Phase Shift Reference
Illustration in preparation Description: Phase response curves for 1st through 4th order Butterworth and Linkwitz-Riley filters, showing phase at crossover frequency for each
Phase at crossover frequency:
| Filter order | Type | Phase at Fc |
|---|---|---|
| 1st (6 dB/oct) | Butterworth | ±45° |
| 2nd (12 dB/oct) | Butterworth | ±90° |
| 2nd (12 dB/oct) | Linkwitz-Riley | ±90° |
| 3rd (18 dB/oct) | Butterworth | ±135° |
| 4th (24 dB/oct) | Butterworth | ±180° |
| 4th (24 dB/oct) | Linkwitz-Riley | ±180° |
Why LR4 is preferred: Both HPF and LPF are -6 dB at Fc (not -3 dB like Butterworth). The sum of both is flat. Phase is identical for both — no cancellation. Industry standard for professional active crossovers.