044 silver coating

[ratitifb]

Hi Folks

a 044 pair just got home and the silver coating on one dome is flaking .

Is there any sounding issue ?

Has anyone ever successfully refinished these ?

Any ideas? Thx

[rdgrimes]

Best idea is to replace it. Without the aluminum coating it's not really doing it's job.

[BMWCCA]

Best idea is to replace it. Without the aluminum coating it's not really doing it's job.

What I've heard is the "deposited aluminum" is really a sort of spray paint.

According the JBL, the dome of the 044 is made of a "lightweight phenoloc material, coated with aluminum by means of a vapor deposition process". I don't think you can hurt it by carefully cleaning it up and spraying it with a fine coat of silver or aluminum spray paint. What have you got to lose?

[Baron030]

Since, one of my hobbies is astronomy and I have even made my own telescope optics. I know that aluminum is far too reactive to be chemically deposited on to a surface. So, deposited aluminum is not really like any spray paint. Instead, a physical vapor deposition process is used where the object to be coated is placed in a chamber and a hard vacuum is pulled down. After all of the air is removed, a small aluminum strip is heated to a point where it will then vaporize. These aluminum vapors will then condense on any cooler object. In a way, most of you have already seen this vapor deposition effect, without really knowing it. One of the reasons why an incandescent light bulb fails is because tungsten from the filament is vapor deposited on the inside surface of the glass bulb, which is why the glass on very old clear bulb will look kind of dark and cloudy.

Here is a link to a video explaining the aluminum vapor deposition process as it refers to telescope optics.
http://www.youtube.com/watch?v=9K49pVEEDwA

Admittedly, applying an aluminum coating on a JBL 044 dome is a lot easier then any optical surface. But, in both cases I would think that these coatings are extremely thin. The coating on a telescope mirror is only 21 atoms thick. So, I would think that even a thin coat of spray paint will weigh a lot more then the original deposited aluminum.

If the driver sounds good, then I would leave it alone.

Baron030

[BMWCCA]

So, what exactly is the surface we're dealing with? Definitions of "phenolic" seem vague to a layman like myself.

Dictionary: phenol |ˈfēˌnôl; -ˌnäl|
noun Chemistry
a mildly acidic toxic white crystalline solid obtained from coal tar and used in chemical manufacture, and in dilute form (under the name carbolic) as a disinfectant. • Chem. formula: C 6 H 5 OH.
• any compound with a hydroxyl group linked directly to a benzene ring.

Wiki: The properties of phenolic materials make them very well suited to myriad industrial applications. Phenolics are the result of polymerization between resin and a base material that can be paper, glass or cotton. The base material used is dependent upon the intended application of the finished product. Paper phenolics are used in the manufacturing of electrical components such as punch-through boards and house hold Laminates.

My guess would be that the dome material is closer to plastic than to metal. You can airbrush a far lighter coating than you can with commercial rattle-can paint. Is the coating actual providing a damping effect on the 044, or is it just to make it look like metal? :dont-know

[Baron030]

Is the coating actually providing a damping effect on the 044, or is it just to make it look like metal?

That is a very good question. It is very possible to deposit a thick and relatively heavy coating of aluminum to the phenolic substrate, which could alter the acoustic properties of the dome. But, I could equally wager that it’s done just to make the dome look like metal.

So, if the driver sounds good, then don’t fix what is not broken. The aluminum coating must be just cosmetic. But, if the driver does not sound right then no amount of spray paint will fix that problem.

Baron030

[4313B]

The 033 had the black painted dome and was "softer" than the 066 with its "brittle" aluminum dome via vapor deposition.

The story goes that when the vapor deposition machine final broke at JBL they didn't bother to fix it and resorted to paint. I remember hearing that the silver and gold 044 and 044-1 domes were painted. To spray the paint on one would probably have to use a model paint sprayer and make sure the layer was quite thin. Perhaps hand painting them would work better.

Or just leave them bare phenolic as suggested above.

[BMWCCA]

I've got one of these somewhere, under $20 (plus an air can) and the appropriate paint:

http://www.amazon.com/250-Spray-Gun-.../dp/B0006MZPLG

[Mr. Widget]

Has anyone ever successfully refinished these ?

Define successfully.

A number of years ago I sprayed Mirra Chrome onto a forum member's 033 or 044... can't remember which. It looked a lot like yours... afterwards it looked better, but not perfect. Mirra Chrome is part of a paint system that deposits extremely fine aluminum powder onto a substrate and creates a look very much like chrome. I used it in my model making business to create chrome accents out of plastic parts... http://www.alsacorp.com/products/mir...irrachrome.htm

It kinda sorta worked... the aluminum powder is finer than the aluminum you'll find in any paint and is held in a very thin ethylene alcohol suspension... when it is sprayed the solvent quickly flashes off and you are left with a fine aluminum deposition... if you spray it on a highly polished surface it will look like chrome. If the surface has a fine matte texture it'll look like matte aluminum. Unfortunately the cloth texture of the JBL tweeter I coated was coarser than a fine matte texture and this texture continued to show through the aluminum film... that said, an aluminum dome even with that texture looked better than the dark areas that had been showing through.


Widget

[BMWCCA]

The dome in the original post looks more like something got stuck to it, rather than a coating failure? Do we know the history? Language issues sort of imply they are new to the owner. Screens missing might explain coming into contact with something. Just curious. Might try a careful cleaning first?

[Mr. Widget]

The dome in the original post looks more like something got stuck to it, rather than a coating failure?

The one I worked on looked the same way... that is the phenolic impregnated cloth showing through. The aluminum coating is simply worn away.

Might try a careful cleaning first?

...and remove all of the aluminum?


Widget

[ratitifb]

very interesting replys. Thanks to all

The dome in the original post looks more like something got stuck to it

actually a coating failure really

...and remove all of the aluminum?

The aluminum coating seems to be cosmetic mainly and i'm thinking not for damping effect (metal vs phenolic ...)

If the driver sounds good, then I would leave it alone.

[rdgrimes]

The aluminum is not just cosmetic, it's there for it's rigidity and radiating quality. 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. This dome was designed with aluminum in mind. I stand by my statement that it should be replaced. The best analogy I can think of is the poly coating on woofer cones. You can peel off all the white poly coating on the old woofers and say it's just cosmetic because they still work. But that doesn't make it so.

[BMWCCA]

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!"

[grumpy]

I stand by my statement that it should be replaced.

All well and good, but with what? Last I understood the kits were NLA.
Otherwise, I'd agree. In this case, what's to lose? Get another, better
example on Ebay if it gets damaged or sounds like crap afterward.

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