Magnesium Magic

[1audiohack]

Hi All:

I am a material geek of sorts and just found something that might interest some of you as well.


When JBL introduced Mg diaphragm drivers, I was baffled about how they could use such an inherently brittle material in a bending application.

In the automotive racing world, we are familiar with magnesium and its properties. Formed parts are wrought at elevated temperatures of about 200 - 400° C. and virtually all other parts are castings.

Initially I assumed that JBL must use a surround of different material, something similar to what Materion has employed in the TruExtent diaphragms. I also assumed the domes must be formed while hot.

A couple of years ago on a visit to JBL Northridge I had the privilege to speak with J Morro for a while. My interest in materials led him to show me some unassembled diaphragms. I was surprised to see that the Be and Mg diaphragms had standard looking diamond surround forms like the 2445-2450.

He showed me a hard anodized aluminum diaphragm that was very stiff and light but he told me they fail at the surround as the anodizing makes them brittle. I mentioned that I was surprised that they did not mask that area where the bending would occur. I didn't prod as I was grateful for the time he spent with me and questioning him about it didn't seem appropriate.

Back to Mg:

I found an article on an relatively new process developed at Monash University in Melbourne Australia that makes it possible to shape pure magnesium at ambient temperature.

Professor of material science engineering Nick Birbilis states "The recipe is relatively simple: Pure magnesium is pushed through a die at 80°C, then cold rolled."

"This process changes the microstructure of the magnesium so that it is no longer brittle."

"By refining the microstructure, we have changed the deformation mechanism from intra granular (brittle) to inter granular (formable)."

Pretty cool! I wondered for a long time how they did it.

Oh by the way, "Duralumin" as used in JBL Al diaphragms is 2024 series aluminum, a very high strength aluminum alloy with good elongation properties whos major alloying metal is copper.

All the best!
Barry.

[ivica]

Hi All:

I am a material geek of sorts and just found something that might interest some of you as well.
When JBL introduced Mg diaphragm drivers, I was baffled about how they could use such an inherently brittle material in a bending application.
In the automotive racing world, we are familiar with magnesium and its properties. Formed parts are wrought at elevated temperatures of about 200 - 400° C. and virtually all other parts are castings.
Initially I assumed that JBL must use a surround of different material, something similar to what Materion has employed in the TruExtent diaphragms. I also assumed the domes must be formed while hot.
A couple of years ago on a visit to JBL Northridge I had the privilege to speak with J Morro for a while. My interest in materials led him to show me some unassembled diaphragms. I was surprised to see that the Be and Mg diaphragms had standard looking diamond surround forms like the 2445-2450.
He showed me a hard anodized aluminum diaphragm that was very stiff and light but he told me they fail at the surround as the anodizing makes them brittle. I mentioned that I was surprised that they did not mask that area where the bending would occur. I didn't prod as I was grateful for the time he spent with me and questioning him about it didn't seem appropriate.

Back to Mg:
I found an article on an relatively new process developed at Monash University in Melbourne Australia that makes it possible to shape pure magnesium at ambient temperature.
Professor of material science engineering Nick Birbilis states "The recipe is relatively simple: Pure magnesium is pushed through a die at 80°C, then cold rolled."
"This process changes the microstructure of the magnesium so that it is no longer brittle."
"By refining the microstructure, we have changed the deformation mechanism from intra granular (brittle) to inter granular (formable)." Pretty cool! I wondered for a long time how they did it.
Oh by the way, "Duralumin" as used in JBL Al diaphragms is 2024 series aluminum, a very high strength aluminum alloy with good elongation properties whos major alloying metal is copper. ....
Barry.

Hi Barry,

Thank You for the technical data information. Some more info about that would be interesting for me.
I believe that the whole technology dealing with either the AL (alloy), Be (alloy), Mg (alloy) is fare from being
easy, as very high tolerance product 3D shaped as diaphragm has to be made. NO to mention that JBL is
not producing 476Be diaphragms these days. Why ? Somebody said that at the beginning JBL has to pay about 100$
for each Be diaphragm to Materion, but such diaphragm had 'diamond shaped suspension'.
I think that 18-Sound have used Aluminum anodized diaphragms, but using 'plastic' suspension. I have no experience with
such type, but I have their ND2060A drivers, and over 12kHz they have not so good response (even they are 3-inch VC).

regards
ivica
H

[Lee in Montreal]

Hi Barry

Great reading. Thanks.

Lee

[1audiohack]

Hi Barry,

Thank You for the technical data information. Some more info about that would be interesting for me.
I believe that the whole technology dealing with either the AL (alloy), Be (alloy), Mg (alloy) is fare from being
easy, as very high tolerance product 3D shaped as diaphragm has to be made. NO to mention that JBL is
not producing 476Be diaphragms these days. Why ? Somebody said that at the beginning JBL has to pay about 100$
for each Be diaphragm to Materion, but such diaphragm had 'diamond shaped suspension'...

regards
ivica
H

Hi ivica;

I have not taken apart a 476Be yet so I don’t know for a fact that the production units have Be for the surround.

Be is very difficult to form. Foil is rolled from plate or ingot at elevated temperature in a can. The can is 308L stainless steel that is laser/electron beam welded around the Be in a vacuum. This can is heated and rolled to the desired thickness. The can is held between 650-900C or 1200-1650 degrees F and is reheated as necessary to maintain this temperature while rolling. Also it must be rolled alternately on 90 degree axis to maintain formability of the foil when later formed in a dome or other multi dimensional form. The can is anealed at about 500C or 950F and then sheared off of the Be. Further flattening and anealing is done between ceramic plates.

To obtain sufficient ductility and formability of the foil, BrushWelllman has to form the diapragms at 300C or 570F in a hermetically sealed heated forming chamber.

A little insight on why Be diphragms so damned expensive.

Barry

P.S. Thanks for this information goes in part to my brother who works in the nuclear medical world. Be foil is used among other things as windows on radiation source emitters and detectors.

[Mr. Widget]

I have not taken apart a 476Be yet so I don’t know for a fact that the production units have Be for the surround.

I’ve seen the JBL Be diaphragms at Materion where they are formed and they have a very similar geometry to the Ti diaphragms with a diamond pattern surround formed from the same rolled foil as the dome. Needless to say, they are quite proud of their ability to pull that feat off.

The voice coils and mounting rings are added to the diaphragms by JBL.


Widget

[pos]

Yet Materion uses polymer surrounds on their very own diaphragms, and are adamant that this is superior to metal surrounds in terms of LF response and metal fatigue.
Is that pure marketing and price cutting?

[Ian Mackenzie]

I have read recent forum member observations in other threads that the Materion Be diaphragm does not go as high as the 475 Be diaphragm.

This observation is consistent with why Jbl use the diamond surround to extend the HF response.


(They used the diamond surround with the 2421 and the 2425 diaphragm)

[1audiohack]

Yet Materion uses polymer surrounds on their very own diaphragms, and are adamant that this is superior to metal surrounds in terms of LF response and metal fatigue.
Is that pure marketing and price cutting?

Peter from Materion told me that the TruExtent diaphragms were designed to withstand the rigors of pro use. He said there was a redesign of the actual diaphragm early on that was more fatigue resistant.

The surround and the clearance between the phase plug and diaphragm will both affect the HF. I certainly understand that using a more compliant surround would be necessary to increased the LF performance while maintaining reliability.

Thanks Widget, I didn’t know for sure.

Barry.

[ivica]

Yet Materion uses polymer surrounds on their very own diaphragms, and are adamant that this is superior to metal surrounds in terms of LF response and metal fatigue.
Is that pure marketing and price cutting?

Hi Pos,

I think that the answer why JBL have applied metal suspension (diamond shaped) on all 4" diaphragm from the 2441 has been explained in their technical notes talking about first such suspension - such suspension would produce better UHF response then rolled or 'plastic' types.
I think that is why 476Be driver can reproduce almost 20kHz without diaphragm breakup (as Ti). LF response of such application is a possible problem, as 0.5mm amplitude (at LF) is may be too much for such suspension, so I believe that at Materion they have decided to use 'plastic role type' suspension, but such decision would give nothing special UHF response over 10kHz, and from MY point of view, UHF driver would become 'a must' for Hi-Fi application with BE (Trex) application.
It would be interesting to be seen comparative measurements of 476Be and 475 with Be(Trex) driver with the same horn applied.
I would expect almost the same differences as between 2440 and 2441 drivers.

regards
ivica

[edgewound]

Hi ivica;

I have not taken apart a 476Be yet so I don’t know for a fact that the production units have Be for the surround.

Be is very difficult to form. Foil is rolled from plate or ingot at elevated temperature in a can. The can is 308L stainless steel that is laser/electron beam welded around the Be in a vacuum. This can is heated and rolled to the desired thickness. The can is held between 650-900C or 1200-1650 degrees F and is reheated as necessary to maintain this temperature while rolling. Also it must be rolled alternately on 90 degree axis to maintain formability of the foil when later formed in a dome or other multi dimensional form. The can is anealed at about 500C or 950F and then sheared off of the Be. Further flattening and anealing is done between ceramic plates.

To obtain sufficient ductility and formability of the foil, BrushWelllman has to form the diapragms at 300C or 570F in a hermetically sealed heated forming chamber.

A little insight on why Be diphragms so damned expensive.

Barry

P.S. Thanks for this information goes in part to my brother who works in the nuclear medical world. Be foil is used among other things as windows on radiation source emitters and detectors.

If it's any indication of the construction techniques of the 476Be. The neo 2435 beryllium diaphragm is suspended with a kapton former. The voice coil is also encapsulated in a sheath of kapton to protect it from contact with the top plate/gap. The gap is very wide in relation to other compression drivers, probably due to the sheer force of the neo motor.

It'd be a pretty easy diagnosis to pull the loading cap off of a 476 to see the diaphragm construction. If memory serves, Greg Timbers told me ten years ago that the Be foil from Brush-Wellman is an alloy that is quite a bit softer than the TAD vacuum deposition process which is very brittle...it shatters in a million pieces if slammed into the phase plug. The Be alloy dome won't do that. It will dimple if pressed on...And yes, JBL at the time was paying $100 for each raw dome. JBL would then finish the assembly in-house. GT also told me the 045Be was not necessary as the 47Be was pretty flat out to 40Khz. He put his hand over the 045Be during the Everest II demo to show that it's real purpose was to satisfy the Asian market for a three way. There was no low pass filter on the 476Be top end. It just ran full open, with a hi-pass on the 045Be at 20Khz.

[edgewound]

If it's any indication of the construction techniques of the 476Be. The neo 2435 beryllium diaphragm is suspended with a kapton former. The voice coil is also encapsulated in a sheath of kapton to protect it from contact with the top plate/gap. The gap is very wide in relation to other compression drivers, probably due to the sheer force of the neo motor.

It'd be a pretty easy diagnosis to pull the loading cap off of a 476 to see the diaphragm construction. If memory serves, Greg Timbers told me ten years ago that the Be foil from Brush-Wellman is an alloy that is quite a bit softer than the TAD vacuum deposition process which is very brittle...it shatters in a million pieces if slammed into the phase plug. The Be alloy dome won't do that. It will dimple if pressed on...And yes, JBL at the time was paying $100 for each raw dome. JBL would then finish the assembly in-house. GT also told me the 045Be was not necessary as the 47Be was pretty flat out to 40Khz. He put his hand over the 045Be during the Everest II demo to show that it's real purpose was to satisfy the Asian market for a three way. There was no low pass filter on the 476Be top end. It just ran full open, with a hi-pass on the 045Be at 20Khz.

After a little investigation on the Materion website, there is a photo on the following link, right-hand side of page that shows what looks to be...Be...a 4" diaphragm that could very well be the JBL 476Be one piece with diamond pattern suspension.

https://materion.com/products/beryll...stic-beryllium

[Robh3606]

Part of the Mg magic is the rising response in the last octave in the large format driver 476Mg/Be. With the Be while doing the horn compensations you have to take the roll off in the last octave into account. The Mg diaphragms actually have a rising response which makes it easier to take the response out past 20K.

Rob

[ivica]

After a little investigation on the Materion website, there is a photo on the following link, right-hand side of page that shows what looks to be...Be...a 4" diaphragm that could very well be the JBL 476Be one piece with diamond pattern suspension.

https://materion.com/products/beryll...stic-beryllium

Hi edgewound,

I think that You are right. Interestingly Materion have shown us such picture, but they are selling 'plastic type suspension' 4" diaphragms. Why ?
If 100 $ have been enough for the Be dome with 'diamond metal suspension' , I can imagine that next 20~30 $ would be enough for the VC installed, so why they are selling their 4" Be dias with the 'plastic suspension' at the price about over 500$ per piece ???????


regrds
ivica

[RMC]

Hi Barry,

The battery of the future (electric cars, smart phones, etc.) may well be Magnesium based too. Just type "Toyota Magnesium battery" in your search engine to find all the info, example below.

Richard

P.S When I read it in the newspaper I remember the Engineer talked about 15-20 years before seeing it on the market...


"Toyota battery breakthrough means magnesium could eventually replace lithium."



"Toyota’s Advanced Magnesium Battery Breakthrough

June 22, 2016 by energypower


The key to using magnesium in next generation electric vehicle batteries has been discovered by scientists at the Toyota Research Institute of North America (TRINA).

The breakthrough came as Toyota principal scientist and chemical engineer Rana Mohtadi realised her hydrogen storage material might solve magnesium-based battery issues.

Researchers took magnesium borohydride and its derivative boron cluster compounds—a material used in hydrogen storage— and made it practical for magnesium battery chemistry.

Read the full article on www.bestmag.co.uk

Filed Under: Industry News"

[1audiohack]

Hi Guys;

I didn’t know how few of us would wonder/worry about Mg diaphragms. My 4365’s have them and while I don’t abuse them, my understanding (past tense) about Magnesium weighed on my mind whenever I played them very loud.

ivica, below is the link to the mind numbing (in depth) article (the kind I like and suspect you do to).

https://www.nature.com/articles/s41467-017-01330-9

All the best,
Barry.

P.S. An amazing demonstration of the process of ambient temperature metal extrusion can be found on the link here.

https://www.catalinacylinders.com/

Scroll down to the bottom of the page and view the video titled “Making a Scuba Cylinder”