Size of a faraday ring ?

[weiberheld]

Hello,
If I have a 3" voice coil that is 70cm long. How long and wide would the Faraday ring need to be to use it efficiently? Okay, I imagine it needs to be at least 3 inches but there are still more to consider?And where would be the best place to put it?

 

[weltersys]

If you have a 3" voice coil that is 70cm (27.56") long, you have something very unusual.
What is the Faraday ring for?

 

[diyuser2010]

I'd imagine he's talking about a copper or aluminum sleeve on the pole piece in the motor.