I am getting my nerve up to open the LE85 compression drivers in my 42 year old JBL speakers and am looking for a suitable dampening pad to replace the ones that are in there now. It is kind of a chore that I have been dreading a little but think from what I have heard, that the open cell dampening pads break down and sometimes even turn to dust at some point. I ordered some open cell foam rubber but what came is quite heavy and dense and half inch thick (sort of like what a wet suit is made from) . I am pretty sure this wont be suitable but am wanting to get the right type of material on hand before I pull these very heavy drivers out. Has anyone did this replacement before? What density should I be looking for?
Suitable material for dampening pad on JBL compression driver.
Register to hide this ad
darkblue94
The Devil made me do it.
I'm just guessing but are you talking about damping material here? I really can't see any practical purpose for dampening one's compression drivers.
JBL calls them "dampener pads", and I am with you, wouldn't think the diaphragms would work well unless they were very light weight open cell type . The wrong weigh here might ruin the sound and possibly the diaphragm itself.I'm just guessing but are you talking about damping material here? I really can't see any practical purpose for dampening one's compression drivers.
I did read about someone using bubble wrap on a compression driver but that doesn't seem like a good option either. Not going to open those up until I have the right foam first.
BillWojo
Addicted Member
On Altecs the felt is not attached to the diaphragm, it's a good 1/2 inch away, stuffed into the rear cover. That diaphragm will put out a lot of energy from the backside of it as well, the felt helps absorb the energy and keep it from bouncing back and "ringing" the diaphragm.
BillWojo
BillWojo
That is good to know and makes more sense. I suspect the JBL may be the same now that I think about it. I have been chasing my tail on a certain sound or rather distortion that only reveals itself on certain music. Keyboard music seems to bring it out at a certain frequency only. I don't have any test equipment but have read that these pads disintegrate over the decades and can cause something similar to what I am hearing. From what I hear the foam isn't supposed to be stuck to the diaphragm either but to the cap, but as these pads break down pieces get stuck to the diaphragm which also can be bad on sq.
Maybe I am overthinking this, if the pad is never supposed to touch the diaphragm, but only to, as you said, absorb the sound that gets directed to the rear then it might not be as critical as to the material used. Certainly not as critical as having a rotting foam pad falling apart in there..
I think that I am going to do this next week when I have the house to myself. If the open cell I bought won't work I have some felt around that will do the job, I bought a bronze Philips screwdriver just for this job so that 10 pound magnet won't make me lose control. I have heard that a good thing to do also is to remove the diaphragm and blow out dust but then there is a risk of damage or not getting it back in alignment. These are probably impossible to get replacements for so may just inspect for cracks, clean old foam out and reinstall.
Just got through opening up one of the LE85's.. Wasn't bad but I found the whole thing stressful for some reason. As an electrician I have worked off and on my whole career where one slip of a screwdriver would be a disaster of one sort or another but I am retired now and just the fact that the diaphragm is so fragile and irreplaceable gave me a high degree of anxiety.. What I found was partially rotting foam, but largely intact. The foam was very light weight and porous in nature, and when touched turn to a gummy mess. This foam was glued to a piece of 1/8" felt in the back. So not having the JBL replacement foam I stripped everything out of the cap and cut new felt and then used sponge rubber, the kind that tilers use for grout. I have it all back together and the sound is quite good, can't tell any dramatic difference but will spend some time listening before I get the nerve up to do the other one..
