Does the pickup covers (Nickel, Gold) Effect sound?

[thanaton]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

In essence we agree aside from it sounds like you're saying that the current develops only if the speed is changing. And that's not the case in the tube drop for example. If you travel at a brisk enough speed and continue at that exact same, fixed speed, the currents develop and continue to be developed. It's not only a change in speed. It sounds like you're suggesting if the acceleration was slowed down, the currents would not develop even when the magnet reached the faster speed. Maybe that's not what you meant.

What I disagree with is the notion that eddy currents are proportionately lower if a player picks lightly. The same flux change that created the eddy current is the same flux change that induces voltage. There's no reason why the relationship between the two would not be linear. It's not as though picking lightly can somehow avoid eddy losses, but still induce a strong voltage in the coil. Where one goes, so goes the other.

In general, I agree that eddy losses owing to the cover are not a big deal, and can be overcome by using higher value pots or by increasing the treble on the amp. Since the losses are linear, there is no informational loss, and the only real downside is a poorer signal to noise ratio, for having to boost the treble.

Also, I don't mean to single you out. Your posts just happen to be ones I felt inclined to respond to.

 

[uOpt]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

I'd never tested, but does it matter what the cover is made out of? Do gold plated covers sound different than chrome?

Just to say the obvious, if it is magnetic all hell breaks loose. There were a few Asian knockoff pickups that made that mistake, and I think some exotics. Wasn't Rickenbacker also stepping into that trap at some point?

Eddy currents are, btw, the reason why I don't advocate to shield the cavities of a Stratocaster pickup route. It won't do much do reduce single coil hum anyway and it will kill some of the treble.

 

[thanaton]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

Eddy currents are, btw, the reason why I don't advocate to shield the cavities of a Stratocaster pickup route. It won't do much do reduce single coil hum anyway and it will kill some of the treble.

Metal below the pickups makes a much lower impact. Shielding a Strat's pickup cavity doesn't even begin to compare with the base plate on the Tele bridge or a PAF style humbucker, in terms of thickness and proximity.

 

[uOpt]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

Here is the formula (thanks wikipedia.

https://en.wikipedia.org/wiki/Eddy_current

P is the power lost per unit mass (W/kg),
Bp is the peak magnetic field (T),
d is the thickness of the sheet or diameter of the wire (m),
f is the frequency (Hz),
k is a constant equal to 1 for a thin sheet and 2 for a thin wire,
ρ is the resistivity of the material (Ω m), and
D is the density of the material (kg/m3).


So as you can see, the force goes up quadratic with thickness of the material, and it goes up quadratic with frequency.

Resistance of the material in only linear. So clearly if you want to minimize it is better to use thinner covers even if that means you have to also reduce resistance.

The strength of the magnetic field is also square here. Now it gets complicated, because the way that I see this now eddy currents influence the sound mostly by magnetically dampening the string (as opposed to changing electrical parameters of the low-pass-filter that the coil is).

It also means that the cover itself is under electromagnetic force trying to move it relative to the rest of the pickup. That can very easily make an audible difference.

 

[uOpt]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

Metal below the pickups makes a much lower impact. Shielding a Strat's pickup cavity doesn't even begin to compare with the base plate on the Tele bridge or a PAF style humbucker, in terms of thickness and proximity.

Yes, but in the case of a Tele or a hummelbucker it is part of the desired sound.

Our Stratocater slinger idols do not have conductors under the pickups, except maybe for Blackmore depending on year.

 

[thanaton]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

Here is the formula (thanks wikipedia.

https://en.wikipedia.org/wiki/Eddy_current

P is the power lost per unit mass (W/kg),
Bp is the peak magnetic field (T),
d is the thickness of the sheet or diameter of the wire (m),
f is the frequency (Hz),
k is a constant equal to 1 for a thin sheet and 2 for a thin wire,
ρ is the resistivity of the material (Ω m), and
D is the density of the material (kg/m3).


So as you can see, the force goes up quadratic with thickness of the material, and it goes up quadratic with frequency.

Resistance of the material in only linear. So clearly if you want to minimize it is better to use thinner covers even if that means you have to also reduce resistance.

The strength of the magnetic field is also square here. Now it gets complicated, because the way that I see this now eddy currents influence the sound mostly by magnetically dampening the string (as opposed to changing electrical parameters of the low-pass-filter that the coil is). Conductive steel slugs would cause greater losses in relation to the coil, since they are in the coil's core.

It also means that the cover itself is under electromagnetic force trying to move it relative to the rest of the pickup. That can very easily make an audible difference.

A cover definitely has a greater effect on the string that the inductive properties of the coil, since it's creating that opposing field right in between the two, like a road block, but as the equation points out, it's still a frequency dependent loss, even if it's not altering the electrical properties of the coil.

I'd be willing to bet that any drop in Q factor tells us what portion of the eddy current losses apply to the string, versus that which applies to the coil. If the losses are purely in relation to the string, the Q should remain intact, but when the eddy currents reduce inductive reactance in the coil, the Q factor will then drop.

 

[Mincer]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

I appreciate the clarification. Since I never did A/B tests, I always figured the material the cover was made out of must have some effect. I am guessing something non-metal does something to the sound, too.

 

[thanaton]

Re: Does the pickup covers (Nickel, Gold) Effect sound?

I am guessing something non-metal does something to the sound, too.

If the material is neither conductive nor permeable, then it should be inconsequential to tone.