044 silver coating

[BMWCCA]

BMWCCA - Phenolic is the material the cloth (linen?) is embedded in... sort of like glass cloth in fiberglass.

So what's peeling off? Keeping with the fiberglass analogy, is the "aluminum" "deposited" over a smooth finished cloth, like over the resin "gel coat"? Is it the binder coming apart and taking the "aluminum" with it? Like maybe the dome got smashed and poked back out, thus cracking the "resin"? The "aluminum" other than the part one would expect to be smashed looks fine. That's partly why I asked the OP to give us some history of this 044.

Just curious, but I do have a spare that needs to be "sucked" out.

[grumpy]

yeah... the aluminum is flashed on over the phenolic/cloth layering.
(or painted on)
That the phenolic/cloth sandwich is so thin is why you see the cloth
texture coming through. With the Al coated domes, you can actually
see the texture a bit better (perhaps thinner and more conforming to
the surface).

If it was pushed in, it was irreparably damaged... not that it can't sort of
work in an Ebay "doesn't affect the sound at all" sort of way.

[Mr. Widget]

BMWCCA - Phenolic is the material the cloth (linen?) is embedded in... sort of
like glass cloth in fiberglass.

Yes, phenolic resin... is used here just like polyester or epoxy resin is used with woven glass for fiberglass boats.

Keeping with the fiberglass analogy, is the "aluminum" "deposited" over a smooth finished cloth, like over the resin "gel coat"?

Exactly.

So what's peeling off?

The aluminum is simply flaking off.


Widget

[rdgrimes]

So the term "phenolic" is vague enough that the base material could even be closer to cloth than plastic? I can see now, I'm gonna end up dissecting one of my spares just to get to the bottom of this. I know, "Take lots of pics!"

It looks and feels like a dacron fabric to me. I have several that are aluminum-less. They feel completely different without the aluminum, very soft.

[4313B]

All well and good, but with what? Last I understood the kits were NLA.

I don't agree with JBL about discontinuing these kits. There are alot of the systems still out there in the field and they still sound very nice.

[SMKSoundPro]

I don't agree with JBL about discontinuing these kits. There are alot of the systems still out there in the field and they still sound very nice.

BUT>>>

They are.

Why can't we spread on some goo glue kinda stuff, then grab some of the wife's coveted ALCOA aluminum wrap from the drawer she hides it in, then start to work over the dome, just like a resin coating on a boat hull. I think I saw this once on the Science channel - "How it's Made." Certainly it should work and sound fine?

I've got a DOA 044 phragm just waiting to come back to life in a "Myth Busters" kind of way!


NO WAIT!

That's a dumb idea.

Sorry.

scotty.

see post: http://www.audioheritage.org/vbullet...&highlight=044

[ratitifb]

The aluminum is simply flaking off.

again

The aluminum is not just cosmetic, it's there for it's rigidity and radiating quality.

i probably agree with that

At the time, there was no way to economically construct a dome of aluminum like we do with titanium today, this process was the compromise.

regarding such alu dome like D16R2420 or D8R075 dias (except surrounding shape) what was the problem ?

see post: http://www.audioheritage.org/vbullet...&highlight=044

i read that very interesting post before and it was the reason of my 2nd question "Has anyone ever successfully refinished these ? "

But it sound better to leave my 044 alone when the coated dome is partialy masked by the front metal grid ...

[Mr. Widget]

regarding such alu dome like D16R2420 or D8R075 dias (except surrounding shape) what was the problem ?

Economics...

JBL did build and aluminum domed direct radiator called the LE30 in the early '60s... it was just too damned expensive.


Widget

[4313B]

Economics...

...it was just too damned expensive.

Which is also why they are moving to magnesium diaphragms in their compression drivers instead of beryllium.

[timc]

Really?

How does magnesium compare to beryllium and titanium quality wise?


-Tim

[Mr. Widget]

How does magnesium compare to beryllium and titanium quality wise?

The ideal diaphragm is infinitely stiff and massless.

Beryllium is the closest to that ideal followed by Magnesium and Aluminum... Titanium is the least rigid for a given mass...

This is why JBL is now using a lot of AL diaphragms in their current high end home speakers. Years ago they stopped using Aluminum diaphragms in their pro compression drivers due to mechanical failure during prolonged high power use.


...and once again we have drifted a bit off topic.



Widget

[rdgrimes]

The ideal diaphragm is infinitely stiff and massless.

Which to me says that a 044 dome without it's intended layer of aluminum is broken and should be replaced.

[4313B]

...and once again we have drifted a bit off topic.

Thankfully so... one can only chat about an 044 dome for so long...

Thanks for the post with respect to the various diaphragms. Oh, and they are dusting the magnesium diaphragms for those who are horrified by such things. I suppose I should have waited until next Halloween for the fightening revelation but oh well... Boo!

Which to me says that a 044 dome without it's intended layer of aluminum is broken and should be replaced.

Like I said, without the aluminum it kinda sorta becomes a slightly more powerful 033... just do what JBL suggested when this came up the last three or four times and put a thin coat of nice aluminum paint on them. If you screw them up you'll know it right away.

[lgvenable]

BMWCCA
Phenolic polymer refers to a phenolic polymer oligimer, which is catalyzed and thermally cured. These are very durable and water/chemical resistant. The same type polymer s used on hard to hold food , beverages, beer and other rigid packaging cans product side, which is the side exposed to the food we eat. Hard to hold, as fats and fatty food are tough to hold since they attack most polymers and soften them. Pet food, people food etc. The same type just different formulation is used on the public side (outside of the can,); just with different packages in it to help the coating survive the can forming processes.

These are also known as BPA based epoxy coatings.....which some tree huggers are out to ban.
See:
http://en.wikipedia.org/wiki/Bisphenol_A

btw this is what I help coat at Alcoa onto aluminum everyday, while I work on new non-epoxy based coatings to replace these. Trouble is lots of NGO's are against these emotionally (non governmental group); but rather than base an opinion on science we have had around for 50 years, they call it a "toxic chemical" and want to ban it. The FDA, European FDA, Japanese FDA all say "they;re safe".....but then again the NGO's have public opinion.....

OK OK end of a rant by a coating scientist.... Frankly BPA or BPA free...pays my salary either way; and keeps me off the streets at night......

If it sounds OK, why not leave it alone; either that or replace it, otherwise you're putzing around and might wreck the response. If it sounds right but aint pretty whats the difference?