Cutoff frequency for Pleiades low cut proximity compensating microphone filters

By using almost any directional microphone experimentally or looking at published frequency response curves for small distance, we can see (hear) the following:


The proximity effect affects frequencies that are right into the human vocal band when directional microphones are held at the usual distance of 9in to 1in from mouth.


So the Pleiades low cut filters must have a cutoff frequency anywhere between 200Hz to 677 depending on application. This corresponds to 160mH to 47mH. An input transformer with 47mH primary winding inductance is used on the Pleiades V5 electron tube battery preamplifier and compensates greatly for Electro-Voice RE16.