Capsule drill patterns and frequency response - where to learn?

[McIrish]

I follow pretty much every capsule thread in the forum. I'm fascinated about the various capsule designs and want to understand better. I don't have any interest in actually making capsules but I'd really like to know more about why they work as they do. Have any of you run across any video or documents that explain LDC capsule design in somewhat simpler terms?

 

[soliloqueen]

grids are usually used because they're easy to mill, but the actual hole pattern is not meaningful in most designs. As long as the volume behind the diaphragm is distributed how you want it distributed (usually evenly) and you've got the resistance where you want it, how you accomplish that is pretty low on the list of factors that affect capsule sound (way below diameter, thickness, chamber anatomy, etc). There's probably a mathematically perfect hole pattern, but I don't think this has ever been pursued because of how little it affects the sound of the capsule compared to the other elements of the design.

 

[McIrish]

Thanks Ari,
Is the difference in sound between a K67 and a K47 due to hole patterns or depth of holes or? Just curious. It makes me wonder how Neumann came up with these patterns. There has to be some math involved. Was the idea to have as much air volume behind the diaphragm without increasing the diaphragm to backplate distance?

 

[soliloqueen]

Is the difference in sound between a K67 and a K47 due to hole patterns or depth of holes or? Just curious.

the biggest difference IMO comes from the fact that the k67 has 2 backplates with space in between and the k47 is one backplate

It makes me wonder how Neumann came up with these patterns.

the k47 is just concentric circles alternating front and rear. the k67 is just a 12 by 12 grid with holes 2mm apart with the holes that don't fit on the electrode surface removed. both very simple patterns. they were chosen because they were easy to draw and remember.

There has to be some math involved.

there's plenty of math involved in the depth, circumference and number of holes!

Was the idea to have as much air volume behind the diaphragm without increasing the diaphragm to backplate distance?

sort of. That's more true in the K87. The point in general is to be able to tailor the behavior of the diaphragm while still keeping a capacitance high enough to get decent signal