Why do different magnet type produce different sounds?

[Leo_Gnardo]

double post how'd that happen?

[Antigua]

At a guess, it may be something to do with the shape of the field, with the aim of optimising the filed in the voice coil gap.
So maybe different alnicos have differing field shapes?

When a magnetic field is made wider by way of ferromagnetic pieces, like the baseplate on a Tele bridge, the voicing changes somewhat since a wider portion of the string is influencing the the coil(s), but the difference between AlNiCo 2 and ALNiCo 5 tends not to involve the voicing so much as the amount of high end that is produced and the pick attack characteristics, or at least is this is perceived to be the cased by a large number of pickup winders and guitarists. I think there could be a difference in the nature of the magnetic field that is produced, but I think it's shape is going to be to mostly or entirely the same.

[freefrog]

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?

Here are the measurements that I've recently done on a pair of P.A.F. clones with various rough cast alnico bar magnets bought (already magnetized) to AddictionFX:

A3: 4.42H / 3.73H

A2 :4.37H / 3.69H

A4 :4.27H / 3.65H

UO A5 :4.22H / 3.56H

Short A5 : 4.14H / 3.51H

The magnetic fields measured on these mags with our lab teslameter was almost twice higher with the U0A5 (stronger charge) than with the A3 (weaker charge).

FWIW.

[jack briggs]

Here are the measurements that I've recently done on a pair of P.A.F. clones with various rough cast alnico bar magnets bought (already magnetized) to AddictionFX:

A3: 4.42H / 3.73H

A2 :4.37H / 3.69H

A4 :4.27H / 3.65H

UO A5 :4.22H / 3.56H

Short A5 : 4.14H / 3.51H

The magnetic fields measured on these mags with our lab teslameter was almost twice higher with the U0A5 (stronger charge) than with the A3 (weaker charge).

FWIW.

This is commensurate with my tests. The alnico grades that are generally accepted as "weaker" grades (having lowest BH or maximum energy) show the highest inductance because of higher iron content. Any other iron in the magnetic core such as pole pieces, keepers, etc. will affect the induction readings as well. A screwdriver on the bobbin mounting screw underneath the magnetic core will affect the measured inductance.

Keep it coming.......

[Antigua]

Here are the measurements that I've recently done on a pair of P.A.F. clones with various rough cast alnico bar magnets bought (already magnetized) to AddictionFX:

A3: 4.42H / 3.73H

A2 :4.37H / 3.69H

A4 :4.27H / 3.65H

UO A5 :4.22H / 3.56H

Short A5 : 4.14H / 3.51H

The magnetic fields measured on these mags with our lab teslameter was almost twice higher with the U0A5 (stronger charge) than with the A3 (weaker charge).

FWIW.

Were these measured with an LCR meter, or through some other means?

With variations that close, I'd think a margin for error would become important, and I wonder what it would be in the case. Factors would be the quality/purity of the alloy as well as it's consistency end to end. My own test have shown them all to be really close in numerous respects also, and that's disheartening because I don't have the time to collect numerous examples from numerous foundries in order to establish more concrete trends.

[Johnnie5]

Hello, Lots of great info here. I don't quite understand the initial question, most of it seems to be over my pay grade. I can tell you that in mt experience that I noticed the resonant peak of the pickup is more pronounced the higher the grade of magnet. I scoped most of the pickups we make at Nordstrand to get some objective data and I found that AlNiCoIII, IV, and II have lower resonant peaks (about 15db) and lower output by about 5db. They do not sound quieter though. That being said, we all agreed in the shop that a3 sounds more lush and dynamic while neo sounds clinical (both compared against a5). The harmonics that are not generally pronounced are more apparent when the resonant peak is lower and I think that's the main subjective difference. You are hearing more of everything. Like a compressor that doesn't pump and breathe.
I hope this helped someone out there...

Article I wrote on magnets: http://nordstrandpickups.com/alnico-and-numbers/

[Mark Bracewell]

Thanks Antigua, for the incisive questions.

You mentioned "we've ruled out inductance since it's external to the coil"... are you sure that's the case?

Inductance seems to be a likely culprit to me. And does not the tele base plate add fodder to that idea?

Sadly, like everyone else, I don't know the answer :/

[freefrog]

Were these measured with an LCR meter, or through some other means?

Yes, it has been measured with an LRC meter.

With variations that close, I'd think a margin for error would become important, and I wonder what it would be in the case. Factors would be the quality/purity of the alloy as well as it's consistency end to end. My own test have shown them all to be really close in numerous respects also, and that's disheartening because I don't have the time to collect numerous examples from numerous foundries in order to establish more concrete trends.

I've posted my previous answer while I was busy (in such a way that my sentences aren't even gramatically correct; sorry about that). Let's complete it.

Personally, I don't find my last results surprising when I compare them to previous measurements done here since 2003: I've consistently noticed a close relationship between alnico grade and measured inductance once the bar magnet is in the pickup, with smooth or rough cast bar magnets of various origins (I've tested vintage mags too).

I lack of time to dig my archives but here is another example that I've here right now. It's about another boutique P.A.F. clone, bridge position:

With stock magnet (supposed to be a long A2 bar of unknown origin): 5.67H.
With a smooth A2 bar borrowed to a Duncan Seth Lover: 5,6H
With a short A2 mag (if memory serves me): 5.4H
With a vintage A5 mag: 5.27H
With an AddictionFX UOA5: 5.3H

And so on.

Once again, FWIW (= "my two cents").

[Antigua]

You mentioned "we've ruled out inductance since it's external to the coil"... are you sure that's the case?

I'm not entirely sure, but the reasons I have for doubting that as a major cause is that people say the AlNiCo 2 tends to do X, and the AlNiCo 5 tends to do Y (3 and 4 seem to be more of a moving target), and I mostly agree with conclusions X and Y, and it doesn't seem to me that the differences described directly correlate with changes in inductance, for example, more or fewer or winds on the coil doesn't seem to have the same effect as choosing between the different AlNiCos.

Also, I once did a test of my own, I measured the resonant peak of a pickup using an inducing driver coil rather actual guitar strings or an LCR meter, and then stuck some neodymium magnets to the underside of the pickups and measured it again, and there was no change in the resonant peak. This also also gets me to thinking that the difference is in the way magnet allows the string to relate to the coil, not in any effect the magnet has on the coil's electronic properties. I'll redo this experiment tonight with AlNiCo bars, at the time I had neodymiums on hand, but not various AlNiCo bars.

Inductance seems to be a likely culprit to me. And does not the tele base plate add fodder to that idea?

Again, I think the fact that it re-shapes the flux lines is very significant in that case. It's causing the coil to see something different, even if the coil stays exactly the same from an electronic standpoint.

Also I have the Extech 380193, so I'll get inductance measures as well.

[Mark Bracewell]

There's a fascinating old thread here...

One of the messages from Rick Turner is particularly thought provoking, he had mentioned that a driver such as you tested with wasn't the whole picture, as it isn't a string. He seems to suggest that the shape (for lack of a better term) of the field from different magnets may affect the way the string vibrates, thus making some difference. Here's the message, the whole thread is interesting..

http://music-electronics-forum.com/t23027-2/#post194322

[Antigua]

One of the messages from Rick Turner is particularly thought provoking, he had mentioned that a driver such as you tested with wasn't the whole picture, as it isn't a string.

That's definitely true, a driver coil is nothing like a string, but that's also it's advantage, it eliminates the string factor and presents a constant influence, so if the driver coil says two things are the same but am actual string says they're different, then to some extent you can blame the string for the difference.

He seems to suggest that the shape (for lack of a better term) of the field from different magnets may affect the way the string vibrates, thus making some difference. Here's the message, the whole thread is interesting..

That's an appealing theory, but if that's the case, I'm surprised there's not mention about field shape when the topic of AlNiCo grades comes up, not only in the guitar context, but in industrial contexts as well, where they talk about heat and shock tolerances among other things, but do not mention differences in field shape.

[bbsailor]

That's definitely true, a driver coil is nothing like a string, but that's also it's advantage, it eliminates the string factor and presents a constant influence, so if the driver coil says two things are the same but am actual string says they're different, then to some extent you can blame the string for the difference.



That's an appealing theory, but if that's the case, I'm surprised there's not mention about field shape when the topic of AlNiCo grades comes up, not only in the guitar context, but in industrial contexts as well, where they talk about heat and shock tolerances among other things, but do not mention differences in field shape.

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

[freefrog]

I'm surprised there's not mention about field shape when the topic of AlNiCo grades comes up

Malcolm Moore has worked on this subject in 2003 if memory serves me. Not sure the related webpage is still downloadable but if someone wants it, I think to have kept this test in a .pdf somewhere in my archives... PM me if necessary.

Oh, and when I test a pickup with a driver coil and various mags, I don't notice either a different resonant peak. But once the pickup is played, the charge of the magnet and the pickup inductance can almost be "read" in the frequency response obtained.

Granted, it dosn't lead a degaussed A5 to "sound" like an A2. There's probably many things to say about BH curves and what I'll sum up as a "sag" effect... I let this question to real specialists. :-)

EDIT - My bad, it's not Malcolm Moore who has worked on the question mentioned above. I was thinking to this page: Magnetic fields in pickups

[Antigua]

You mentioned "we've ruled out inductance since it's external to the coil"... are you sure that's the case?

Inductance seems to be a likely culprit to me.

OK, I stand corrected, the differing magnets definitely altered the inductance and moved the resonant peak.

I did both an inductance test with the Extech 380193 and a frequency response analysis with a Syscomp CGR-101, and test against AlNiCo 2, roughcast AlNiCo 2, AlNiCo 5, roughcast AlNiCo 5, ceramic 8 and then without any magnet.

First, here's the inductance numbers at 1kHz. My numbers where a bit higher than freefrog's, maybe his PAF had less winds than this Seymour Duncan pickup.

AlNiCo 5: 4.636 H
AlNiCo 5 roughcast: 4.625 H

AlNiCo 2: 4.764 H
AlNiCo 2 roughcast: 4.772 H

Ceramic 8: 4.388 H
No magnet: 4.403 H

I'm surprised by a few things. A) the smooth and roughcast AlNiCo 2 and AlNiCo 5 are amazingly close even though I received them from different magnet suppliers. You hear about dodgy magnet sourcing and variability in alloy formulations, and yet the samples are within .01 H of each other. That's nuts. Surprise B) Ceramic is close in terms of inductance to having no magnet at all. Note that AlNiCo 2 was higher inductance than AlNiCo 5.

~~~~~~~~~

Now here's the frequency analysis with the driver coil, and it largely mirrors the inductance differences.

The topmost red curve is AlNiCo 2, it has the most amplitude ahead of the peak, and it's peak is a slightly lower frequency than the others.

Next down is AlNiCo 5 and AlNiCo 5 roughcast, both are essentially identical overlapping lines. The fact that one is smooth and the other is not apparently makes no difference, probably to the surprise of no one. I had measured AlNiCo 2 roughcast also, but I had made a mistake in the screen shot, didn't want to set it all up again, but it basically overlapped the AlNiCo 2 curve just like the AlNiCo 5's did.

Lastly the ceramic 8 and the reading with no magnet are essentially identical, just as they were in the inductance readings, and also have the highest peak frequency. And don't worry, that's a plenty powerful magnet reading 1300 gauss along the top edge, it's not a dud.

I'm guessing the key difference here is that the AlNiCo's produce eddy currents whereas the ceramic and air don't, and that it's the eddy currents which are to blame for these difference, and that AlNiCo 2 produces more eddy currents than AlNiCo 5... is this correct?



Here's some pics of the test equipment:

[Mike Sulzer]

Surprise B) Ceramic is close in terms of inductance to having no magnet at all. Note that AlNiCo 2 was higher inductance than AlNiCo 5.

~~~~~~~~~

Now here's the frequency analysis with the driver coil, and it largely mirrors the inductance differences.
Lastly the ceramic 8 and the reading with no magnet are essentially identical, just as they were in the inductance readings, and also have the highest peak frequency. And don't worry, that's a plenty powerful magnet reading 1300 gauss along the top edge, it's not a dud.

I'm guessing the key difference here is that the AlNiCo's produce eddy currents whereas the ceramic and air don't, and that it's the eddy currents which are to blame for these difference, and that AlNiCo 2 produces more eddy currents than AlNiCo 5... is this correct?

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.)

Edit: And I forgot to say that in the case of Alnico, it is the changes in permeability that are the dominant effect. The conductivity of Alnico is much lower than steel, and you would not expect much effect from eddy currents. (Tests with rod Alnico magnets versus steel slugs verify this.)