Active Filter: Linkwitz
(4th order, 24 dB/octave, Lowpass)

R=4.7k-10 kOhm
Ca=Cc=2*Cb
Cb=Cd=1/(2*sqr(2)*pi*Fc*R)

Units: R [Ohm], Cx [F], Fc [Hz]

Contributor: Joakim Ögren