Using Copper clad board for flatwork.

[FunkyKikuchiyo]

Mike, I don't quite follow your last point... do you mean a conductive loop would need the flux lines passing through it mostly in the same direction in order for the loading to significantly occur? Would this by why adding copper shielding to a guitar has little/no effect on tone compared to shielding right on the pickup?

[Mike Sulzer]

Mike, I don't quite follow your last point... do you mean a conductive loop would need the flux lines passing through it mostly in the same direction in order for the loading to significantly occur? Would this by why adding copper shielding to a guitar has little/no effect on tone compared to shielding right on the pickup?

Yes. To get a clearer picture of this, consider the flux that matters to the coil: the flux from the vibrating string. A field line that passes through the coil continues out the bottom and makes a loop back up to the string. The geometry is such that most such flux lines return outside of the coil. So the coil sees mostly lines in the downward direction. And so does a shield placed right around the coil. Move the shield further out and more returning lines are enclosed within it, and the less the current flows around it.

[David Schwab]

I've got to say that if the copper loop on my pickup sure didn't reduce the high end the way you would expect! It was a very bright pickup.