tone. It's magic I tell ya. Abigal was a witch, or a duck, I can't remember which one but she floated!

[Mike Sulzer]

David and Black_labb mention two aspects of the same thing: most ferromagnetic materials respond to applied magnetic fields and amplify them. The degree to which they do this is called the permeability. So the pickup cores do in general amplify the small fluctuating field from the vibrating string. And the core amplifies the field from currents flowing in the coil, increasing the inductance.

But rare earth magnets do not do this significantly; their fields are mostly frozen in, which means they have low permeability. But when used as pickup cores, their very powerful fields magnetize the strings strongly and so they can give high output even though the permeability is low. The high field can make a guitar string sound harsh since its vibration is affected. Heavy strings with high tension should be less affected, but David would know more about that.

[David King]

Hey Mike! What the hell is a nice person like you doing in a place like this? Welcome.

So to summarize, "hard" (low permeability) mags like Ndym and SmCo and C8 are good for bass but not so good for guitar while "soft" (high permeability) magnets like A2 and A3 are better for high strings to the average human ear?

[Possum]

...its not just gauss....

how magnets "sound" is not just gauss. You can have an alnico 4 magnet and an alnico 2 magnet hitting exact same charges and they are not going to sound the same. Inductance for sure is a prime thing that affects tone but I don't think you're going to find a critical analytical list of how each element is going to affect tone. Some elements affect coerciviity and permeability so the more of that stuff in there its going to change how the sound signal sounds. The amount of iron is key also as this is related to inductance. I'm starting to learn more about this stuff because I'm trying to figure out magnetic alloys that are out there. Same stuff as used in magnets. Really, all you can do is use each alloy and listen what it does to bass, midrange, and treble and dynamics. I suppose you could try to quantify that somehow but some thing can't be quantified I guess.....

[Mike Sulzer]

Hey Mike! What the hell is a nice person like you doing in a place like this? Welcome.

So to summarize, "hard" (low permeability) mags like Ndym and SmCo and C8 are good for bass but not so good for guitar while "soft" (high permeability) magnets like A2 and A3 are better for high strings to the average human ear?

Hi David; I have lurked around here for a few months, but took some time off from posting anywhere after I got booted off mimf. (Hello to David Schwab, too!)

Yes, I agree. If you are using just the magnets and want reasonably high output, you have be careful of excessive string pull with neo and SMCO with guitar strings. On the other hand, if you do not need such high output, you can avoid the string pull by using smaller magnets, or moving them down in the coil. I think the rare earth magnets are most convenient when you are using cores made from some non-permanent magnetic material. They allow you to adjust the inductance (and thus the resonant frequency) independently of the magnetic field strength. The rare earth mags do not affect the inductance, so you can optimize the field strength by adjusting the size of the magnets on the bottoms of the pole pieces (or on top if you use really small magnets) without changing the resonant frequency.

On the other hand, I really like pickups with alnico pole pieces. Some time I want to make a pickup like described above, with both the field strength and resonant frequency exactly matching, for example, a tele lead pickup and then compare them.

[David Schwab]

But rare earth magnets do not do this significantly; their fields are mostly frozen in, which means they have low permeability. But when used as pickup cores, their very powerful fields magnetize the strings strongly and so they can give high output even though the permeability is low. The high field can make a guitar string sound harsh since its vibration is affected. Heavy strings with high tension should be less affected, but David would know more about that.

Hi Mike!

I haven't tried them with guitar yet, but I use steel cores in my coils most of the time anyway.

I was able to try a few pickups out swapping between ceramic 8, alnico V and N42 neodymium magnets. It was interesting hearing the tonal changes with each magnet. Using the ceramic as a baseline, alnico is darker and spongier, while the neo has more texture in the mids and highs... a sort of snarly tone.

[SK66]

I believe the two main factors are Gauss and Permeability.
Both are determined by the magnet's material composition and method of creation. Gauss is gauss and has it's effect which I think has been fairly well explained.
However, as Possum noted, two magnets with the same gauss may have different tonal characteristics.
Think of a higher permeability magnet as a "more efficient" magnet. Because it is more efficient at transmitting its magnetic field, it is also more efficient in "recirculating" it's magnetic field to the opposite pole. The resulting magnetic field will have a narrower aperature making it more "focused/brighter" sounding.

[David Schwab]

That fits right into what I hear with the various magnets I've tried.

[Possum]

permeabbility (and coercivity?)

Are there specs or charts that show this? The same thing applies to magnetic alloys and metals, I haven't seen anything on this comparing alnico grades, that would be something to see if it exists somewhere.....

[David King]

http://www.grouparnold.com/products/...ties_2-3-4.htm
http://www.grouparnold.com/products/...ties_5-800.htm
http://www.grouparnold.com/products/...erties_8-9.htm
http://www.magnetapplications.com/USA/alnico.htm