[Scott Dorsey]

Paul Dorman wrote:
On 12/29/2020 11:35 AM, Scott Dorsey wrote:
And I don't see anything too special here, really. Assuming
they use torque wrenches for the ring that mounts the plastic
membrane, it looks like any assembler could do it.

No, you're at least two orders of magnitude off. However, that's how the
Chinese guys do it.

There are two things they will not show you:

1. How the backplate is made optically flat and parallel to the diaphragm.

The flatness of the backplate will depend on the lathe that it is
cut with.

Umm... no. It's flat. Not mils flat, not microns flat. It's hundreds of
angstroms flat. It's flat enough that you put the plate on it and you
don't see any Newton's rings. It is cut, yes, but then it's lapped and
then sometimes a third process is used to make it still flatter.

More than that, it's absolutely parallel to the diaphragm. This turns out
to be hard to do because it relies on more than just the stator being
flat.

If you don't get these right, your null in figure-8 mode turns to crap
because you can't balance the two halves of the capsule properly.

Capsule construction is not rocket science.

Most of it isn't. I can make a serviceable K87-style capsule with a decent
null, after a good bit of practice. Making a KM84 capsule is a lot harder.
But you look at the more modern pop-together designs and it's impossible to
do any of those by hand.

I suggest you try it. I thought it would be a lot easier than it is.
Start with an M7 because it's definitely the easiest one to tension on
a trampoline and you can do it mostly with jeweler's tools. You'll need
to make custom jigs to drill the backplate but Neumann did something very
smart to make it easy to lap it on a hand machine.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."