Capsule skin doing weird things???

[mkiijam]

I'm pretty new to mic repair, but have a very dirty capsule on a cheap Sterling ST69 that I'm cleaning for practice and fun. It's getting better, but I noticed what I would describe has the Mylar being "sucked in"? It looks to be on just half of the one side and there are little bumps underneath!?!?

 

[GeorgeToledo]

The diaphragm has either lost tension or the polarization voltage is too high. Given the context, it probably lost tension and collapsed.

 

[mkiijam]

What is with the little "bumps" underneath? They literally look like specs of dust underneath the Mylar.

 

[GeorgeToledo]

Usually dust and/or debris from machining the backplate. For the dust, it can be from the environment it was assembled in but in certain cases it can get sucked into the capsule after the fact over time.

If you cleaned it with liquid it can also suck dirt inside if you don’t avoid any openings. With some capsules there can be very small pressure vent holes that are not obvious at first, and the dirt will suck through especially if there is liquid on the surface.

 

[Whoops]

What is with the little "bumps" underneath? They literally look like specs of dust underneath the Mylar.

This, as many others, it's a perfect situation for the old saying:

“A picture is worth a thousand words”