Cryogenics

[Joe Gwinn]

Exactly. This is why if you are really interested in good hum rejection, multiple coil pickups can be useful. Field gradient effects are most important in the long dimension of the pickup. So if you keep one dimension small by making single coil size pickups and then use multiple coils in the other dimension, you can do better. Six coil pickups with alternating sensitivity can be good, as well pickups using six pairs of coils. Coils can be connected together, effectively making a gradient canceling pickup, or they can be used to amplify each string individually.

I recall discussing such multicoil cancellation schemes, which are used in intrumentation, in a thread some time ago. I think the thread had to do with dummy coils.

The conclusion was that these schemes were probably overkill for guitars. Part of the practical problem was that the coils needed to be symmetrically arranged to cancel non-uniform fields up to some order (constant being zero order, and so on), and the needed physical and electrical symmetry and pattern of coil locations quickly became difficult to implement in a guitar body, and cost soon exceeded benefit.

[Mike Sulzer]

I recall discussing such multicoil cancellation schemes, which are used in intrumentation, in a thread some time ago. I think the thread had to do with dummy coils.

The conclusion was that these schemes were probably overkill for guitars. Part of the practical problem was that the coils needed to be symmetrically arranged to cancel non-uniform fields up to some order (constant being zero order, and so on), and the needed physical and electrical symmetry and pattern of coil locations quickly became difficult to implement in a guitar body, and cost soon exceeded benefit.

I do not remember that discussion; so I will look for it later. I think you are right about the limitations; you cannot do it perfectly in a guitar due to a number of constraints. But you can make it better than normal. I do not think that hum cancellation is ever better than necessary. More gain without annoying hum is always what a certain fraction of electric guitarists want!

[Joe Gwinn]

I do not think that hum cancellation is ever better than necessary. More gain without annoying hum is always what a certain fraction of electric guitarists want!

Yes, but the question is when the hum becomes imperceptible, not just in the lab, but in a noisy gig venue. My instinct is that 20 dB is enough for the gig, and 30 db for the lab.

[Rick Turner]

The biggest problems with hum canceling these days are not in noisy gig situations, they're with sitting down in a home studio trying to record while surrounded by heaps of hash radiating electronics and wall warts.

That said, one of the worst venues I ever was in was on Sherman Way in Tarzana or some such San Fernando Valley place. The electrical service panel for that fairly large building was on the opposite side of the wall from the very small stage.

[Joe Gwinn]

The biggest problems with hum canceling these days are not in noisy gig situations, they're with sitting down in a home studio trying to record while surrounded by heaps of hash radiating electronics and wall warts.

Right. That's a acoustically quiet "lab" situation.

That said, one of the worst venues I ever was in was on Sherman Way in Tarzana or some such San Fernando Valley place. The electrical service panel for that fairly large building was on the opposite side of the wall from the very small stage.

In a gig, the acoustic noise maskes the hum, and everybody is drunk anyway, so who cares anyway...

By the way, service panels don't usually emit much of a hum field. Transformers and motors are far more dangerous.

[Rick Turner]

They might have had a 3 phase transformer back there.

We have our own here in my shop for our single phase needs.

[Joe Gwinn]

I do not remember that discussion; so I will look for it later.

If I recall, the words "gradient" and "gradiometer" were used.

[David Schwab]

The biggest problems with hum canceling these days are not in noisy gig situations, they're with sitting down in a home studio trying to record while surrounded by heaps of hash radiating electronics and wall warts.

And light dimmers! I was playing a gig recently and my normally very quiet humbucker equipped bass was humming like mad. I thought something was wrong until I realized the two guitarists humbucker equipped guitars were humming too. The room had a profusion of light dimmers.

Another situation was in a guy's basement studio. There was this crazy whining/chirping sound getting picked up by everything. It turns out he had one of those "invisible fences" for his dogs. When he shut that off the noise went away.

[Joe Gwinn]

Another situation was in a guy's basement studio. There was this crazy whining/chirping sound getting picked up by everything. It turns out he had one of those "invisible fences" for his dogs. When he shut that off the noise went away.

This could be a major discovery: We can use an Invisible Fence to herd guitarists! Who knew?

[salvarsan]

This could be a major discovery: We can use an Invisible Fence to herd guitarists! Who knew?

Used to be, you could only heard them singly by waving sheet music at them.

There's no chance this thread will _ever_ get back on topic, is there?

-drh

[David Schwab]

There's no chance this thread will _ever_ get back on topic, is there?

Topic? We don't need no stinkin' topic!

[Rick Turner]

It'll be a cold day in Hell before this gets back to it...

Oh, with climate change, Hell may freeze over as life here gets a bit warm...