Horseshoe pickups: what do they do that's "different"?

[Mark Hammer]

So yesterday I picked up the latest CD from Blake Mills. Absolute monster slide player, in the same league as Derek Trucks and Ry Cooder, yet able to play jazz progressions like Bill Frizell and mariachi music like David Hidalgo.

A number of the Youtube demos and live things I see from him have him playing a Strat-en-stein with a gold foil in the neck position and a horseshoe derivative at the bridge. Not split like a horseshoe, but the strings pass through it, rather than over it.

So what is it that such pickups "do" that lends itself to slide? For example, are they better able to pick up on the nuances of the string much later in the note's lifespan? Is it simply a tonal difference? Just what the heck do they accomplish that a standard strings-over-polepieces pickup won't do?

[David King]

Perhaps they pickup in x and y axis?

[bbsailor]

So yesterday I picked up the latest CD from Blake Mills. Absolute monster slide player, in the same league as Derek Trucks and Ry Cooder, yet able to play jazz progressions like Bill Frizell and mariachi music like David Hidalgo.

A number of the Youtube demos and live things I see from him have him playing a Strat-en-stein with a gold foil in the neck position and a horseshoe derivative at the bridge. Not split like a horseshoe, but the strings pass through it, rather than over it.

So what is it that such pickups "do" that lends itself to slide? For example, are they better able to pick up on the nuances of the string much later in the note's lifespan? Is it simply a tonal difference? Just what the heck do they accomplish that a standard strings-over-polepieces pickup won't do?

Mark,

All guitar pickups with magnets in the center of the coil will not produce a symmetrical signal as the lower dip of the string vibration will be closer to the magnet than when it is in its upward swing and farther away from the magnet. To test this just put an oscilloscope on a pickup and notice that one side of the wave form will be about 20 percent more than the other. When you go through a horseshoe magnet, there is a magnetic field both above and below the string so the output should be more symmetrical and my hypothesis can be easily tested with an oscilloscope. Let us know if you try to measure one.

Joseph Rogowski

[Mike Sulzer]

The asymmetrical shape that you mention is equivalent to saying that the signal contains even harmonics. Certainly they are produced by the non-linear process you mention. But even harmonics are also present because of the way the string vibrates. I think you would have to measure with pickups in at least two locations along the string and do some very careful calculations in order to demonstrate how much of the even harmonics are the result of each cause.

Mark,

All guitar pickups with magnets in the center of the coil will not produce a symmetrical signal as the lower dip of the string vibration will be closer to the magnet than when it is in its upward swing and farther away from the magnet. To test this just put an oscilloscope on a pickup and notice that one side of the wave form will be about 20 percent more than the other. When you go through a horseshoe magnet, there is a magnetic field both above and below the string so the output should be more symmetrical and my hypothesis can be easily tested with an oscilloscope. Let us know if you try to measure one.

Joseph Rogowski

[rjb]

...When you go through a horseshoe magnet, there is a magnetic field both above and below the string so the output should be more symmetrical...

With slide or steel guitar, I think it significant that the magnetic field balances the force on the string, allowing it to vibrate longer.

To some extent, you can get the same effect by installing a ferrous guard over the strings with a "regular" pickup.
I have an Electromuse lap steel with a removable steel hand guard over the pickup.
With the hand guard installed, you don't need a scope to hear the increased volume and sustain.

[Joe Gwinn]

With slide or steel guitar, I think it significant that the magnetic field balances the force on the string, allowing it to vibrate longer.

To some extent, you can get the same effect by installing a ferrous guard over the strings with a "regular" pickup.
I have an Electromuse lap steel with a removable steel hand guard over the pickup.
With the hand guard installed, you don't need a scope to hear the increased volume and sustain.

I think this is exactly right. The side pull on the string causes wolf tones if too large.

[Mark Hammer]

This is a provocative suggestion. One of the things one notices about both Mills' and Cooder's slide playing is their ability to wring expressiveness out of strings well after they would have died out on a 'normal' pickup. There is a sense of increased sustain, but without any electronic enhancement to accomplish it.

[Mike Sulzer]

That is an interesting suggestion, but then the same should be true for a blade pickup since the side pull should also be small. In any case, the side to side variation is smaller than that towards and away from the pickup (so called "vertical"). The former goes to zero when the string is centered over the pole piece while the latter does not. Also, for side to side, the field gets weaker for motion to either side, while the vertical force is stronger one way, weaker in the other. Thus the elliptical motion expected when there is no change in the magnetic field is more seriously altered. I would look for the explanation for string pull effects in the variation of the vertical field. But a little bit of experimentation could prove or disprove that.

I think this is exactly right. The side pull on the string causes wolf tones if too large.

[Mike Sulzer]

Another way to reduce the change in the field in the vertical direction would be to use an air core coil, and put a very strong magnet underneath. (Very strong to keep the magnitude of the field at the same level at the string) The further away the magnet is, the less would be the variation at the string. Making it deep and wide would also reduce the variation in the field at the string.

If it really is true that reducing the variation of the field reduces string pull effects, then one can make the field stronger than the usual standard. This could be useful when you want to put the pickup further from the strings, such as under the pick guard or under the top of an acoustic, making it possible to make up for much of the loss in signal sensed by the coil by using a stronger field.

I think this is exactly right. The side pull on the string causes wolf tones if too large.

[Joe Gwinn]

That is an interesting suggestion, but then the same should be true for a blade pickup since the side pull should also be small. In any case, the side to side variation is smaller than that towards and away from the pickup (so called "vertical"). The former goes to zero when the string is centered over the pole piece while the latter does not. Also, for side to side, the field gets weaker for motion to either side, while the vertical force is stronger one way, weaker in the other. Thus the elliptical motion expected when there is no change in the magnetic field is more seriously altered. I would look for the explanation for string pull effects in the variation of the vertical field. But a little bit of experimentation could prove or disprove that.

Blade pickups pull the string towards the pickup due to the non-uniform magnetic field. The "side pull" here is the force perpendicular to the string axis.

[ScottA]

Well, one thing to consider is that the pickup does not require a magnet at all.

The string must be magnetized, but given that, there is no requirement for the pickup to have a permanent magnetic field associated with it.

A ferromagnetic pole piece can help focus, direct and concentrate the flux, but even that is not a requirement. Given a magnetized string, an air coil will function as a pickup.

[Mike Sulzer]

Blade pickups pull the string towards the pickup due to the non-uniform magnetic field. The "side pull" here is the force perpendicular to the string axis.

So "side pull" is in the direction of the change in magnetic field, whether that be side wise or vertical in the usual use of these terms with pickup.

[Mike Sulzer]

Well, one thing to consider is that the pickup does not require a magnet at all.

The string must be magnetized, but given that, there is no requirement for the pickup to have a permanent magnetic field associated with it.

A ferromagnetic pole piece can help focus, direct and concentrate the flux, but even that is not a requirement. Given a magnetized string, an air coil will function as a pickup.

But the ferromagnetic pole piece also concentrates the flux from the vibrating string in addition to its effect on the permanent field from the magnet below.

[ScottA]

But the ferromagnetic pole piece also concentrates the flux from the vibrating string

I think I said that, didn't I?

in addition to its effect on the permanent field from the magnet below.

That's just "magnetizing the string". Just assume the string is magnetized, then the pickup is simply a receiver.

[Mike Sulzer]

I think I said that, didn't I?



That's just "magnetizing the string". Just assume the string is magnetized, then the pickup is simply a receiver.

OK, I thought you meant just the flux from the permanent magnet.

Yes, magnetizung the string. Now it is possible to say that without starting an argument with a certain former moderator who insisted that it did not happen.