Magnesium Magic

[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.

[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]

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

[Robh3606]

From the year of the flood and completely different horn set-up. Looks like the original 9800! Funny how it evolved as new drivers and horns became available.

Rob

[Earl K]

Barry,

Thanks for starting this very interesting thread ( it prodded me re-read the 476Mg ) cut-sheet.

Now that it's newly planted in my brain, I see that the diaphragm is made from a Magnesium alloy called AZ31B

I remember thinking to myself when the Mg diaphragm was released, " How Great it will be to see these get released into the general retail channels" . Alas, that didn't happen.

Historically, alloys using Mg ( for HF diaphragms ) have been around for some time now.

Here's a mid-70's Japanese product that used an exotic alloy ( including Mg ) for the diaphragm material.
I doubt we'll ever know exactly what their alloy was, but it looks quite interesting.






The use of this alloy enabled the design enginners to achieve extremely wide band response ( especially in the lowest octave ).

[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

[Robh3606]

Here's a mid-70's Japanese product that used an exotic alloy ( including Mg ) for the diaphragm material.
I doubt we'll ever know exactly what their alloy was, but it looks quite interesting.

Hello Earl

Reminds of the original tangential JBL's

Rob

[1audiohack]

Hi Earl;

Thank you and everyone else for chiming in. It's a great experience to learn from you all.

The driver and diaphragm in your picture look very nicely made. We used to alodine some of our aluminum products and it looked very much like that pic. Not saying it's not mag.

I read the sheet on the mag alloy and the process. I have never handled magnesium foil but would love to bend some around and see what it feels like.

HI Ken;

One of those Be diaphragms is what I handled at JBL. Literally light as a feather, it just floats to the ground when dropped.

Hi ivica;

When the costs of manufacturing, packaging, warehousing, distribution, customer service and warranty are factored in, 400% over cost of manufacture is a fairly standard minimum retail sales benchmark, at least in my industry.

All the best!
Barry.

[ivica]

Hi ivica;

When the costs of manufacturing, packaging, warehousing, distribution, customer service and warranty are factored in, 400% over cost of manufacture is a fairly standard minimum retail sales benchmark, at least in my industry.

All the best!
Barry.

Hi Barry,

May be a piece of cake is "included". Neglecting the production cost of the Be diaphragm, all the rest have the Asian supplier while selling 2445 diaphragms, which in the USA (from the local USA firms) would cost less then 50 $......
In the USA original JBL 2445 diaphragms are selling under 100$, so for Be (diamond suspension) has to be 200$.

regards
ivica

[baldrick]

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.

Measurement 2451BE vs 476BE from another member on a different horn:

[ivica]

Measurement 2451BE vs 476BE from another member on a different horn:

Hi baldrick,

I think that here it is applied huge amount of averaging or smoothing. I have not get any time such smooth data if higher resolution measurements have be done. From my experience with BeX ( Be-Trex) diaphragm is that the FR response over 10kHz is fare away to be so smooth as it is shown here. It has been smother then SL or AL diaphragm, but not as seen here.
May be the BeX used in my experiments were wrong type.....I can wonder only.
I have no opportunity to deal with 476Be driver or its JBL original Be diaphragm, but I am 'almost sure' that such diaphragm would behave better over 10kHz, then BeX as a kind of different suspension has been applied.

regards
ivica
H