Foam in Back Covers of JBL Compression Drivers

[eso]

I just received a pair of 2425Js that I recently purchased. These were cheap with blown diaphrams. I'm converting them to H models (8 Ohm) for my Urei B series duplexes. This is the second pair of these that I've picked up and inspected.

Question is this: Has anyone noticed the foam in the back covers turning into a gummy mess over time? That stuff is nasty? What's up with that?

The foam will be replaced along with the diaphrams, but it's just weird that it gums up.

Has anyone experimented with other products in there? Years ago I ran some LMS sweeps on Altec 288 drivers with no foam, foam and 100% cotton quilt batting. There was no significant difference in any of the test curves.

What's the best replacement here?


eso

[SMKSoundPro]

Here you go:
http://www.audioheritage.org/vbulletin/showthread.php?t=26177&highlight=foam+pads

Scotty.

[robertbartsch]

This stuff is pretty nasty if not removed ASAP. I had a driver where the foam backing degraded and it left a sticky goo over every part inside the driver. I had to replace the diaphragm and clean all the parts.


Obviously, it is best to replace the bad foam with factory fresh foam but some have used felt from a craft store in a pinch.

[eso]

This stuff is pretty nasty if not removed ASAP. I had a driver where the foam backing degraded and it left a sticky goo over every part inside the driver. I had to replace the diaphragm and clean all the parts.

Denatured alcohol seems to work well for removing the decaying foam and goopy mess from the inside of the back cover and the leads (on both pairs I've opened up recently the leads from the binding post to the diaphram were embedded in the foam goop). The alcohol does not appear to attack any of the paint or the plastic ring for mounting the diaphram.

Has anyone tested other products it the back chambers?

eso

[toddalin]

Many of us have had good luck using using the rubberized carpet padding (that looks like multi-colored head cheese).

When I clean the old foam out of my drivers, I just scrape away the foam and leave the adhesive layer along the back (does no harm). I cut the padding to shape, give it a shot of spray adhesive, and press it in place.

[John]

Many of us have had good luck using using the rubberized carpet padding (that looks like multi-colored head cheese).

When I clean the old foam out of my drivers, I just scrape away the foam and leave the adhesive layer along the back (does no harm). I cut the padding to shape, give it a shot of spray adhesive, and press it in place.

Sounds like a perfect fix:applaud:

But I am not sure about the anal crowd that must have JBL issue replacment foam ;)

[eso]

Sounds like a perfect fix:applaud:

But I am not sure about the anal crowd that must have JBL issue replacment foam ;)

I'm a different extreme. I like natural things like 100% cotton batting or 100% wool industrial felt...


eso

[grumpy]

industrial felt...

If you do a search here, you should find a vendor and some part numbers,
depending on the thickness desired... even has adhesive on one side :)

http://audioheritage.org/vbulletin/showthread.php?t=26757&page=2&highlight=industrial+felt