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Author Topic: Capsule Diaphragms: Nickel vs. Gold  (Read 8502 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 »
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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 »

Online 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 »

Offline 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.


Online 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.

Online 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 »

Online 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 »

Online 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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Online 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 »

Online 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.

Offline klaus

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #15 on: March 07, 2018, 08:22:56 pm »
Yes, we all know about that "Chinese Treble". The term should be added to the audio dictionary.
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Offline Piedpiper

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #16 on: March 10, 2018, 12:38:20 pm »
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.

I only listened to one and I heard the same, though they mentioned adding a high shelf on a Pultec, though it's beyond me why they thought that was a good idea. No accounting for taste... I'm hoping to take a visit to their factory which is a couple hours from me sometime if they will allow me to demo it.
row row row your boat...

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Online gtoledo3

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #17 on: March 11, 2018, 05:27:40 am »
It’s supposedly European origin, but who knows.

It makes me wince when a manufacturer wants to sell something for thousands of dollars and has a problem disclosing particulars about tube type or capsule. Don’t be coy, you know? It’s going to come out anyway. In some cases, “I get” protecting tube types, but it’s still annoying IMO. If you don’t tell me what’s in it, I’m not buying!

That mic strikes me as such a poor idea on multiple levels, and from a first time builder at that. Sticking two EF86 or EF86 related tubes in a mic body, and placing the preamp stage IN the mic seems to have “bad idea jeans” written all over it. People are enthused, so there’s that.. Interested to hear one in person nonetheless.

http://www.nbc.com/saturday-night-live/video/bad-idea-jeans/n9937?snl=1


Online Noah Scot Snyder

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Re: Nickel vs. gold sputtering
« Reply #18 on: March 14, 2018, 12:02:31 pm »
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.

On the webpage they say it is " custom handmade premium platinum membrane capsule", so that must mean it's sputtered.

Online Recording Engineer

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #19 on: March 14, 2018, 05:38:37 pm »
I’m going to guess platinum on Mylar (like the couple I previously mentioned), as I’ve yet to see a platinum foil without Mylar any less than 25-microns; maybe they do, I just haven’t seen it yet.

I’d imagine a platinum foil would have to be much, much thinner (maybe somewhere around the 1-1.5 micron range?) to be appropriate for a microphone diaphragm; to make the mass about as typically seen with other metal diaphragms.

Online Recording Engineer

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #20 on: March 14, 2018, 07:40:47 pm »
Ok, found some 0.1-micron platinum, but nothing in between so far. I can only imagine the price too!

Online AusTex64

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #21 on: March 14, 2018, 09:18:09 pm »
The Mastering Lab tube mic was directly coupled to its preamp. Also the Requisite Audio mic has the preamp included in the system. The Chandler mic is not unique in that regard.

Offline Marik

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Re: Nickel vs. gold sputtering
« Reply #22 on: April 13, 2018, 04:36:03 pm »
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.

Mickey,

The layer of deposited gold is in the range of only 100 Angstroms, so it has pretty low conductivity to start with, which is not a priority here, as it is a very high Z circuit, anyway.

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.

Klaus,

The effect of thickness here can be quite deceiving. The density of Ni is 8.9g/cm^3, and of Mylar only 1.38g/cm^3. That means that twice as thick Mylar will still be more than 3 times lighter than Ni counterpart (and more compliant). On the other hand, there will be other factors such as mass of loading air (which is moved along with the diaphragm and which is frequency dependent) and also stiffness of the air trapped between diaphragm and backplate, which works as a spring, effectively damping the diaphragm. Those may (or may not) negate all those mass and compliance differences.

Best, Mark Fouxman
Samar Audio Design
Omni8 Audio
« Last Edit: April 13, 2018, 05:43:47 pm by Marik »
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Offline klaus

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #23 on: April 13, 2018, 06:50:48 pm »
I do to argue with the weight difference between similar-dimensioned nickel and Mylar diaphragms. But your claim that a Mylar film twice as thick as nickel would still be more compliant (i.e.flexible) than nickel is something I would like to see proof of. It does not seem logical.
« Last Edit: April 13, 2018, 08:44:36 pm by klaus »
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Online Kai

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #24 on: April 13, 2018, 07:36:34 pm »
But compliance comparisons...
When building a microphone it's not the goal to have as high tension as possible on the diaphrag. In fact the opposite is true, the lowest tension that still gives a stable result is desirable to extend the low frequency response.
I once talked to Mr. Wutke from Schoeps here in Karlsruhe, and he told me that is what they do with their figure of eight and cardiod capsules. Omnis are different.
Metal could have a point over Mylar in long-term stability in that regard, but I'm only (educated) guessing here.

Offline Marik

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #25 on: April 16, 2018, 02:49:26 pm »
But your claim that a Mylar film twice as thick as nickel would still be more compliant (i.e.flexible) than nickel is something I would like to see proof of. It does not seem logical.

Klaus,

The Young's modulus (i.e. a measure of the stiffness) for Ni is 190x10^6 PSI and for Mylar 1x10^6 PSI. In other words, Mylar is by far more compliant material.

When building a microphone it's not the goal to have as high tension as possible on the diaphrag. In fact the opposite is true, the lowest tension that still gives a stable result is desirable to extend the low frequency response.

Kai,

But with lower tension then you are losing top end response. The carefully chosen optimum tension/tuning frequency for a given capsule is always a part of a system comprised of capsule acoustical chamber parameters, time delay network, resonator system (if any), and desired voicing. It will also affect capsule's sensitivity.

Best, Mark Fouxman
Samar Audio Design
Omni8 Audio
Mark Fouxman
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Online Kai

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #26 on: April 16, 2018, 05:24:54 pm »
But with lower tension then you are losing top end response.
In fact you linearize the bass.
Using as low tension as possible is a quote from Schoeps's chief engineer Mr. Wutke with whoom I had close contact. I even tested a prototype mic for them at that time. Schoeps is located in my hometown.

Specially on fig. of eight mic's the low frequency response is of major concern, as the pressure gradient (the pressure difference between front and backside of the capsule / diaphrag) gets lower with frequency.
The stiffer the diaphrag the less it will follow the air movement.
Most REAL (single diaphragm, not double-cardiod) fig. of eight condensors roll off below 200Hz or even higher because of this.

Schoeps CCM8 reaches 50Hz with a soft rolloff to only -6dB (often compensated by the proximity effect when used as spot mic). There is no problem in the high range with this mic, it's ruler flat up to 15kHz and sounds very nice and rounded.
The mic uses mylar sputtered with gold, but in former times Schoeps built mic's with pure nickel diaphragms with comparable accoustic properties.

You are right with cardiods, they present a complex system using a combination of even more then the mentioned accoustic effects, needing to be properly tuned to each other.
Still, low tension is desirable here if you need to cover the full range.
Klaus prefers the lower tensioned specimen of the Neumann capsules e.g., for their fuller bodied sound.

This low tension close to the possible is one of the main reasons for cardiod capsule failure, there is no big margin like with higher tensioned omnis.
« Last Edit: April 16, 2018, 05:50:48 pm by Kai »

Offline Marik

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Re: Capsule Diaphragms: Nickel vs. Gold
« Reply #27 on: April 16, 2018, 08:15:07 pm »
Using as low tension as possible is a quote from Schoeps's chief engineer Mr. Wutke with whoom I had close contact. I even tested a prototype mic for them at that time. Schoeps is located in my hometown.

Kai,

As always, the evil is in details. In order to compensate for high frequency loss (as a result of diaphragm' lower tension) Schoeps uses resonator system, which is just another way of implementing and making it work...


Specially on fig. of eight mic's the low frequency response is of major concern, as the pressure gradient (the pressure difference between front and backside of the capsule / diaphrag) gets lower with frequency.
The stiffer the diaphrag the less it will follow the air movement.
Most REAL (single diaphragm, not double-cardiod) fig. of eight condensors roll off below 200Hz or even higher because of this.

The single diaphragm fig8 condenser is very specialized capsule and there were only a few more or less successful models on the market. Of course, I was talking about cardioid capsules.

In general, to make a fig8 single diaphragm we need a mass controlled system, so the diaphragm is tuned to a very low frequency. In this case the sensitivity will drop with rate of 6dB per octave going up. On the other hand, the pressure gradient forces on the diaphragm will increase twice per each octave. That's how we will get a linear frequency response. That's why ribbon microphones naturally have a linear response up to the point of cancellation on the top extreme, where the front to back distance is equal to the frequency of wave length and pressure gradient is 360 degree out of phase.

Condenser single diaphragm works as mass controlled only above the frequency of tuning resonance. Below it is a resistance controlled system. In order to make a flat response we need to introduce acoustical resistance. The lower the tuning resonance, the less acoustical resistance we need, the more output such capsule will have for a given linearity. But of course, as you rightly mentioned, here we are faced with diaphragm stability problems, which is the main limiting factor.

Quote
You are right with cardiods, they present a complex system using a combination of even more then the mentioned accoustic effects, needing to be properly tuned to each other.
Still, low tension is desirable here if you need to cover the full range.
Klaus prefers the lower tensioned specimen of the Neumann capsules e.g., for their fuller bodied sound.

This low tension close to the possible is one of the main reasons for cardiod capsule failure, there is no big margin like with higher tensioned omnis.

As I mentioned before, the diaphragm tensioning depends on the desired voicing and very much depends on entire system it is part of. In general, all the capsules are tuned differently. For example K47 is considerably low, K67 quite a bit higher. On the other hand, CK12 way higher than either. The reason being the first two are aperiodic designs and introduce quite high acoustical resistance and damping to the diaphragm, while the CK12 is a multi-chambered and rather resonant system.

Best, M
« Last Edit: April 17, 2018, 04:25:26 pm by Marik »
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