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Author Topic: Capsule Diaphragms: Nickel vs. Gold  (Read 9200 times)

Offline Mickeyrouse

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Capsule Diaphragms: Nickel vs. Gold
« on: February 25, 2018, 09:32:56 am »
Though I have been around mics a long time, only in the last few years have I learned about Neumann’s nickel membranes.
What are the comparative characteristics of one versus the other? If they perform the way some posters seem to imply, why did Neumann discontinue them? Did anyone else ( Schoeps, B&K, Neumann Gefell, etc) experiment with them?
  It seems like nickel, at a higher melting point and a higher Brinnel hardness, would be more difficult to work with. And I can’t imagine a better conductor than gold. Since so little gold is actually deposited on a membrane,  it doesn’t seem like raw material cost would be significant. Judging by some comments here and on other bulletin boards, the longevity of the membranes doesn’t seem to compare to more commonly used materials, though that may be unrelated to the metal used in sputtering. And it seems like the nickel membrane surface would be more likely to suffer corrosion fron vocalist’  saliva aerosols.
    Inquiring minds want to know.
« Last Edit: February 26, 2018, 07:15:57 pm by klaus »

Offline klaus

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Re: Nickel vs. gold sputtering
« Reply #1 on: February 25, 2018, 06:41:56 pm »
Among speculation why metal diaphragms are not more prominent in capsule manufacturing today (material sourcing problems, lack of manufacturing and assembly skills, long-term thermal stability or stability when momentarily exposed to environmental stresses, etc.) one fact is incontrovertible:

When a micron-thin diaphragm makes contact with an electrically charged backplate, as occasionally happens when high sound pressure or popping occurs, arcing results, which can burn holes into the diaphragm. You can prevent this only by coating the metal diaphragm with an insulating layer. But that may defeat the purpose of using a very thin and agile metal diaphragm instead of a plastic one that usually is twice as thick or thicker than a metal diaphragm.

The other way to prevent arcing would be to put an isolation layer on the backplate. I am not sure who did or does that, but there must be a good reason why this technique is not broadly applied.
« Last Edit: February 26, 2018, 03:04:19 am by klaus »
Klaus Heyne
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Online David Satz

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Re: Nickel vs. gold sputtering
« Reply #2 on: February 26, 2018, 12:34:41 am »
Before tensilized Mylar became available in the mid/late 1950s, Schoeps used nickel diaphragms in all their capsules (e.g. the M 221 series). But all the Western European manufacturers changed over to Mylar as soon as they could, because the resulting capsules are that much less fragile.

At Schoeps after the changeover, whenever any older capsule needed a repair that called for a new diaphragm, they installed a Mylar membrane in place of the nickel one. At one time I owned a pair of M 221 B microphones, and one of my M 934 B capsules underwent this change. After I got the capsule back from repair I made several recordings with the pair before it ever occurred to me that now the two diaphragms must be of different material from one another. I couldn't hear any difference between them, at least in the cardioid setting of the capsules.

All in all, diaphragm material (and also diaphragm thickness) as aspects of a capsule's acoustical design strike me as relatively minor factors in the sound of a microphone, as long as they're within the parameters required by the capsule's acoustic design. A membrane's excursions in response to sound are so tiny, the mass of the diaphragm is swamped by the mass of the air that has to move along with it, and the motion of the air on the backplate side of the diaphragm is constrained by the carefully controlled internal friction within and between the chambers of the capsule. The diaphragm isn't an independent "actor" by any means.
« Last Edit: February 27, 2018, 09:02:49 am by David Satz »

Offline Kai

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Re: Nickel vs. gold sputtering
« Reply #3 on: February 26, 2018, 04:22:54 am »
... though that may be unrelated to the metal used in sputtering.
Nickel membranes are not sputtered on Mylar film like it's done with gold, but are solid metal.

Nickel is still indispensable in measurement microphones, because it allows constructing microphones that do much less change their sensitivity with temperature, and having a much greater temperature range they can survive.

If you heat up a mylar diaphragma it loses its tension (even permanent from some temperature point on) and comes closer to the backplate, thus increasing the mic's sensitivity.

Same would apply by some lesser amount to Nickel due to thermic expansion only (opposed to Mylar's material characteristic change), but as the capsules body is built from metal too, this is largely compensated. Permanent changes due to temperature are avoided by pre-aging the capsules in an oven at temperatures a mylar capsule would not survive at all.

For a measurement microphone it's important to be extremely parameter stable over temperature and time, something that cannot be achieved with Mylar.
So if you have a cheap electret measurement microphone, you better not put it out into the sun.
« Last Edit: February 26, 2018, 04:30:35 am by Kai »

Online soapfoot

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Re: Nickel vs. gold sputtering
« Reply #4 on: February 26, 2018, 10:04:48 am »
And I can’t imagine a better conductor than gold.

Silver and copper are both superior conductors to gold.

Those three, plus aluminum and zinc, are all superior conductors to nickel.


Offline Jim Williams

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Re: Nickel vs. gold sputtering
« Reply #5 on: February 26, 2018, 12:31:52 pm »
Gold was selected because it resists any form of corrosion. Silver could possible work better if it didn't oxidize. Platinum also might be a good choice but I never heard of anyone trying it.

Offline klaus

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Re: Nickel vs. gold sputtering
« Reply #6 on: February 26, 2018, 12:32:18 pm »
(...) If you heat up a mylar diaphragm it loses its tension (even permanent from some temperature point on) and comes closer to the backplate, thus increasing the mic's sensitivity.

Pretty sure that's wrong. A Mylar film will actually tighten up with the application of heat. One of the first experiments I made to lower some over-tensioned Neumann membranes was to apply heat, and the diaphragm's tension got tighter, not looser.

In support of this theory: drum shops remove dents in Mylar drum heads by aiming a heat gun on the dent, until it disappears. And it won't come back, so membrane tensioning through heat treatment is permanent.
« Last Edit: February 26, 2018, 04:12:45 pm by klaus »
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Offline Mickeyrouse

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Re: Nickel vs. gold sputtering
« Reply #7 on: February 26, 2018, 02:30:22 pm »
That’s what’s great about this forum: access to a lot of truly knowledgeable people.

Online Recording Engineer

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Re: Nickel vs. gold sputtering
« Reply #8 on: February 26, 2018, 03:54:12 pm »
Platinum also might be a good choice but I never heard of anyone trying it.

Allen Luke at Luke Audio uses platinum. I’ve heard it in his AL-X751 and his 67-style capsule in a Schoeps-style circuit. I own his AL-Y56 where all 3 capsules use platinum, and I have a pair of Barbaric Amplification mics, inspired by conversations I had with Stephen Paul on what he liked to do with C12s, a couple years prior to his passing. They use Tim Campbell CT-12 capsules, but reskinned by Luke Audio with 1-micron Mylar and platinum.

If I recall correctly, I’m pretty sure Shannon Rhoades at Mic Rehab uses or has used platinum too.

Offline Kai

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Re: Nickel vs. gold sputtering
« Reply #9 on: February 26, 2018, 05:40:40 pm »
Pretty sure that's wrong. A Mylar film will actually tighten up with the application of heat.
Ok, my experience comes from electrostatic headphones drivers, which might have much higher tension then microphones (see below).
Still, for a measurement microphone either higher or lower, permanent or temporary change would be bad.
This might be the reason that they all use Nickel.
Bruel&Kjaer gives reliability figures in centuries, based on extrapolation of climat chamber experiments.
Of coarse that's hard to prove in reality, in my experience it's more like several decades, and they die from bad things happening inside, the diaphragma still in perfect condition.
When I open them up I find visible backplate corrosion.

Add:
There is a difference between cardioid and omni capsules:
Cardioid (and fig. of eight) capsules are tensioned as low as possible while maintaining stability, to extend the low frequency response.
Omnis use a higher tension.

Regarding conductivity:
The amount of conductivity is of no concern. Every metal is by far more than sufficiently conductive for microphone purpose.
If you bias the diaphragma and use the audio signal from the backplate, it's not even necessary for the diaphragma to conduct very good. It's only the biasing charge that matters in that case, and this builds up even if the diaphragma has extremly low conductivity (but at least it needs some).
No current flows through the diaphragma in that case.
With electrets (but not with back electrets) you have exactly that case: no conductivity at all on the diaphragma, instead extremely high isolation and a fixed charge.
« Last Edit: February 27, 2018, 06:28:13 am by Kai »

Offline AusTex64

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #10 on: February 26, 2018, 08:25:26 pm »
Klaus wrote: "The other way to prevent arcing would be to put an isolation layer on the backplate. I am not sure who did or does that, but there must be a good reason why this technique is not broadly applied."

Microtech Gefell coats the backplate on their M294/295 capsules with Teflon to avoid the arcing pinholes.
« Last Edit: March 06, 2018, 01:55:19 pm by klaus »

Offline Noah Scot Snyder

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Re: Nickel vs. gold sputtering
« Reply #11 on: March 06, 2018, 11:45:54 am »
Gold was selected because it resists any form of corrosion. Silver could possible work better if it didn't oxidize. Platinum also might be a good choice but I never heard of anyone trying it.

The Chandler REDD mics have platinum capsules.

Offline klaus

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #12 on: March 06, 2018, 01:59:18 pm »
So, the Chinese are now able to makle a large platinum diaphragm that sounds good and lasts? Would love to hear that mic.
Klaus Heyne
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Offline Kai

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Re: Nickel vs. gold sputtering
« Reply #13 on: March 07, 2018, 05:47:48 pm »
The Chandler REDD mics have platinum capsules.
I don't find it mentioned on the manufacturers website if it's platinum sputtered on (mylar) foil or a massive platinum diaphragm.
I suspect it's sputtered, so this would not be so special as it doesn't matter what type of metal is used for the process.
I don't think it's possible to tension a pure platinum diaphragm enough to make it work.
The advantage of platinum versus gold is its higher resilience against corrosion.
Let's have a look on it again after 50 years of use :)

BTW:  it seems there is still a misconception about the necessity of low resistance for the coating (silver proposal) - any metal is by far conductive enough to do the job.
« Last Edit: March 07, 2018, 08:21:20 pm by klaus »

Offline Kai

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #14 on: March 07, 2018, 06:42:41 pm »
So, the Chinese are now able to makle a large platinum diaphragm that sounds good and lasts? Would love to hear that mic.
I listened to the advertised recordings and both have some "chinese treble" in common.
If it's the mic or anything else in the recording chain I can't decide.