Autotransformer for adjustable microphone proximity effect filter

This may be considered a variable Pleiades filter with input transformer gain.


The variable autotransformer (variac?) is connected in reverse. The low inductance variable side becomes the input for connecting the microphone. The normal input to the autotransformer becomes the output.


It should be possible to adjust for any directional microphone, any microphone distance for natural auditory perception.


It may be thought as the analog to the focusing adjustment of cameras according to the subject distance or the macro adjustment for a close up distance.


Added advantage is the automatic stepping up voltage as the primary inductance is decreased.



This is why:


As a singer gets closer to the microphone more bass reduction is needed to compensate for the proximity effect.


Therefore less primary inductance is needed.


Therefore less primary turns are selected by the rotary knob.


Therefore higher turns ratio takes place as the secondary is fixed.


Therefore we have a stronger signal.


In fact there are two effects added while voice is made to sound natural.


The signal is stronger as the singer is closer x the high step up ratio (which further multiplies the signal).


This should give a very strong signal ready to feed an ultra low noise, (one electron tube) preamplifier such as the Pleiades V4 for unheard sentitivity, loudness and low noise. Microphones in general can sound much more full in sound when there is an active stage of just one electronic device as inside the Neumann U47 for example.


Setup, signal path:


Moving coil mic - autotransformer - Pleiades V4, Vb=3.4V - realistic disco mixer mono mic input - Sennheiser HD580


Balanced signal output should be preserved as the output of the autotransformer is a coil.


The reduced high frequency responce at very high turn ratios may be beneficial too as it would compensate for increased high frequency perception due to Flether-Munson and voice effort (curves) psychoacoustic effects.


So we have an adjustable way to create a flat frequency responce not from microphone to loudspeaker but from the vocal chords of actor or singer to the brain of the listener at any distance.


Small distance has the advantage of hiding most acoustic problems, including noise.