Another moving coil mic that sends to the cleaners mics x100 or x1000 more expensive.
Gives hard time to condenssers as it brings out detail to sounds dozen of yards away. It can sound with edge as condensers do, it is quite smooth at the same. And sibilants are fine, not as good SSSes as an MD21but it sounds very natural.
Thanks to Martin Mitchell's website very nice sounding audio sample and excellent review it was decided to give it a try.
Signal path, setup:
Grampian DP4/L - Pleiades V6 with either Altec 4722 or Pleiades 140mH input transformer- Sony TC-D5 Pro - Sennheiser HD580 precision headphones
It was thought that it will sound thin with no bass. So the 1:10 Pleiades input transformer with 140mH was un pluged from the experimental jig and the Altec was inserted. The Altec has about 300mH primary inducatnce at the 200 ohm tap.
No the bass was great. Full, natural and not emphasized.
In fact the is a very rare case of a microphone that sounds flat to listener's brain without the need of any EQ.
As on Martin's website an L type, low impedance version was tested.
The impedance is 25ohms.
There is something really nice with low impedance. It is a few turns just like SM57, 58 microphones. It seems this makes a lighter voice coil and better transient response. The SM58 family has an internal transformer to step up the low Z to a typical 200-250ohms.
So it was decided to connect the 25 ohm coil to the 38 ohm tap of the green Altec transformer.
A possible pitfall is that the Pleiades V6 EF183 electron tube has a typical input resistance of 100Kohms at the particular electron accelerating conditions needed for battery 3.9V anode operation. A 8 Megohm resistor is connected from anode to grid and this has the effect of lowering the grid impedance to around 100Kohms, not a bad thing but the Grampian would be loaded.
But it sounded great with a natural and full sound, loud, revealing. Al the ambience could be clearly heard.
When it was connected to the 150ohm terminal the sound was great too with more treble and of course somewhat less output.
Then the Pleiades 140mH was connected. And it sounded great too. Still with bass. And loud. It is saved by the that it's low Z out is not loaded by the low 140mH inductance, so bass remains. Just a reminder, the reactance of an inducatance in ohms is 2 x 3.14 x frequency x inducatance. And there is a potential devider formed. So at low frequencies the mic is loaded and there is voltage drop it its internal impedance (conservation of energy). This internal impedance is also called the output series resistance, (Norton's, Thevenin's theorems).
Compared to MD21 HL. The MD21 sounded more treble and bass extended. But a bit like having a woofer and a tweeter. So better or not, it depends on the application, voice, type of singing etc. A very impressive fact of the Md21 is that there is almost non sibilant problems. The Gramian was as good as it can be it that respect.
The MD21 had greater output which is natural since it is 200ohms. So immediately a BBC 1:1.8? transformer was included to make the impedance from 25ohms to 80?ohms. The 80 ohms or so fed the Pleiades V6. There was still bass and the sound was brighter.
One other interesting thing about the DP4 is that is sounds great at greater distances. It really shines at 4-8in for example. When the mic was even further away it still sounds very clear whereas the MD21 less so in an untreated room. The ambience with the MD21 even when connected to as low inducatnce as 140mH is quite bass heavy.
The ambience with the Grampian did not sound bass or treble heavy. It was a joy listening to a radio playing 3 rooms away through it, very natural. very similar to ear sound capture.
And female speaking voice at 24 feet sounded very realistic.
Of course birds singing could be heard yards away even with double glassed windows.
When the headphones were removed the acoustic ambience sounded more like Grampian than MD21.
Summary:
Another case of a rare mic that has flat frequency response from singer's vocal chords and not on;y, to listener's brain and therefore natural sound.
It sounds a bit with metal edge. Is the diaphragm made of aluminum? This is not nessesarity a bad thing. Ribbon mics are nade of aluminium moving element although it is much ligher.
Another great sounding mic with excellent transient response that can sound as bright and detailed as you wish while being smooth (see other euroelctron posts) is the Grampian GR1/L ribbon.
British high class.
Reference:
Electronics, a System's approach - Neil Storey
Flat frequency response from singer's vocal chords to listener's brain, Sound Picture recording and reproducing characteristics - Loye, Moran - Journal of the Motion Picture Sound Engineers
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