Electro Voice RE15 and Beyer M55

The RE15 was used with its low cut on. This is an inductor in parallel with the voice coil output, a Pleiades filter.


It sounded amazing at a few inch with a very strong signal output.


Then a Pleiades filter of 160mH, ie 200Hz, was added in line between the mic body XLR out and the female cable XLR.


Now the mic could be used at 1-2in for the same timbre and full spectrum on voice. Of course the signal was even stronger as the mic is much nearer to the source. The signal to noise ratio is phenomenal as all ambience was low cut and only a slight hiss left.


Then the Beyer M55 was connected without any Pleiades filter and used at 0-1in.


The sound was phenomenal and there is something even more dynamic about it. Perhaps more fullness of sound, dynamic and great smooth treble detail. Some ambience could be heard but it sounded nice as it had a natural frequency spectrum. This should not cause a problem as at 0-1in the voice signal is phenomenally strong.


On very noisy situations one can use Lou Burroughs (co-founder of Electro-Voice) trick of
connecting another same omni mic out of phase and singing to one of the mics. It is described in his book Microphones, design and application. An easy way to connect both mics together in series like batteries (a mic is a generator of voltage) is described in the next euroelectron post.


In those tests it must be remembered that the input transformer used has a primary inductance of 400mH which is another Pleiades filter giving a low cut of 70Hz. To find the total cutoff that must be used for correct frequency responce from vocal chords to listener's brain one needs to add all those cut off frequencies to find the resultant cutoff needed.


Then a Pleiades filter or a Pleiades input transformer can be made with the corresponding calculated primary inductance. 200Ω divided by 2 divided by 3.14 divided by the cutoff frequency needed and that equals the inductance needed to be connected across the mic output. The primary turns wanted will turn out to be few. And if a transformer is made it may be of a high step up ratio.


One must also take into account that the particular Beyer used is 500Ω. The RE15 is 200Ω so it can be used with a higher step up transformer ratio to give an even louder signal.


Signal path, setup:


Moving coil directional or omni mic - Pleiades filter (in case of the RE15 in addition to its low cut on) - Canford input transformer with primary inductance of 400mH - Pleiades V4, EF183 operated with 3.4volts - Realistic disco mixer at mic mono input - HD580


(The M55 was connected straight to the Canford input transformer)