Is it possible to accurately describe the tone of magnets and/or pickups?

[Helmholtz]

I do not understand this. I think that the Alumitone is just a single turn pickup with a very high step up ratio.

Yes and this very low resistance single turn in the Alumitone is shorted and hence constitutes a perfect eddy current loop. Consequently sustain will suffer if the magnetic flux is strong enough.
It looks like a potent eddy current brake.

[Helmholtz]

Won't the impedance of the circuit that the pickup is attached to affect the string's sustain.

Yes, I already mentioned this. The higher the PU current the stronger the damping effect.

[Helmholtz]

A dead short in the coil would quickly stop the string due to eddy currents in the coil

I have some doubts, as even the short-circuit current a PU can produce is very, very small. It is limited by the DCR anyway.

but what if you turn the volume way down to where most of the signal is shunted to ground?

If the volume pot is wired as a variable voltage divider (as usual), the PU always "sees" the full pot's resistance.

[Helmholtz]

In his book, Zollner shows the results of an experiment with an A5 magnet fixed in 2,5mm= 0.1" distance from the vibrating string over the neck PU position. The signal level difference caused by the presence of the magnet was around 1dB after 5 seconds.
His explanation for the small, magnet raised damping is increased hysteresis losses in the string. I consider this another plausible possibility.

He also showed that the damping caused by the player's hand-to-neck contact is much stronger than the damping caused by the magnet at realistic distances (i.e. avoiding that the vibrating string touches the magnet).

[bbsailor]

I do not understand this. I think that the Alumitone is just a single turn pickup with a very high step up ratio.

Mike is correct about this but there is more!!!

There is another characteristic of this high turns ratio current transformer where the thick primary aluminum frame acts as a single turn string loop. It is "skin depth", something not normally discussed in relation to guitar pickups. See this chart to see skin depth of copper solid wire at various gauges. http://www.powerstream.com/Wire_Size.htm.

Note that AWG 8 is .1285" diameter and only passes full current to the wire core up to 1650Hz. This frequency goes slightly higher than the maximum guitar primary frequency at the high e string at the 24th fret at about 1448 Hz. However, upper harmonics would be affected more. Lace uses the skin effect in the aluminum frame as well as the turns ratio in the transformer coupling to affect the sound quality and output voltage level of the Alumitone pickup design. A small bundle of AWG 12 .0808" diameter wire strands for the string loop would take the frequency up to 4150Hz, typical of traditional guitar pickups and amplifier speakers. A larger bundle of AWG 18 at .0403" diameter strands would need to be used to get up to 17Khz. The actual science of this is known for radio transmissions and Litz wire but the application of this for guitar pickups is totally "in the ear of the beholder". I find that strand size and skin depth is more appropriate for use in acoustic guitar pickups where you do not want the typical "electric guitar sound" with the resonant point in the same area where the human ear is most sensitive. Since current in the primary string loop is now dependent on string and harmonics frequencies and skin effect, how much current at different frequencies can be generated and converted by the turns ratio can act as sort of an audio filter.

Joseph J. Rogowski

[ken]

but what if you turn the volume way down to where most of the signal is shunted to ground?
If the volume pot is wired as a variable voltage divider (as usual), the PU always "sees" the full pot's resistance.

This is true, as *only the signal* would be attenuated by the pot slider. The total resistance of the pot would always be across the pickup.
Now would the pickup react differently if the volume pot itself was changed... say from 250K to 1M resistance?

As for what happens if you hardmount a pickup to a guitar instead of using springs or rubber tubing, EVH screwed his pickups right down to his guitar body with woodscrews.

Ken

[Mike Sulzer]

Yes and this very low resistance single turn in the Alumitone is shorted and hence constitutes a perfect eddy current loop. Consequently sustain will suffer if the magnetic flux is strong enough.
It looks like a potent eddy current brake.

It is a single turn pickup operating into a transformer with a single turn primary, a transformer that steps up the impedance something like 10^8 times. I think that the current flowing in that single turn is effectively nearly the same as that of a many turn pickup.

[Mike Sulzer]

Yesser. I actually DO get that. But pickup mounting systems aren't all THAT secure really. Surely there is SOME movement. I admit I never thought about it before Helmholtz mentioned it. I just don't think it makes sense to ignore it. After all, we do strive for that extra five percent on this forum. If all we wanted to do was play our guitars we could ignore a lot of what's discussed here.

I agree! But is it 5% or .01%?

[Mike Sulzer]

Yes, string bending involved in the vibration means material deformation. Though mostly elastic (non-dissipative), there is also has a lossy component in non-ideal materials. As higher harmonics bend the strings at a higher rate, they lose energy faster.
I just don't see neither a higher bending rate nor a higher bending amplitude in the presence of a magnetic force. The field just minimally shifts the equilibrium or rest position of the string in the plane perpendicular to the fingerboard.

The slightly different frequencies of up-and-down vs. sideways vibration caused by a strong magnetic field produce a beating effect as seen in the waviness of the signal decay. A local minimum in the decay means that the energy content in the up-and down vibration has momentarily decreased while the energy in the horizontal motion has correspondingly increased. This energy exchange repeats at the beat frequency. I can't think of a reason for increased losses produced in the energy exchange between the two vibrational modes. If the amplitude (and thus the bending) of one mode increases, the amplitude of the other one decreases.

Did I adress what you meant?

Put a strong magnet near a string and shine a light on it. When I do that, I see a different effect than without a magnet.This dies away very quickly, and so you have to watch carefully.

Are you sure you can pump energy between different modes with different, but close, frequencies without a loss mechanism to conserve momentum? (I do not know the answer to this, have not done the physics, but it looks like it might be something that needs some thought.)

[Helmholtz]

I am not aware of such additional loss processes. Momentum is no energy category and momentum inversion does not consume energy. But I am no acoustics expert like Zollner and cannot exclude other minor loss processes. I am quite sure though, Zollner would have mentioned them if they were relevant.

[Antigua]

Yes, string bending involved in the vibration means material deformation. Though mostly elastic (non-dissipative), there is also has a lossy component in non-ideal materials. As higher harmonics bend the strings at a higher rate, they lose energy faster.

The way I understand it, having read some papers about acoustic guitar physics, is that the higher harmonics divide the string into smaller segments, and that those smaller segments are more mechanically rigid than are longer segments, and higher rigidity, or less elasticity whatever, means more energy lost in the form of heat within the guitar string. Supposedly this relates to why flat wound strings produce less treble; the flat interlocked winding is more rigid that round wound windings.

So it's a given that higher harmonics decay faster, I think we can all agree that any change that shifts energy to higher harmonic levels will therefore result in a net loss of sustain. IIRC, in my own testing I found that putting the magnetic closer to the bridge (or the nut) promoted a transfer of energy to higher harmonics than if you place the magnet over the middle of the string, for much the same reason that if you pluck the strings by the bridge, you also get higher harmonics. Therefore it might be that increased magnetic pull at the bridge could reduce sustain more than magnetic pull elsewhere, by shifting the energy into higher harmonic levels that experience greater mechanical damping within the guitar strong.

[Antigua]

Yesser. I actually DO get that. But pickup mounting systems aren't all THAT secure really. Surely there is SOME movement. I admit I never thought about it before Helmholtz mentioned it. I just don't think it makes sense to ignore it. After all, we do strive for that extra five percent on this forum. If all we wanted to do was play our guitars we could ignore a lot of what's discussed here.

As for what happens if you hardmount a pickup to a guitar instead of using springs or rubber tubing, EVH screwed his pickups right down to his guitar body with woodscrews.

I think it makes sense to ignore it in this case, because even the rough math, which is to consider the small magnetic coupling, and the tremendous difference in mass, means that this effect will not be in the %5 range, nor the 0.01% range, but somewhere even below that. The difference between mounting rings versus body mount is equivalent to pissing in the ocean and expecting the sea level to rise

Won't the impedance of the circuit that the pickup is attached to affect the string's sustain. A dead short in the coil would quickly stop the string due to eddy currents in the coil, I'm not sure if a 50k ohm load would have any effect but what if you turn the volume way down to where most of the signal is shunted to ground?.

The guitar string produces some magnetomotive force, and that force is like a potential voltage, and what stops that voltage from being fully realized is magnetic reluctance between the magnemotive force and the loop(s) of wire where the measurement is made. The magnetomotive force must be rather high, because we know the reluctance also very high (lots of air gap between the string and the pickup), and yet a guitar pickup produces a usable signal. Knowing that the reluctance path is very high, it can also be said that eddy current action between the string and pickup will be very low by the same virtue. I bet if someone could calculate the value of the reluctance path, or the magnetomotive force, then they could probably also figure out the counter electromotive force, which would give some clue as to how able the pickup is to decrease sustain. With a typical eddy current brake, the reluctance path between the magnet and the conductor being brought to a halt is usually small, by comparison.

[bbsailor]

I think it makes sense to ignore it in this case, because even the rough math, which is to consider the small magnetic coupling, and the tremendous difference in mass, means that this effect will not be in the %5 range, nor the 0.01% range, but somewhere even below that. The difference between mounting rings versus body mount is equivalent to pissing in the ocean and expecting the sea level to rise




The guitar string produces some magnetomotive force, and that force is like a potential voltage, and what stops that voltage from being fully realized is magnetic reluctance between the magnemotive force and the loop(s) of wire where the measurement is made. The magnetomotive force must be rather high, because we know the reluctance also very high (lots of air gap between the string and the pickup), and yet a guitar pickup produces a usable signal. Knowing that the reluctance path is very high, it can also be said that eddy current action between the string and pickup will be very low by the same virtue. I bet if someone could calculate the value of the reluctance path, or the magnetomotive force, then they could probably also figure out the counter electromotive force, which would give some clue as to how able the pickup is to decrease sustain. With a typical eddy current brake, the reluctance path between the magnet and the conductor being brought to a halt is usually small, by comparison.

Antigua,

Here is a quick way to measure any eddy current attempting to suppress a vibrating string in a magnetic field.

First, establish a baseline with the magnet near the string with a controlled pluck timed till it fully decays.
Now, obtain a piece of copper wire that has 10 to 15 times less resistance than the test string. Find a low resistance way to secure this wire across the string, attached behind the nut and bridge to short out the string. Pluck the same string in a controlled way and measure the time for this string to fully decay.

The shorted string will induce more current in the string wire while vibrating in the magnetic field. Since the coupling between the string and magnet is relatively low there will be some measureable decay in time. The variables will be the area of your chosen string, the strength, length and closeness of the magnet to the string and the lowest resistance connection to short out the string.

Based on my experimentation, a vibrating string will induce a voltage in itself depending on the length of the magnetic field. It can range from about 1mv to about 3 mv. Then, when you put a 8 ohm transformer across the string and use the high impedance side such as 10K to 50K side connected to the amp input, you will hear an output in the passive pickup range. This is how the Stringamp for the violin works.

Joseph J. Rogowski

[Helmholtz]

It is a single turn pickup operating into a transformer with a single turn primary, a transformer that steps up the impedance something like 10^8 times. I think that the current flowing in that single turn is effectively nearly the same as that of a many turn pickup.

I disagree. The primary current is determined by the loop EMF, the loop resistance and the loop inductance. This primary current is the magnetizing current of the transformer.
Secondary signal current stepped up with the (inverse) turns ratio of around 10000 will further increase the primary current as with any transformer. Secondary current cannot decrease primary/magnetizing current.

[Helmholtz]

Higher harmonics decay faster, true.

Do you have positive evidence that the same PU at the same distance from the string produces stronger string damping at the bridge position than at the neck position?

Do you have positive evidence that stronger fields/closer PU distances increase the amplitudes of the higher harmonic relative to the fundamental?