Paul Dorman wrote:
This video claims that "cutting the electrode is perhaps the most
difficult part of making a capsule":
https://www.youtube.com/watch?v=V-i0GztOrlg
They claim the process requires a lathe of 2 microns flatness
accuracy. Another Soyuz video says that some lathes can get down to
1-2 microns accuracy.
Yes. You don't really need to get it that accurate because it will be
lapped, but the better you get it, the easier and faster the lapping
process is.
The video shows that they further hand-polish the electrodes on a
"special surface", and then they measure the flatness with an old Soviet
micrometer, which measures down to 1 micron.
Yes, this is called lapping.
They only need to get it down to about a micron because of the way the
capsule is designed; there is no need to balance two halves perfectly
to make a figure-8 pattern work like there is with the U87. From the
standpoint of manufacturability, this is a much better capsule than the
K87.
500 angstroms is 0.05 microns. How are they supposed to measure
down to 1/20th of a micron? And would it even matter?
In the old days, people used optical flats. These days we use an
interferometer. Cheap semiconductor lasers have made this a very easy
method to measure the backplate accuracy and flatness, as well as to
measure the diaphragm flatness once it's in place.
Have you ever cut your own electrode? Do you have access to a
2 micron accurate lathe?
I have certainly cut hundreds of backplates and stators over the years.
Sadly, the runout on my lathe is not within 2 microns, though, which
makes the lapping a pain.
It's very easy to make a microphone capsule, it's very hard to make a good
one.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."