Effect of a Faraday ring...

[Cloth Ears]

What is the effect of a Faraday in a driver, please? Specifically, the effect of 2 as compared to one - like in Nick McKinney's Apollo motors for his TD drivers.

The old prices, when Nick was running Lambda, listed the TD15 drivers at $179 for the "no Faraday motor, $279 for the "one Faraday motor" and $479 for the "two Faraday motor" (the Apollo). Was it worth the difference?

This is just for interest, as I saw a set of 4 for sale on the Trading Post thread, and I wondered...?

[cotdt]

i couldn't find much info on this either, other than faraday rings making the motor more linear by preventing the pole piece's magnetic field from being modulated by the current through the voice coil.

[Cloth Ears]

Thanks cotdt,

We'll see if there's any other responses. BTW the Apollo Lambdas were triple Faraday...

[cotdt]

I found this link by some Feyz guy:
http://www.geocities.com/pirimoglu/A...lImpedance.pdf

[Bill F.]

BTW the Apollo Lambdas were triple Faraday...

If it's an arms race, the JBL 1500AL leads the pack with 15 copper faraday rings in the gap and one aluminum sleeve over the magnet...

Seriously, though, Feyz's document is a must-read.

As to the effect of multiple vs. single, everything depends on the geometry of the rings. Sandwiching the entire travel of the VC between single full-length outer and inner copper sleeves would deliver maximum shorting effect.

[cotdt]

why is copper used over aluminum? wouldn't aluminum shorting rings work just as well?

[Bill F.]

Copper has somewhat lower resistivity and better thermal transfer, but Al isn't bad, either.

[paulspencer]

As I understand, shorting rings are also called flux modulation rings, and servo to reduce inductance, reduce distortion and make a driver more linear when more power is used. It's interesting to note that most Adire audio drivers don't use shorting rings, I've seen Dan Wiggins comment on the SI forum that in some cases the improvement is subtle and not worth the extra cost. Apparently Eminence were asked to make a verison of the Lab sub driver with shorting rings but they declined due to the cost of getting it to work effectively for a subwoofer with large excursions. However, the new Dayton Reference subs use them and are affordable. The Rythmik audio servo driver also uses a shorting ring and it seems that most subs that measure well regarding distortion have them.