They're 30 db/oct. They're CLCLC. So 5 poles * 6 = 30. A 600 ohm in / out LC filter has to start with the same component type and orientation to have the same characteristic impedance in and out. So it has to be odd numbers of elements. The Pultec HLF3C is 3, the Allison Labs 2BR / 2ABR are 5. The low cut is capacitors in series and inductors as shunts. The high cut is capacitors as shunts and inductors in series.I believe they are rated at 24dB/oct, not 30. Could be wrong.