M50 aluminum membranes

[Marik]

Well I know that the nickel capsule was 0.8 micron but the aluminum diaphragm that came on my M50 capsule mounted on my MM2 measure a whopping 60microns thick which I cannot understand.

Tim,

Is it a bare Al, or deposited on some kind of film subtract? In general, Al is very mild, compliant, and easily 'remembers' the shape if stretched, so it is very hard to tune it, unless it is fairly thick (or deposited on a film). Much thinner Ni, Ti, or Stainless Steel are much easier to deal with.

The other consideration, in the omnies the stiffness is much more important than weight—hence we want to stretch it to the top of the bandwidth. For example for that reason Altec 21B diaphragm was laminated from silicon and silica of some 30um thickness (and not stretched at all). So that 60um doesn't surprise me.

Best, M

 

[Murdock]

I’ve suspected it being Duralumin for quite some time. I’ve been interested in finding out the true thickness used for a long time. I’ve read 0.8-microns turned super-duper tight and with a 83pf measurement. Everyone has said that’s impossible; must be 8-microns. It seems no one knows for sure. Someone must know though!

8 micron is what Neumann state themselves... there are documents about it. I don’t know where this 0.8 micron comes from. Probably from people who think „no, that can‘t be. The thinner the better. And an icon as the M50 has to be as hifi as possible“.

 

[Tim Campbell]

Thank you all for your help. 8 micron aluminum is easy to get so I think I will try that and tune as high as possible (20,000 -40,000hz has been stated other places for omnis ) measure it and see what the frequency response looks like.

 

[Murdock]

I would be intersted how high you can tension the 8 micron aluminum before it breaks.
The resonance frequency of the whole capsule will be way different than the resonance frequency of the membrane itself. But you probably already know that. I once read that most diaphragmes can't be tensioned to more than 7 to 8Khz. The cavities and air behind the membrane shift the resonance up. But that was in an old book. So I don't know how new materials react to high tension.

 

[k brown]

Is anything like Duralumin still available?

 

[Gus]

Did some searches
Pure is in 1000 series so maybe 1145 or 1199 Aluminium alloy - Wikipedia
Duralumin is 2000 series
Close would be 60u or .002"(60u is .0023") shim stock of pure or alloy
Maybe the disk is not installed and tensioned but premade and installed like the Altec Marik posted about
Maybe the stiffness is set by the thickness
It looks like mounting holes in the disk was "punched out" as well as the outside edge from the picture.
I think this would need some tooling to be made to do this cleanly

more to read
https://www.tab-funkenwerk.org/history-of-tfk/the-original-47/https://www.coutant.org/we47/index.html

 

[GeorgeToledo]

I have notes that the aluminum for K53 was rolled to the desired thickness and then lacquered.

I think the claim that the K53 had a thicker diaphragm, like what we see here or close, may pan out to be true. The TLM150 capsule had a 2.5 micron diaphragm with otherwise similar specs, same distance to backplate, etc. Since nickel is heavier than aluminum, it suggests that the aluminum would have been greater than 2.5 micron, not less.

 

[Recording Engineer]

8 micron is what Neumann state themselves... there are documents about it.

So people say, but don’t produce any of the documents. I still haven’t seen any. Well, that’s not true. The very one time someone did, it wasn’t clear. If I recall correctly, it was sort of a in-depth run-down on a few mics; sorta like a very long-winded answer to an interview question, but not an interview at all. Read it one way and you think “Oh, it’s clear as day right there”. Read it another way and you’re like “Wait a minute, that’s not clear at all, they very easily could be talking about this not that.”

 

[Ericbazaar]

This is an very early M50 (if i remember correctly Serial No #009), early K50 Capsules were made of gold sputtered Foil. View attachment 116666

 

[soliloqueen]

Duralum corrodes. Did they sputter the gold onto the duralum?. That would be nuts. Or maybe this is a re-skin or something

 

[k brown]

According to this, the first version of the M50 capsule was gold-spttered PVC, not metal foil.

http://www.saturn-sound.com/Curio's/neumann's kk50 - early type k50 capsule.htm

 

[Ericbazaar]

I read that the first version of the M50 capsules were gold-spttered PVC, not metal foil.

http://www.saturn-sound.com/Curio's/neumann's kk50 - early type k50 capsule.htm

The M50 was never developed by Neumann it was founded by the NWDR called B-M49 and B-M50. Maybe the first K50 were made by the NWDR. Neumann got later the license to built the M49 and M50, they changed the Foil to metal and changed the diameter of the capsule as well.

 

[GeorgeToledo]

There’s an AES paper by Neumann’s Martin Schneider that confirms the NWDR origins of the M50 capsule…though it is also confirmed via articles from that time.

http://recordinghacks.com/pdf/neumann/omni_sphere_aes_schneider.pdf

 

[GeorgeToledo]

Maybe lacquering the aluminum was an idea to prevent corrosion.

(Though I haven’t seen specific reference to duralum myself. Definitely aware of it corroding.)

They apparently changed to aluminum because the PVC couldn’t handle the high tension they wanted to use.

 

[Tim Campbell]

If they laquered the membrane I would guess it would have been on the backplate side to prevent shorts. Shorts burning holes in metal membranes can be seen famously on KM54/56 capsules

 

[Recording Engineer]

Klaus Heyne’s comments on the subject:
https://repforums.prosoundweb.com/index.php/topic,37137.msg536840.html#msg536840
So far, what we know for sure about the aluminum version of the kk53 is that there was 10-microns between the diaphragm and backplate and there was no insulation between.

 

[GeorgeToledo]

My comments about the rolling to thickness and lacquering originated from Neumann, and their old pinboard. As did the point about them having to make the original nickel diaphragm of the TLM50 thinner because nickel weighs more.

 

[bockaudio]

K Brown this is the earliest version of the M50 capsule. Neumann produced it from 1948 -52. This is a Neumann MM2 microphone built for anechoic chambers. Only 90 of them were ever built. Mine is no.50

The earliest M50 were gold on pvc.

 

[Murdock]

So people say, but don’t produce any of the documents. I still haven’t seen any. Well, that’s not true. The very one time someone did, it wasn’t clear. If I recall correctly, it was sort of a in-depth run-down on a few mics; sorta like a very long-winded answer to an interview question, but not an interview at all. Read it one way and you think “Oh, it’s clear as day right there”. Read it another way and you’re like “Wait a minute, that’s not clear at all, they very easily could be talking about this not that.”

You can clearly read it here on page 3:
https://manualzz.com/doc/3341055/neumann.berlin-pressure-microphone-with-sperical-acoustic

 

[Recording Engineer]

You can clearly read it here on page 3:
https://manualzz.com/doc/3341055/neumann.berlin-pressure-microphone-with-sperical-acoustic

I see. Thank you. But clearly? Most definitely not for me.

In fact, the more and more and more I read that whole The Archtype section on page 3 (where 8-microns is mentioned), the more and more and more I’m pretty darn positive it’s speaking specifically of the TLM 50. That whole section is about the TLM 50, even though it starts with “At the beginning of the Fifties…”Anyone know for sure how thick the nickel diaphragm in the TLM 50 is? In addition, in the same paragraph where 8-micron is mentioned, it boasts about low noise, as if something new has been achieved, like in this 2-year-old (at the time of this paper) TLM 50.

On the other hand, as I continue reading on to page 5, I answer my own question on the TLM 50 nickel thickness and my pretty darn sureness goes away completely as it then mentions ultimately deciding on 2.25-microns for the diaphragm for the TLM 50 (I think); which makes sense for nickel. Plus, GeorgeToledo’s link confirms it.

So this leaves me open to the possibility, as much as anything else, that 8-microns is correct for the aluminum diaphragm in the kk53, but nothing for sure.

This is haziness, not clarity, and continually spins me. It’s a problem of mine. Ha!