How to tell 2425h diaphragm is authentic.

[crtstudios76]

Greetings all. I got a jbl 2425h ceramic comp driver off of ebay for a song ( $75). The ad claimed the driver was working, and had a jbl diaphragm. Upon receiving my new toy, I inspected the driver to find the shippers had failed to destroy it! Bonus!!! Tonight, I fired it up, and it does seam to work well. It sounds clean, seems to cover the range I have dialed in ( 1k-8.5k). It does seem to be a hair quiet compared to my pair of similar drivers ( ducane alnico comps with 2425h diaphragms). Out of curiosity, I opened up the back to inspect further. I found a flat gray dome that does look like what I remember a 2425 titanium diaphragm looking like.
My question is how exactly can I tell it's a real jbl diaphragm, and not some cheap after market replacement? I can up-load some pics if necessary, but I'm betting one of the pros on here can clue me into the markings, or sticker codes that will set my mind at ease about this.

[yggdrasil]

If my memory serves me right the 2425H diaphragm should have a small green dot of lacquer on one of the terminals.

I can't guarantee that other manufacturers don't use this way of marking it, but haven't seen it.

[4343]

Green color on the "negative" (red wire) terminal is for 8 ohm, red for 16. The real tipoff is in the surround. Real JBL dias have a damping material on the outer half of the diamonds. It's a clear coating that shows up in the right angle of light. Have yet to see a copy that has it. A bright red "+" sticker is a sure sign that it's after market, although those fall off easily.:blink:

[edgewound]

Green color on the "positive" (red wire) terminal is for 8 ohm, red for 16. The real tipoff is in the surround. Real JBL dias have a damping material on the outer half of the diamonds. It's a clear coating that shows up in the right angle of light. Have yet to so a copy that has it. A bright red "+" sticker is a sure sign that it's after market, although those fall off easily.:blink:


So we don't continue the confusion on the vintage terminal terminology....

...the red wire inside the loading cap that attaches to colored diaphram terminal (green marking for "H"/8 ohm, red marking for "J"/16 ohm) which leads to the red spring loaded binding post on the driver is the "negative" terminal.

A photo always helps for ID purposes....but yes the D8R2425 does have a coat of glue around the outer half of the diamond pattern embossed compliance. There will also be some stamp printing on the underside of the mounting ring...usually something like a 5 digit code and maybe some other internal mfg codes.

The mounting ring that rests against the top plate has been a gold color anodized aluminum for about the last 15+ years.

Aftermarket diaphragm bottom rings are usually plain silver colored aluminum....of course, some might catch on to that;)

The thing that raises my eyebrow for your experience is the lack of output as compared to your other drivers of known origin. Aftermarkets are usually a higher DCR resulting in lower output.

Check the DC resistance of the voice coil for the D8R2425 is 3.2 ohms +/- 10%; DCR for D16R2425 is 6.5 ohms +/- 10%.

Hope that helps.

[crtstudios76]

As far as polarity goes..I think all of my drivers are backwards (jbl pro norm). I have 2235h's, the 2425h's, and 2407h's. Those are all positive terminal causes inward movement, correct?

Anyways..Ok.. I just cracked my Dukane drivers open. Those have absolutely for sure jbl titanium diaphragms. I did a comparison, and both the 2425, and the Dukane dias have a small green paint on the + terminal. They both have a diamond surround, and although the material is less evident, both have some coat of "stuff" on the very outside of the surround. The black plastic frame the diaphragm is built into looks pretty much identical down to the cast markings. As far as volume goes between the two, I have to admit it was a very informal comparison. I guess I can get some white noise going, and use a mic from the same position on both for volume to be sure. Alass, I do not own a working multi meter right now...

There is a small sticker on the outside of the 2425 diaphragm that has the markings of "35R JBF" Does this mean anything to anyone?

Anyways, with the two next to each other, I see little to no difference in these diaphragms. Unless one of the pros tells me the difference between a real one, and a fake diaphragm is too subtle for me to pick up on, given the details provided, I'll assume I got a square deal!

Thanks for all the input, and please do leave more info if you have some! Cheers!!!

[edgewound]

As far as polarity goes..I think all of my drivers are backwards (jbl pro norm). I have 2235h's, the 2425h's, and 2407h's. Those are all positive terminal causes inward movement, correct?


Yes for the 2235 and 2425, but the 2407 being newer is conventional standard + is positive....has spade terminals.



There is a small sticker on the outside of the 2425 diaphragm that has the markings of "35R JBF" Does this mean anything to anyone?



Yes...that's a current production date code sticker....I don't remember the code, but I should know it. I'll work on that.:o:


Thanks for all the input, and please do leave more info if you have some! Cheers!!!


Glad to help....seems you did get a good deal.:applaud:

[crtstudios76]

One more request for good advice!!! When removing, and installing one of these diaphragms, is there a way to safely do it, other than going slow, and careful?



Yes for the 2235 and 2425, but the 2407 being newer is conventional standard + is positive....has spade terminals.



Yes...that's a current production date code sticker....I don't remember the code, but I should know it. I'll work on that.:o:



Glad to help....seems you did get a good deal.:applaud:

[edgewound]

One more request for good advice!!! When removing, and installing one of these diaphragms, is there a way to safely do it, other than going slow, and careful?

Yeah...

The other way is fast and careless.

But...I like your way better:D