opinions for those who know: polarization voltage on backplate vs diaphragm?

What's the difference in sound/tone?

Dear 777funk,

no difference if the amount of voltage polarization is the same.
the only difference is that if you put the 60V on the diaphragm, it will be more prone to collect dirt with time.And you have to use a coupling capacitor between the diaphragm and the tube grid.

regards
fred

First of all: capsule is capacitor with three layers.
For the U47 schematic:
If the bias voltage is applied to the central electrode , the matter which figure is used .  If cardioid, ie small effect unconnected side of the membrane to the total work of the capsule . When applying a polarizing voltage to the central electrode , on both sides of the capsule is formed opposite sign equal in magnitude to the potential applied to the electrodes - it is  Coulomb's law. Of course, when working in cardioid, the second side of the capsule is not connected to the grid of the tube and theoretically its influence is not taken into account. But actually on the unconnected side there is a small change in potential as the membrane under the influence of air flow still fluctuates and these fluctuations but very little effect on the overall operation of the capsule . This effect on the level of a percent , but it matters . Therefore, more correctly supplying power to the diaphragms and not the central electrode. Then the work of the capsule is more precise and correct .

Very interesting!

granger.frederic said:

...no difference if the amount of voltage polarization is the same.
the only difference is that if you put the 60V on the diaphragm, it will be more prone to collect dirt with time.And you have to use a coupling capacitor between the diaphragm and the tube grid.

Click to expand...

This is what I've always thought.

o3misha said:

...But actually on the unconnected side there is a small change in potential as the membrane under the influence of air flow still fluctuates and these fluctuations but very little effect on the overall operation of the capsule . This effect on the level of a percent , but it matters . Therefore, more correctly supplying power to the diaphragms and not the central electrode. Then the work of the capsule is more precise and correct .

Click to expand...

This is news to me. I'm not sure I understood you correctly. You're saying the movement of the unconnected membrane affects to the potential of the backplate?

Is this why there are many cardioid only mics that polarize the membrane, when they could polarize the backplate and get a way with one coupling cap less? Chinese mics and Oktava comes to mind. I've always thought they're just bad implementions of the SDC designs with grounded backplates. (Though I questioned that when I noticed that a high end boutique cardioid mic I have also polarizes the membrane, and it definitely is not a SDC circuit copied to LDC world).

if you have a dual side capsule, the movement of the rear membrane affects mechanically the movement of air inside the capsule ,and it's well known.
However if the rear membrane is disconnect electrically, it couldn't affect the electrical signal.
I add that if the schematic is in cardioid: 0V-60v-0v or 60v-0v-60v, then only an approximation of the rear or front polarization voltage could affect the pattern thus the frequency response.

Cheers
Fred

I meant that not connected to the tube grid second half of the capacitor (capsule) continues to change a little its potential when capsule works( charging-discharging) .  Inactive second membrane also moves a little, and therefore changes its potential which is already not equal negative to polarizing voltage  (Thats a main thing! Capsule is not static element!!). How can stabilize potential changes on the inactive membrane ?-that's what the main issue. A redistribution of the accumulated charge of the second membrane around the  all capacitor (capsule) - is a natural process for any condenser. The effect of these processes are insignificant, but they contribute to signal distortion, as these affect the charge sharing operation of the entire capsule. However, the second method - the polarization of the diaphragms and the ground of the central electrode (the second method, which is used in most microphones),-  these artifactual current fluctuations are excluded completely. That's all! The second method is more correct.