(Sorry for my English!!)

I'm from Brazil and I saw this post, and I still have a doubt!

I have a bi-amplified system (two-way sytem or called component sytem) and a active crossover before de amplifier.

The first doubt:

I will put a zobel network and I need to know if can I put it between the amplifier and the speaker directly (without passive crossover)?

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The second doubt:

Wich formulas above is correct to find the value of the capacitor to build the zobel?
f= Frequency impedance double
pi = 3,14....
Rvc = Re = Resistance of teh coil voice

C = 1 / (2 X pi x f x Rvc)

http://sound.westhost.com/lr-passive.htm#1-impedance

or
C(microfarad)= 1,000,000/(6283 x Nominal impedance x f)

http://www.the12volt.com/caraudio/crosscalc3.asp#zobel
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The third doubt:

To find the frequency impedance double wich formulas is the correct?

Lvc = Le = Inductance of the voice coil

f = Rvc/ (2 x pi x Lvc)

or

f = 2 x Rvc? This means Frequency impedance double, but the values are different!!

Thank you very much!!

Vinicius