why are some single coils noisier than others

[Rosewood]

Even with similar specs some just seem to be noisier, is it the layering of the wire that makes the difference? Other than shielding what would help on noise?
obviously lower resistance would help but is that all that can be done?

[Mark Hammer]

By "noisy" do you mean only hum or do you include hiss as well?

[Rosewood]

Mark, I was mainly talking about 60 cycle hum.

[John_H]

A ground loop can cause hum.

[Joe Gwinn]

Assume that the same coil is used for all the pickups in a series, and that it is electrostatically shielded.

Then, the more soft iron (baseplate, backer bar, slugs, et al) is near the coil, the more concentration of the ambient hum field there will be, and thus the more hum. Music will also be enhanced, so the question is the ratio of music to hum, not just how much hum one hears when not playing.

[soundmasterg]

Yeah, this is something I've wondered about over the years too. The P90 hums a lot more than most single coils, and by what you're saying Joe, I would guess it is because of the extra metal in the magnetic field, and the fat that it has a particularly strong magnetic field due to two bar magnets? As compared to a Strat pickup, the P90 has lots of extra metal in there.

Greg

[Rosewood]

I guess that would leave something like field focus (lace) to play with. The Lace sensor has more metal but they seem to have tamed some of the hum, not that I'm a fan of Lace sensors.

[Joe Gwinn]

Yeah, this is something I've wondered about over the years too. The P90 hums a lot more than most single coils, and by what you're saying Joe, I would guess it is because of the extra metal in the magnetic field, and the fat that it has a particularly strong magnetic field due to two bar magnets? As compared to a Strat pickup, the P90 has lots of extra metal in there.

That's extra soft magnetic metal. Alnico counts for very little, and ceramic for nothing.

[soundmasterg]

So the more soft metal in the magnetic field, the more hum?

Greg

[Joe Gwinn]

So the more soft metal in the magnetic field, the more hum?

Near the coil, actually. If there is also a magnetic field, the coil will in addition generate a music voltage, and the more soft magnetic material nearby, the greater the music voltage.

These are big generalizations, and the physical arrangement of things, not just the total mass of metal, matters a lot. But still the generalization is useful.

The real issue is the music-to-hum ratio, larger numbers being better (quieter), not just the absolute hum voltage. So, it's a bad test to just hook things up, crank the volume up, and stick an ear into the speaker.

A better test is to play the setup, and judge the overall effect. Or have someone else play, while you sit ten feet away and do the judging.

[David Schwab]

Also... ground all your metal parts, including magnets.

[soundmasterg]

So to give an example, the P90. Why does this pickup hum so much if you compare it to a Strat pickup for instance? Is it because there is a metal baseplate and two magnets in there?

[Dave Kerr]

According to Joe G (and others), hum reception is a function of the product of number of turns and the average area of the turns. P90's have a high number of turns and a wide coil form factor.

[black_labb]

So to give an example, the P90. Why does this pickup hum so much if you compare it to a Strat pickup for instance? Is it because there is a metal baseplate and two magnets in there?

im no expert, but i can imagine it being atleast partly to do with having a larger surface area to recieve the hum signal. the outside of the coils probably act as a shield for the inner coils.

[Rosewood]

So it looks like a small tight coil without soft metals, strat style, is about as good as it gets. I can see where a large coil could be like an antenna, probably like the Suhr system. The larger and noisier the dummy coil is, the less wire would be required, right?