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Ron K
11-06-2003, 01:22 PM
I want to know more about these. Does JBL make up their own. Is it available possibly in an aerosol or ? Do they coat one side only. I have 2 2425 I am maybe going to try treating this way if it could improve them. Any help greatly appreciated. Thanks, Ron

Earl K
11-06-2003, 03:09 PM
WOW ! You must really hate your 2425(s) if you're willing to sacrifice them to the paint brush.

Seriously though , to expect the same top end response as a stock 2425 when it is now carrying the added mass of a painted plastic coating, means some mass must of been left out in the first place. This is what JBL apparently does, their own literature states that they start with a dome ( diaphragm) weight that's about 20 - 25% lighter than usual. They then make up the difference with the painted plastic coating. This way they maintain HF extension and get a more damped diaphragm. Just the domes outerside is treated / painted .

Here are some ideas or alternatives for your science project.

(1) Buy some 275nd diaphragms from Giskard. These are the 1.75" plasticised titanium diaphragm you seek to create.

(2) Experiment with other components that add damping to the HF circuit. These are resistors and inductors and ferrofluid. It's amazing how much damping you'll get from just a 6 db Lpad with it's humble two resistors. Wire one up and listen to that first. Next, just for the heck of it, strap a 2.5mh coil across the terminals of the compression driver to find out what damping qualities it offers. A little bit of ferrofluid in the gap adds mechanical damping to the circuit. This also starts to reduce top-end performance.

(3) Still want to paint: Get an accurate digital readout scale. This is so you can find a way to accurately predict/track the removal of weight from the diaphragms' dome. This you would do by etching the dome with a carefully applied acid solution . Practise your etching chops on some other piece of titanium hardware. Acid solution strengths will need to be researched as well as the best type of acid to use.
Look for any plastisized paint/varathane that is water based and is advertised to adhere to all metal types. The previous etching should help adhesion.

(4) If you don't like the idea of doing this to your stock JBL diaphragms ( now getting pretty pricey ) then first try the whole process on a "Cannon" Sound ( AUS ) replacement sort. You may luck out and find they already start with a reduced mass ( remember the scale you bought ). I think these diaphragms are 1/2 to 1/3 the price - perfect - for the experimentally minded .

I'm out of ideas now <>Earl K

scott fitlin
11-06-2003, 06:24 PM
wouldnt it just be easier to just purchase and install the 275ND coated diaphragm?

:rolleyes:

Ron K
11-07-2003, 06:09 AM
Thats what I wanted to know. Didn't know they used a reduced mass diaphragm. I don't hate the 2425s that bad. It's the difference in them and the aluminum that gave me the idea. I tried ferrofluid years back on them and it degraded them, had to remove it. I will probably try that other diaphagm when I can afford it. Thanks for the help, Ron