Making the Shure Unidyne B 515SB sing

A great mic. After the bass heaviness and nastiness is removed by suitable inductor, inductor resistive filters the high frequency content that is revealed is great with no s problems, harshness etc.
This refers to the USA vintage model.


The original Fame soundtrack was playing in another room through the Pleiades 2N3053 millipower amplifier operating in class ie echelons flowing all the time.


In the mic singing, headphone reproduction room it was sing along time trying to match the sparkling purity and brightness of the original Fame soundtrack. The Grampian DP6/L does the trick without the need of an EQ. Just a WE 1:2 step up transformer to transform the impedance from 25Ω to 100Ω. So 100Ω was connected direct to Sony TC-D5 Pro through a phase inverter.


So what about the Shure 5151SB?


Here is the signal path that made it to this kind of sound.


male voice singing not loud at 1-9 in - mic - Pleiades (130Ω,40mH) gentle slope high pass - German transformer with primary inductance of 470mH - Western Electric 1:2, Lprimary=1H - Phase inverter - Sony TC-D5 Pro - Sennheiser HD580


(The 2 Pleiades filters may be combined in just a Neutrik module XLR to XLR barrel adaptor, perhaps a 1:2 transformer could be made that incorporates all 3 in a resistive wire primary winding)


Here is what each component more or less does:


The Pleiades 130Ω,40mH wave filter compensates for equal loudness curves and voice effort curves. Ie when voice is reproduced louder the human brain perceives more bass, when someone is singing softer the produced acoustic spectrum has more low and high frequency content compared to midrange. Without this filter the sound is bass heavy. Our brain knows why. Those are subjective effects which were measured thereby becoming objective by such phsycho physics or physchoacoustic pioneers such as Fletcher, Munson, S.S. Stevens etc.


The second filter is really the primary inducstnce of the German e+p GSM1 transformer with the switch in the 1:(1.something) position ie from 500Ω to 600Ω. This filter apparently compensates the proximity effect. It is not needed if a distance of say 9in is used. But when a distance of 1in is used it creates approximately the same subjective result. This filter removes also of course the very low pop, ambient, handling noise too.


The phase inverter XLR barrel is used to make positive pressure on mic create positive pressure on headphones to avoid bass cancelation while listening (troughs air and through headphones) and singing in real time.


The Western Electrc 1:2 transformer transforms the 200Ω or so mic output impedance to 600Ω so as the generously drive the Sony mic (with input transformer) input. It also creates some low cut by at a low frequency since the primary inductance is 1 Henry.


The Sennheiser HD580 are very neutral,sounding headphones. For a few hundred dollars one can monitor at such quality as a multi million worth control room. It is like the magic mirror telling the truth.



See also:


Flat frequency response from singer's vocal chords to listener's brain, Sound Picture Recording a Reproducing characteristics - D. P. Lowe, K. F. Morgan - Journal of the society of motion picture engineers