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Boner
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2nd November 2009
Old 2nd November 2009
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Ribbon Mic Material

Lately I've seen some manufacturers say they use NOS RCA ribbon material in their mics. Anyone know the difference between NOS RCA material and "regular"
ribbon material? It would seem to me that aluminum is well, aluminum.

Also, does the number of corrugations per inch and width of the ribbon affect the sound dramatically?

Thanks.....Lee.
Les
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2nd November 2009
Old 2nd November 2009
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AEA uses NOS RCA material from the '70s. It is reported to be 1.8 micron pure aluminum.

Many modern mics use 6 micron.

There could be differences in the degree of cold working/heat treating with different materials, particularly if they were alloys. Some old mic claimed to use duralumin, a high strength alloy that would greatly enhance durability of the ribbon. I have been told that the high strength alloys are almost impossible to roll to such thicknesses. I needed such a material for an industrial ultrasonic microphone. I could only get low alloy(almost pure aluminum) foils. No one I contacted could create high strength foils below 100 microns or so. Too bad. Some have ten times the strength of pure aluminum, while retaining good conductivity.

I think it was Coles/BBC that claimed to "hammer" ribbon material to improve it's strength properties from further cold working, but know no details.

As far as Width and corrugation design...yeah, I would say it matters alot, particularly in the 6 micron stuff.

Making or reribboning some mics?
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2nd November 2009
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3rd November 2009
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Corrugations, width, length and thickness really do matter. All aluminum is not the same aluminum. Careful viewing under a microscope can show ribbon flaws, tiny holes, rips etc. So having a high quality material is important. I think most ribbon mics out there are in the 2 micron range. Royer has released some mics with thicker ribbons, but I do not think they are 6 micron. The normal royers are 1.8 or 2.5 and Live ones go up to 4 micron max.

I am pretty sure most ribbon material for mics is beaten to thickness, not rolled.
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3rd November 2009
Old 3rd November 2009
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Paul, I guess you guys have enough NOS rca stuff to last forever.

As I researched foils for the ultrasonic microphones I designed I found foil rolling was typically done in two layers. That's why kitchen type foil has a glossy and matte side. The latter surface was the inside part of the sandwich. Does the old RCA stuff look like that?

I imagine more than two layers could be used. Then both sides might be matte on the inside layers.

Of course thin Al foils can be sputtered or evaporated...done all the time in integrated circuits. The crystalline structure tends to be collumnar though, resulting in a weak brittle film compared to wrought material.

As far as hammer beating the foil it seems there would be tell tale marks left on the surface finish. See any of that?

As far as 6 micron...well that's second hand information from some chinese mics. I haven't personally measured them.

The only heat treatable AL foil I managed to get was 6063. But nowhere near 2 micron. I ended up using a maraging steel foil anyway...ten times the strength of pure aluminum. This was for formed diaphragm domes though, not ribbons.

I still wonder if high alloy heat treatable aluminum couldn't be hot rolled or something. We did hot rolling and forming of beryllium foil with good success at Shure.

A precipitation hardened 2000 series aluminum foil would dramatically increase ribbon durability.

Might have corrosion issues though. In aircraft use it's flashed with a thin
surface of pure aluminum.

There's also a patent for gold flashing microphone ribbons, but I think it's a bad deal. Gold and aluminum form a brittle poorly conducting AlAu2 compound called "purple plague".
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3rd November 2009
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Quote:
Originally Posted by Les View Post

I imagine more than two layers could be used. Then both sides might be matte on the inside layers.

Of course thin Al foils can be sputtered or evaporated...done all the time in integrated circuits. The crystalline structure tends to be collumnar though, resulting in a weak brittle film compared to wrought material.
Hi Les,

In addition, the sputtered Al has worse conductivity, so the ribbon's DCR will be higher.

Quote:
Originally Posted by Les View Post

I ended up using a maraging steel foil anyway...ten times the strength of pure aluminum. This was for formed diaphragm domes though, not ribbons.
That won't work with ribbons. It is way too heavy (the density about 3 times higher than Al), and has low compliance.

Best, M
Boner
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3rd November 2009
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Thanks Les, Michael and Paul (sounds like an old Folk group). I'm really getting and education. I would assume then that width, currugations etc. would would affect tone and volume?
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3rd November 2009
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Quote:
That won't work with ribbons. It is way too heavy (the density about 3 times higher than Al), and has low compliance.
Right...it was for very high power microphones for energy harvesting in ultra high sound fields... 10^5 Pascal. So fatigue strength was the main issue.

Resistivity density product is the magic number for voice coils and ribbons. Aluminum and the alkalai earth metals are best. (the later unfortunately catches on fire!)

You can see I have been researching ribbon stuff pretty heavily. We still haven't had that talk...

One big issue with thin High strength Al foils seems to be alloy element precipitation in the inter and final anneals. 8000 series aluminum (AL/FE)
works though.

Also I wonder if the ribbon mic foils had the usual final anneal to "dead fold" condition as most other Al foils are. I think that would be bad...and a good reason to have to beat it further to work harden.

One might think dead fold soft would have better damping...but I think not. To do so would mean it's in plastic deformation, causing rapid fatigue,loss of tuning, etc.

Lee, you have some pretty serious microphone people crawling out of the woodwork on your thread. Hope you don't mind. We usually talk about this stuff elsewhere...
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3rd November 2009
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Quote:
Lee, you have some pretty serious microphone people crawling out of the woodwork on your thread. Hope you don't mind. We usually talk about this stuff elsewhere...
I don't mind at all Les. Discussions like this benefit us all. I just find it a little funny that all I wanted to do was get some basic information so I could attempt to reribbon and old Shiny Box 46 a friend gave me! Please continue...............
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3rd November 2009
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Lee, go to prodigy pro lab forum and click on the meta link. Lots of DIY ribbon stuff there. Marik has made a lot of great posts there. You'll find out what you want to know.
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4th November 2009
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Quote:
Lee, go to prodigy pro lab forum and click on the meta link. Lots of DIY ribbon stuff there. Marik has made a lot of great posts there. You'll find out what you want to know.
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Thanks for the tip Les. I figure I got the mic for nothing so I'll experiment with reribboning it and maybe adding a lundahl transformer. When it comes to electronics I'm pretty much clueless, but hey, it can't sound any worse than it does now!

Thanks again......Lee.
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5th November 2009
Old 5th November 2009
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Quote:
Originally Posted by Les View Post

One big issue with thin High strength Al foils seems to be alloy element precipitation in the inter and final anneals. 8000 series aluminum (AL/FE)
works though.

Also I wonder if the ribbon mic foils had the usual final anneal to "dead fold" condition as most other Al foils are. I think that would be bad...and a good reason to have to beat it further to work harden.

One might think dead fold soft would have better damping...but I think not. To do so would mean it's in plastic deformation, causing rapid fatigue,loss of tuning, etc.
Hello Les,

I did not study materials and most of my knowledge in that field comes from conversations with my foil manufacturer/supplier and microphone textbooks, which of course, do not give in-depth information.

The main requirements for the foil are high conductance, low density, high compliance, and longevity, but I am sure you know that. From what I gathered the best compromise to answer all is at least 99% pure Al. The alloys usually compromise some of that. A good example is Duralum, which was used a lot some decades ago. It had high strength, but suffered from low compliance and also was prone to oxidazing. All the Duralum ribbons from 40's-70s I was working on were extremely stiff and brittle, as a result of that oxidation.

But again, if you are good with materials I would be more than happy rather to listen...

Quote:
Originally Posted by Boner View Post
I don't mind at all Les. Discussions like this benefit us all. I just find it a little funny that all I wanted to do was get some basic information so I could attempt to reribbon and old Shiny Box 46 a friend gave me! Please continue...............
Lee,

If you want your mic to be up to specs and in a good working order, may I suggest you contacting Jon (from Shiny Box), first. He is a cool guy and has an excellent customer support:

Shinybox Ribbon Microphones

Best, M
Les
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5th November 2009
Old 5th November 2009
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Quote:
But again, if you are good with materials I would be more than happy rather to listen...
Heh, well by education i'm an aero engineer, so yes I had a good bit of materials study.

But with this last microphone project it got so critical that I had to hire a metallurgist. Spent a ton of money. We did a lot of tests on aluminum, beryllium, titanium and other foils. But it was for diaphragms, not conducting elements.

However we studied electrical conductivity because it was a means to evaluate precipitation hardening mechanisms in the copper aluminum hardenable alloys. Turns out it can be almost (not quite) as good as pure Al with some age hardining mechanisms.

The tensile and bending modulus (therefore compliance) is actually about the same for the hardened cu/al and the pure al. It's just that the former is much stronger.
BUT
Not when it corrodes. And it's prone to that. Then the foils get brittle, as you said. So It has to be protected. It's a BIG issue for me, because I'm a pilot. You better believe I closely inspect hardened aluminum wing spars and structures before I fly an old vintage plane. Life or death!

I'm just looking to see if there is any incremental, meaningful improvement left that could be done to ribbon microphones. You see, I have lately designed a ribbon specific mic preamp, and want to look at possible microphones as a product too.

As a microphone/electronics designer (usually ultrasonic) I'm totally familiar with the usual tricks and trade offs with ribbons. Resonator and diffractor plates, baffles, magnetic circuit, transformers, all of that.

I used to make ribbon mics as a teenager from Wrigley's gum foil after reading Harry Olsons stuff. Shocked to see others did that too.

My dad had a job with Western Electric while he was in college in the '40s
and he was the ribbon tuning technician for the 639!!

But I wonder if anything else could be done. I guess one of the last things was the roswellite stuff, and I note that my old alma mater Shure is selling those C&T mics. Seems very durable, but a composite ribbon has got to have some sensitiviy tradeoffs. A hardened Al might have the durability with little tradeoff, if it had a few nanometers of something to protect it from degradation.

Just thinkin out loud...
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6th November 2009
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I think when I say foil for ribbons I really want to think of it as aluminum leaf. It really is beaten, just like gold leaf, to get it that thin. Not directly on the metal but through some other materials.
I had never heard of maraging steel, i guess its used in aerospace, but what are the magnetic properties? We use some pretty high powered magnets right at the gap where the ribbon is suspended.
As far as I know the only material used for ribbon mics is aluminum except that new stuff shure now has from C+T. I think C+T are the only people who moved away from aluminum, partly because they were tied into another company with good research in other fields. Metallurgy and materials study can rack up a lot of cost in design work and there are not many people in that part of ribbon mic business. None of those Chinese mic companies/importers spend money on serious R&D. So I think yes there are some good possibilities, but we know what works and it works well. Wes always thinks about these type of things.
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6th November 2009
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Hi again Paul.

The "maraging steel" alloys again are not suited for conductive applications where resistivity density product is important. We used it in special microphone diaphragms in unusual enviroments where the sound is so powerful it can cause burns. (supersonic shock waves)

Maraging basically refers to materials that have dual hardening mechanisms... martensite transformation (the mar part) and age hardening by precipitation of intermetallics (the age part). They are among the highest fatigue strength aerospace metals on the planet.

The heat treatable aluminums strengthen by precipitation only, but have good resistivity density products if you can keep them from rotting. Well, with the right heat treat.

Research stuff like this usually gets better funding than audio, I know. Back in the hifi boom days Shure let me just sit around and do math for a little while at least. Not like that now.

Now I turn my attention for a bit to ribbon microphones. I can't say I can offer any real, significant improvement in this 75+ year old technology. I'm just thinking about it. And I can use the technology we have learned from well funded military/industrial reasearch we do if it helps. A lot of that is materials technology.

I know Wes thinks a lot about this too. You guys have done a super job promoting the old ribbon mics. I think they were the first truly high fidelity
recording instruments, even considering the early condensers. Their smooth predictable off axis response still offers great benefit even in the 24 bit+ digital age. We have tamed preamp input stage voltage and current noise to the point the ribbons can offer very good dynamic range.

Anyway, right now I'm thinking mostly about durability and blast resistance of the ribbon. C&T use a composite polymer to add substantial mechanical robustness, but it involves moving mass that is not conductive and doesn't contribute to ouput. I think about increasing the strength of conductive low resistivity density material sputtered or evaporated with a very light organic passivation to prevent degadation that is typical of such alloys. A different thing. Durability with more output.
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6th November 2009
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how about reynolds aluminum foils,

is this as good as the NOS rca stuff?
Les
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6th November 2009
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Quote:
how about reynolds aluminum foils,

is this as good as the NOS rca stuff?
You mean kitchen/household foil? It's ten to twenty times too thick.
Some DIY experimenters use artist's faux silver leaf, but arguably it's too thin.

You see, as ribbon mass/thickness goes down output goes up...up to a point. When the acoustic impedance approaches that of air this relationship breaks down.

Optimum might be in the 2 micron range...ten times thinner than light duty kitchen foil. It can be had from specialist suppliers.($$)

Or do like I did as a teen ...peel off the 8 or so micron stuff from Gum wrappers and hammer it sandwiched between tissue sheets!
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