After plenty of tests with Sennheiser MD-421 microphone at next to mouth distance a range of high cutoff frequencies were tried to compensate for the proximity effect. A range of 14mH to 25mH of Pleiades Filter shunt inductance gives natural voice. This corresponds to 2.2KHz to 1.3KHz at 200 Ohms mic output impedance.
This also agrees with frequencies of less than 1.5KHz being proximity boosted at small distance as seen on curves on Shure's catalog for their Beta 58.
A Pleiades inline filter of 20mH has been made and was given to singer Sophia Manousaki by Stephanos Korkolis. !.6KHz may be just perfect for a female singer giving flat overall frequency response at speech level voice.
A winding of suitable series resistance could be used to stop the Pleiades filter compensating below 150Hz as an SM58 already drops at 6dB per octave.
Ferrite cores seem more suitable as they can take much more winding length for the same inductance.
A Siemens Epcos ferrite of small size and 102 turns giving 15.5mH and 3 Ohms resistance gives promising results with sound body. Should a winding of 20 Ohms be used to create a second turnover at 200Hz?
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