2450 diaphram problem

[pos]

A friend of mine bought used 2450J and after inspection discovered that the little metal part on top of the diaphragms was broken:

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This seems to bring audible distortion on one of the diaphragms.
How would you fix this? Remove the unattached metal parts with tweezers, of maybe fix them with a drop of glue?...

[Maron Horonzakz]

That fracture is going to get worse,,,Its better to just replace the diaphram..

[pos]

what could have caused this?

[subwoof]

many JBL Ti dai's had a small circle of aluminum *glued* to the top center - use some alcohol and soften/remove it and the glue THEN see if the actual dia is cracked.

Back in the old days i remember seeing colored red dots stuck all over the aluminum dia's by SR engineers / techs to dampen them on the bench..

sub

[cooky1257]

It's just a little aluminium sticker/dot stuck on as far as I know.

[pos]

So it can be removed without altering the stiffness or other characteristics of the diaphragm? It must be there for a reason, no? :dont-know:

[subwoof]

first resolve the audible issue with the suspect diaphragm. Specifically look for small cracks where the Ti material is fastened to the mounting ring. I have seen many of these develop cracks when they were run hard by large SR companies. I bought a group of 8 from a well known ebay seller in atlanta and 7 had cracks..:(

one test that will expose the cracks is to use a low level generator and sweep from 500 down to 100 with the back cap off. placing a finger on the diaphram near any "funny sound" will expose it.

make sure the gap is clean and the dia is aligned first.

[pos]

thanks!

[herki the cat]

many JBL Ti dai's had a small circle of aluminum *glued* to the top center - use some alcohol and soften/remove it and the glue THEN see if the actual dia is cracked.

Back in the old days i remember seeing colored red dots stuck all over the aluminum dia's by SR engineers / techs to dampen them on the bench..

sub

The aluminum dot is there for reinforcement in the stressed area of the folds molded on the diaphragm. Bending sheet metal at these folds results in work-hardening the metal leaving it vulnerable to early rupture.

BTW, In 1953, I restored __ a WECO 594-A, aluminum diaphragm to perfection __ that had a 1/4 inch diameter hole resulting from the previous owner leaving the 594-A in a puddle of water on his basement concrete floor.

I cleaned the corroded area with MEK and bridged the hole with a thin layer of cement from an Altec Lansing speaker diaphragm replacement kit.

We ran all the tests on this repaired 594-A in the RCA Camden laboratory and compared it to another perfect 594-A in original condition & found absolutely perfect performance at full rated power in this repair. :bouncy:

You can try this technique on the cracked 2450 diaphragm using epoxy cements to accommodate the the high power titanium performance.

cheers, herki

[pos]

My friend removed the remaining metal parts and got what looks like a clean and uncracked dome.
Should he put something there (a drop of glue, a small metal ring?...) to further reinforce the dome?

53544

[1audiohack]

In 1953, I restored __ a WECO 594-A, aluminum diaphragm to perfection __ that had a 1/4 inch diameter hole resulting from the previous owner leaving the 594-A in a puddle of water on his basement concrete floor.

I cleaned the corroded area with MEK and bridged the hole with a thin layer of cement from an Altec Lansing speaker diaphragm replacement kit.

We ran all the tests on this repaired 594-A in the RCA Camden laboratory and compared it to another perfect 594-A in original condition & found absolutely perfect performance at full rated power in this repair. :bouncy:
cheers, herki

Uuu huh,,,