Pleiades (R,11mH) filter experiments with the Sennheiser MD 441U3, Fostex M55RP, Electro-Voice RE15

At your risk. Protect your hearing.


After experimenting yesterday with a Pleiades (R,L) filter for the Shure VP64 (see yesterday's post) it has been decided out of duriocity to try such a (low R,11mH) filter with a Fostex M55RP, Sennheiser MD 441U3 and Electro-Voice RE15 microphone.


All these mics are of the order of 200Ω so a 1:2 transformer with 1 Henry input inductance was used to step such impedance to 800Ω and then feed the Sony preamplifier.


Signal path:


Male voice singing at a high register - mic at 1in - Pleiades (R,11mH) gentle slope low cut or high pass filter - Western Electric 1:2 signal transformer - Sony TC-D5 Pro - Sennheiser HD 580 - singer's brain as listener's brain


With the yesterdays filter set at (37Ω,11mH) the M55RP sounded amazing.


So did the the MD441 U3.


The RE15 sounded reasonant at some high frequency band. In fact the sound might had been similar to the VP64.


Encouraged by the beautiful, easy, sparkling and natural sound of the M55RP, and MD 441U3 the multi turn variable resistor was adjusted while singing in order to find sweet spots.


After finding a nice adjustment the crocodile cable clips are disconnected from the variable resistor and its value is measured with a digital voltmeter,


It is stricking that repeating the experiment 2 times with the M55RP the values measured where 19Ω and then 20Ω.


Then while performng the experiment with the MD 441U3, the value measured was 24Ω.


So a Pleiades filter of about (22Ω,11mH) gives a beautiful sound with both mics at 0-1 in.
A bright sound but with no s artifacts. An amazing sound reminding the vocals of The Power of Love - Frankie Goes to Hollywood. Or the amazing When I Fall in Love - Nat King Cole


It is amazing what can be done with just an inductor connected in series with a resistor and the total connected in parallel with the mic's output or voice coil.


This Pleiades (22Ω,11mH) filter will possibly be built inside a Neutrik module XLR barrel adaptor. The color stripe in the centre already painted by nail varnish is light green, Annie color code 257.


The (130Ω,40mH) filter used with 600Ω Fostex microphones has a blue (Annie 245) stripe adaptor housing.


What is the difference in sound between the M55RP and MD 441U3 with such a Pleiades filter?


Hard to describe in words. Both mics sound amazing. They have the detail of ribbon mics. It is surprising that the MD441U3 may have sounded even more neutral. But the M55RP has perhaps some more presence. This is perhaps expected as the MD441U3 has a flat frequency response.


If a Pleiades Fikter is not connected, all that can be heard is bass and mid exaggeration by the well known objective and subjective effects described in the Lowe, Morgan paper.


Reference:


(Flat frequency response not from mic to loudspeaker but from singer's vocal chords to listener's brain) Sound Picture Recording and Reproducing Characteristics - D. P. Lowe, K. F. Morgan - Journal of the Society of Motion Picture Engineers