low-impedance pickups thin

[charrich56]

I question that statement.
K&J's field calculator indicates that the steel plates will reduce the magnetic field at the strings, and confine it to an area spread around the magnets' perimeters. Which is probably a good thing.

K&J Magnetics - Steel Plate Thickness Calculator
Try entering
Grade: N35
Length: 20mm
Width: 10mm
Thickness: 2.1mm
Steel Plate Thickness: .009 in (.23mm) - the thickness of a typical "tin" can in U.S.A.

Then swap the Length and Width values to see a change in field "spread".
Of course, this doesn't show the interaction between adjacent magnets.

Enjoy.

-rb

EDIT: Of course, this also assumes that the K&J simulation is valid....

Thanks for going in-depth on this, my statement was intended to be very general and was not technically very accurate.

-Charlie

[salvarsan]

The K&J Magnetics sims are good as far as they go.

We spent a lot of time on 2D magnetic simulations using FEMM back in the '00s. Steve Kersting put up the best of them on his site.

explicit link:
Magnetic fields in pickups

They have both colored gradient images and graphs of magnetic field strength at string height. A baseplate can be a good thing to even out a magnetic field.

For a taste, here is a 2D sim of an AlNiCo5 PAF.

The field strength peaks ~0.0275 Tesla = 275 Gauss at 3/8" string height. FYI, Tele and P-90 pickups typically deliver 100 Gauss (or slightly less) at the string. You don't need much to get the sound you want, and probably should keep the field strength as low as is reasonable to minimize string damping.





It also shows that the magnetic aperture (50-100%) is about 2" which is at the heart of the PAF "vowel" sound because of comb filtering effects as discussed in Don Tillman's guitar pickup analysis.

explicit link:
Response Effects of Guitar Pickup Position and Width

Someone, if they were motivated, could relearn that clunky FEMM4.2 editor interface and put up a few sims of neodymium buttons with a skinny baseplate since I suspect that's all you need in a skinny pickup.

explicit link:
Finite Element Method Magnetics: HomePage

[rjb]

I Betcha There's Gotta be a Dot Product in There Somewhere....

Personal Background:
During a previous life, I took a class in electromagnetic fields, which had a prerequisite of vector calculus. However, I subsequently joined the circus (figuratively speaking), so never used that div, grad & curl stuff, and have long since forgotten it.

Question:
Is the basic argument/miscommunication/whatever between Mike & Salvarsan that "Sal" is looking at absolute values of field strength, while Mike is considering the y-components of field lines through the coils? Assuming that sentence made any sense?

Getting back to Thin Low-Impedance Pickups:
Is there a consensus that if you want to make a TLIP by sandwiching neo magnets between two sheets of steel, then the top sheet shouldn't be much thicker than "tin can" metal?

-rb