what's the formula for 3rd order Butterworth ???

Jocko, wouldn't you think that someone with knowledge of circuit analysis in the s-domain wouldn't be asking such a relatively simple question? :)

bbaker6212, I hope these formulas help.

For HP section with nominal resistance, Rh:

C1 (uF) = 1000000/(3*pi*Fc*Rh)
L1 (mH) = 3000*Rh/(8*pi*Fc)
C2 (uF) = 1000000/(pi*Fc*Rh)

For LP section with nominal resistnace, Rl;

L2 (mH) = 3000*Rl/(4*pi*Fc)
C3 (uF) = 1000000/(1.5*pi*Fc*Rl)
L3 (mH) = 1000*Rl/(4*pi*Fc)

C1/L2, L1/C3 and C2/L3 form a "T" circuit with the other terminals of: C1/L2 pointing towards the amp, C2/L3 points towards the speaker(s) and L1/C3 towards the ground.