* =============================================================================
* Woofer channel — Linkwitz-Riley 4th-order low-pass @ 300 Hz
* Signal chain: LPF(300 Hz) → LPF(300 Hz)
* Op-amps: OPA2134 macromodel, ±15 V
* Values from: python calculator.py 300 3000 --channel woofer
* =============================================================================

.param Clp1=68n Clp2=136n Rlp=5.6k

.subckt OPA2134X INP INM OUT VCC VEE
Gerr 0 NERR INP INM 0.01
Rp NERR 0 10Meg
Cp NERR 0 1.989e-12
Ebuf NBUF 0 NERR 0 1
Rout NBUF OUT 50
D1 OUT VCC DCLAMP
D2 VEE OUT DCLAMP
.model DCLAMP D(Is=1e-15 N=0.01)
.ends OPA2134X

Vin IN 0 DC 0 AC 1

* Stage 1 — Sallen-Key LPF 300 Hz
* WHY: passes bass to woofer amp; C2=2·C1 + equal R → Butterworth Q=0.707
R1a IN N1a {Rlp}
R2a N1a N2a {Rlp}
C1a N2a 0 {Clp1}
C2a N1a OUT1 {Clp2}
X1 N2a OUT1 OUT1 VCC VEE OPA2134X

* Stage 2 — identical → LR4 (24 dB/oct), −6 dB at 300 Hz
R1b OUT1 N1b {Rlp}
R2b N1b N2b {Rlp}
C1b N2b 0 {Clp1}
C2b N1b WOOF_OUT {Clp2}
X2 N2b WOOF_OUT WOOF_OUT VCC VEE OPA2134X

Rload WOOF_OUT 0 100k

VCC VCC 0 15
VEE VEE 0 -15
CdecP VCC 0 100n
CdecN VEE 0 100n

.ac dec 100 10 20k
.print ac Mag(V(WOOF_OUT)) Phase(V(WOOF_OUT))
.end