Why do different magnet type produce different sounds?

[Mike Sulzer]

Have you done this test? If so, why not tell us your results. If not, then suggesting that differences might result from changes in the distribution of the magnetic field (if you mean the permanent field) is a bit premature. Adding a steel plate alters the electrical properties of the two coils. That is, the field produced by a test current through the coil (such as used by an inductance meter or a driver coil) is different and thus the inductance changes. The permanent field has no direct role in the changes.

Here is an experiment you can do that will be a learning experience for you and the forum members. Wind a typical 8,000 turn Strat-type pickup with a center tap at 4000 turns. But if you want to monitor each half at the same time you will need to add two additional wire mounting miniature rivets to make a 4000 turn end for the inner coil and then the start winding for the outer coil 4000 turn winding. With these 4 wires you can short the two center connections to place the inner and outer coils in series like a traditional pickup but also measure both the inner coil and outer coil at the same time with and without a ferrous metal plate under the pickup. This way you can see how much stronger the inner turns output level is compared to the outer turns farther away from the magnetic field and then add the ferrous metal plate to redistribute the magnetic field and see what the output level changes are in both the inner and outer coils. I suspect that the inner coil will have a higher output than the outer coil, and when the ferrous metal plate is added to the bottom of the pickup the outer coil will become more efficient. But, let the numbers speak for themselves.

Use a dual trace oscilloscope so you can monitor the output seeing plucked guitar strings rather than a driver coil. Do the test with channel 1 on the inner coil and channel 2 on the outer coil to see instant output levels at the same time. Then, reverse the pickup channels and do the test again to eliminate scope calibration from being an issue with the results. Take measurements with all the open strings, all the strings at the 5th fret, 12th fret and the 17th fret to see how string distance from the pickup poles affects the output in both the inner and outer coil with and without the ferrous metal plate. The beauty of this test is that anyone can replicate it with only a slight modification of a common style pickup to make an independent inner and outer coil with about 4000 turns on each coil. Those wishing to take this test farther can divide the coil into an upper inner and outer coil and a lower inner and outer coil to see the effect of coil distance from the strings with and without a ferrous metal plate.

I hope this helps? Post the results if you do this. This will be very informative.

Joseph J. Rogowski

[Antigua]

[COLOR=#3E3E3E][INDENT]

The differences in permeability and the conductivity (eddy currents) both matter. The permanent magnetic field plays no direct role at all. It is those two properties of the magnetic material make the difference, not the permanent field. The ceramic is almost the same as air for those two properties, as are the rare earth strong magnets. (The permeability of Alnico is a function of the magnetization, and so the permanent field can be a factor through that indirect route.)


...


That is, the field produced by a test current through the coil (such as used by an inductance meter or a driver coil) is different and thus the inductance changes. The permanent field has no direct role in the changes.

That's interesting. Does the permanent magnetic field matter equally as little if an actual guitar string is being used, instead of feeding it current or an alternating electromagnetic field? Does the involvement of a real guitar string change the situation?

[Mike Sulzer]

No, the string does not change much of anything. It is not very much magnetic material and it sits in free space. This also means that the exact permeability of the string is not important for the voltage produced as long as it is ferromagnetic to some degree.

That's interesting. Does the permanent magnetic field matter equally as little if an actual guitar string is being used, instead of feeding it current or an alternating electromagnetic field? Does the involvement of a real guitar string change the situation?

[Antigua]

No, the string does not change much of anything. It is not very much magnetic material and it sits in free space. This also means that the exact permeability of the string is not important for the voltage produced as long as it is ferromagnetic to some degree.

So it's your opinion that the significance of the magnet is entirely / almost entirely in how it effects inductance, or are you holding out that not-yet-known differences might exist elsewhere?

[ADW]

I've been getting frustrated with resources around the web that promise to explain the difference between AlNiCo 2, AlNiCo 3 and AlNiCo 5. They talk about how there are different balances of alloys, that some are magnetically stronger that others, then [magic goes here] and AlNiCo 2 ends up sounding softer, AlNiCo 3 has less string pull, and AlNiCo 5 is brighter and stronger... but none of them say why. I get the feeling none of them really know why since it never gets mentioned in the ten or so webpages I've looked, at and a book I've read all about pickup design. So there's sort of a black hole of information, because if you go the magnet experts, they can't tell you why AlNiCo 2 sounds different than AlNiCo 5 since they don't care about that, they care about it's industrial applications, such as heat tolerance, shock tolerance, coercivity, the ability to change polarity, form custom shapes, etc.

So why exactly does AlNiCo 2 usually sound softer than AlNiCo 5? If it's merely because it's weaker in strength, then why doesn't a degaussed AlNiCo 5 sound like an AlNiCo 2 in a given context? IME, a daguassed AlNiCo 5 actually sounds even brighter than a fully charged one, albeit weaker, but the point being, in the opposite direction of the AlNiCo 2, which confounds the notion that the difference in sound with AlNiCo 2 owes to a weaker field.

Does anyone know what specifically causes the various AlNiCo grades to perform differently, regardless of gauss?

Side question but equally important, apparently in Strat style pickup, with the AlNiCo being in the center of the coil, the magnet material has an impact on inductance since whatever is in the center of the coil will impact how the coil performs, whether it be a magnet, air, or something else, but when you swap magnetic bars on a humbucker, there's only ever steel in the coil's core, that doesn't change. Does this mean that swapping magnets on a humbucker will have no consequence on the inductance and Q factor, where as swapping magnets in Strat pickup it would?

a little late to this, but after speaking with one of our phd's (we make magnets for particle accelerators and high energy physics experiments) apparently the "mu" of alnico decreases as the grade increases. alnico 2 having the highest mu and alnico 8 having the lowest. the theory is that at the pole using alnico 2, the field that the string sees looks like a gradual bell curve. using say alnico 8, the curve is not actually a curve but more of a sharp edged bump -flat across the top with sharp edges. as the string moves through this field, you can imagine what the different profiles will to do to influence the oscillation of the string. chamfers applied to the poles of numerically higher grades of alnico will soften the curve. this applies to pickups using direct poles made of alnico (strat type). i didn't ask about humbuckers i'm afraid.

[Jazz P Bass]

(we make magnets for particle accelerators and high energy physics experiments)

Cool!

[Jazz P Bass]

(we make magnets for particle accelerators and high energy physics experiments)

Cool!

[somebodyelseuk]

Hiya,
New to this forum, new to messing with pickups, and it seems kinda karnic somehow that my first post is in a thread by someone called 'Antigua' - my first Strat was a 79 in 'antigua' finish.

Anyhoo, getting back on topic, I've been scratching my head over this magnet lark for a while. I've found the same to be true as the OP regarding different Gauss strengths of AlNiCo V magnets in a Fender pickup versus sound produced., ie. no difference other than the output level varying by a couple of decibels.
Being a plastic molded bobbin, I bought some AlNiCo III poles and swapped them in - so NO variables, as we all know how coils are not identical even on mass produced pickups, right? All my dabbling has involved only using one pickup from the set, no controls, no soldering, no amps, DId into a computer/DAW, via a Mackie VLZ mixer to take the HiZ signal to line level and no alteration of any EQ.level knobs after the initial level was set for the 'experiment'. After recording, I used the DAW's spectrum analyser to compare the waves and see if my ears were missing something. In every case I 'played' a first position E chord, using a single downstroke across the position of the middle pickup rout.
The difference in 'tone' was only really of any significance when the pickup was placed in the bridge position. Middle position, debateable. Neck position, no difference whatsoever.

Haven't experimented with humbuckers, yet, but if I've drawn any conclusions, so far, it's that (as usual) guitarists tend to exaggerate and most differences can be compensated for by turning the knobs on the amp.
Seriously though, the comment about the shape of the magnetic field being different kinda makes sense, as it occurred to me that the A3 in bridge had a 'almost humbucker character' to it - the closer to the neck pickup position on an open string, I would think the footprint of the field would be less... the vibrating string... well, I can picture what's going on, but I'm struggling to put it in to words...
Regarding the bar magnets, when used in a humbucker, you're effectively creating a 'horseshoe' shaped magnet. Granted the poles are usually steel, but they carry the field and so they will deform it, n'est ce pas?

[salvarsan]

apparently the "mu" of alnico decreases as the grade increases. alnico 2 having the highest mu and alnico 8 having the lowest.

Needs elaboration.

<fool "style=pedantic">

The magnet alloy's Mu or
relative permeability affects the coil inductance
which affects the bass-treble balance.

Higher mu -> more inductance -> more bass

Stronger magnets have lower mu -> more treble.

the theory is that at the pole using alnico 2, the field that the string sees looks like a gradual bell curve. using say alnico 8, the curve is not actually a curve but more of a sharp edged bump -flat across the top with sharp edges. as the string moves through this field, you can imagine what the different profiles will to do to influence the oscillation of the string. chamfers applied to the poles of numerically higher grades of alnico will soften the curve. this applies to pickups using direct poles made of alnico (strat type).

The remanent field gradient affects the amplitude envelope from the plucked string. Some musicians lower the pickups as far as possible to prolong the fast note decay that is characteristic of 25.5" scale guitars.

-drh

[fieldwrangler]

Salversan wrote:

Some musicians lower the pickups as far as possible to prolong the fast note decay that is characteristic of 25.5" scale guitars.



My general sense of this has tended towards an opposite view. To me, the whole A-D-S-R progression feels elongated with longer scale lengths when the neck to body coupling is equivalent. Of course, when you're trying to make "all other things be equal" do you pick string tension, string diameter or string-length-to-diameter metrics for "equivalence?"

Bob Palmieri