Monday, August 29, 2016

Close distance equalizer

Close distance microphone equalizer may be a more usable term for proximity effect compensating low cut filter.


A Pleiades filter is just an inductor in parallel with the microphone to do just this, attenuate the bass that is increased by using a directional microphone close.


When we use a directional microphone at very small distance even 500Hz is increased 400Hz even more 300Hz even more etc. So a Pleiades filter of 500Hz cutoff can be used to make the overall response flat from 100Hz to as high as the microphone can hear. We can still increase or reduce bass in voice by moving close or further from the optimum distance. (Examples of proximity effect for any distance can be seen on the AKG D310 frequency response curves.


The optimum distance depends on the microphone, the Pleiades filter cutoff, the singer, the end result wanted etc.


The Pleiades filter cutoff depends on the number of insulated wire turns wound on the magnetic core. Toroidal cores are very suitable as they as balanced even geometrically. They can do the trick with relatively few turns.


The process reminds photography were at close distance a macro lens is needed. Different Pleiades filter cutoff frequencies are used depending on the distance.


Pleiades filters can be combined together (one after the other). This is easy if each is made inside an XLR female to male adapter. So not many are needed as can be seen from earlier euroelectron posts.

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