Capsule Drawings/Designs for Large Diaphragms

[abbey road d enfer]

I've measured the capacitance of all of my skinned capsules and they're all around 105pf. The Chinese capsules are much lower at 58pf and 75pf.

It looks suspiciously like the "dead" capacitance (that that is not due to the diaphragm, but rather to the other metallic elements) is way too high.
Since the diaphragm's capacitance is probably about 50pF, it means that the dead capacitance is about equal, which results in a 6dB loss.

 

[gyraf]

105pf is probably too high - this could indicate that

...aaaaand Abbey beat me to it - thanks!

 

[abbey road d enfer]

...aaaaand Abbey beat me to it - thanks!

No competition here

 

[Scrappersa]

That makes a lot of sense. Is that something inherent to the design of the home pattern? Is it the height of the mylar off the back plate? The construction or machining of the backplate? Or the brass material itself?

Just trying to figure out if this is something that can be fixed and/or changed.

 

[abbey road d enfer]

That makes a lot of sense. Is that something inherent to the design of the home pattern?

If you meant hole pattern, definitely no.

Is it the height of the mylar off the back plate? The construction or machining of the backplate? Or the brass material itself?

Without a precise knowledge of the geometry, it is hard to tell, but the ratio of the fixed part of the electrode to the moving part (the actual vibrating diaphragm) is too high.
This the sum of the non moving part of the mylar film and the part that holds it.

Just trying to figure out if this is something that can be fixed and/or changed.

Could probably, but some parts need to be redisigned.
Do you have CAD files?

 

[Scrappersa]

I'll send the CAD file over tonight.

 

[abbey road d enfer]

I'll send the CAD file over tonight.

It's not really visible. What is the distance between the backplane and the ring that clamps the diaphragm? Is it just the thickness of the mylar?

 

[Scrappersa]

The backplane is flat and I'm using shims between it and the mylar. The shims are cut with cricut electric cutter. Total distance should be .002 between the backplane and mylar.

Between the mylar and the clamp (retainer ring), there is nothing.

Order is:
Backplate
.001 shim
.001 shim
Mylar
Retainer ring clamp

 

[abbey road d enfer]

OK, what is the overall diameter and the diaphragm active diameter?
It seems the actual distance between diaphragm and backplate is about 2.5 mil.
Which side is the metallization and what is the diaphragm thickness?

 

[Scrappersa]

Overall diameter of the backplate + delrin is 1.2424 inches. The same size as the diaphragm.

Diaphragm thickness is 5um.

The aluminum side of the diaphragm is facing out away from the backplane towards the outside world.

The brass part of the backplane is .47 inch diameter.

The thickness of the brass retainer ring clamps are .04 inch.

Thickness of the backplane is .246 inches. The brass + delrin backplane were faced off together so they're the same exact height.

 

[abbey road d enfer]

Overall diameter of the backplate + delrin is 1.2424 inches. The same size as the diaphragm.

Diaphragm thickness is 5um.

The aluminum side of the diaphragm is facing out away from the backplane towards the outside world.

The brass part of the backplane is .47 inch diameter.

The thickness of the brass retainer ring clamps are .04 inch.

Thickness of the backplane is .246 inches. The brass + delrin backplane were faced off together so they're the same exact height.

My understanding is that the active part of the diaphragm is only 1/9th of the total area, which represents a loss of nearly 20dB vs. max possible sensitivity.
If your backplate was 1 inch in diameter, the loss would be only ca. 8dB, which would be close to many other capsules.
Maybe I don't understand your description.

 

[Scrappersa]

Hi Abbey,

My mistake. The diameter is .94 inches. I accidentally gave the radius.

 

[abbey road d enfer]

The diameter is .94 inches. I accidentally gave the radius.

Then I'm at loss for an explanation.