Oops on first refoam effort on JBL J900MV

[jcqcomm]

Ok, I found this forum and the experienced DIY enthusiasts it hosts AFTER I messed up two of the four drivers of my newfound

I got 2 of these J900MVs with remarkably clean looking cabinets for a total of $14 at Goodwill. I knew the surrounds were trash. I thought the cabinets and XO parts would be worth that much, and maybe look for some drivers to drop into this. I have heard some great JBLs in the past, but I did not know, still don't know how good these might be. Posted opinions appear to be for middle of the road: Not great, but not trash either.

I discovered re-foaming was a quite manageable and cost effective option. Seeing the drivers to feel weighty and USA made, excitement levels steadily increased. I read instructions on simply speakers and other sites, and saw various videos. I proceeded to clean one of the 8" and one of the 6" drivers to an inch of their lives with careful scraping and, yes indeed.........., isopropyl alcohol on the back of the cones till most of the black goo had been removed Next day I discovered in shock that both drivers I cleaned looked like the pic attached. Others appear to have made the same mistake, but I found the available warnings only after it was too late.

My question to those who know JBL is two fold:
1. Is it at all possible to restore these cones to be flat and still round once again with a heat gun or solvents?

I have not found equivalent drivers on Ebay, but close ones (they have the 206 and 208 designation but different letters and different part numbers). Without the specs to compare I would not blindly swap the driver. I noticed the mid-woofer is in its own vented compartment so the complete assembly must carry some specific tuning.

2. Are there any suggested drivers that could be swapped in that are "close" to the ruined P206HS and P208HS units?

I had planned to clean the drivers first to observe the process experience before I ordered the surrounds, so now I am in an odd halfway predicament.

Happy New Year to all, and thank you for any shared suggestions for possibilities I could pursue.

John

 

[thomo57]

I'd say for $14 you've just had your first cheap lesson.
I may be wrong but I'd think you would be better off saving your cash on refoaming those.
Those cones look beyond redemption

 

[Brad Muller]

Like Woody The Woodpecker says.............

 

[Markoneswift]

I have refoamed JBLs before - those, I'm afraid, are trash IMHO. Looks like heat damage, sun exposure maybe.

 

[jcqcomm]

I have refoamed JBLs before - those, I'm afraid, are trash I MHO. Looks like heat damage, sun exposure maybe.

This was the state they ended up in after i cleaned the back edge with alcohol and Q-tips. Not right away, but after i left them
overnight

 

[ZOOM]

Never use alcohol on the cones.

 

[phansen39]

Seems your not the 1st one this has happened to.
http://audiokarma.org/forums/index.php?threads/solvents-for-removing-old-foam.637052/

Well they look trashed anyways so see if the damage can be undone. Re wet the back of the cone with rubbing alcohol. Set the speaker face down so that the edge of of the cone is in contact on all edges and nice and straight. Let it dry over night and see if the cone is now straight. Main worry would be is the cone gonna still be stiff.

Something like this:

 

[thomo57]

Seems your not the 1st one this has happened to.
http://audiokarma.org/forums/index.php?threads/solvents-for-removing-old-foam.637052/

Well they look trashed anyways so see if the damage can be undone. Re wet the back of the cone with rubbing alcohol. Set the speaker face down so that the edge of of the cone is in contact on all edges and nice and straight. Let it dry over night and see if the cone is now straight. Main worry would be is the cone gonna still be stiff.

Something like this:
View attachment 844782

Good advice as there is nothing to lose at this point.
Try what you can that costs very little and you may discover something that can be passed onto the AK community

 

[jcqcomm]

Good advice as there is nothing to lose at this point.
Try what you can that costs very little and you may discover something that can be passed onto the AK community

Thank you, phansen39. Indeed the post you reference was the one I discovered after the damage had been done.

I shall indeed experiment, with "nothing to lose". The inverted position is what I had in mind. On a ceramic tile for flatness, The edge of the basket keeps the cone just above the surface. I will look for some material from which I can make flat spacer disk(s) a few mm thick so the cone will rest on a flat surface under slight tension from the spider. I'll start with water and work my way up to other solvents. And yes, I will share any outcome, for better or for worse.

The drivers of the second unit have not been ruined, so I will have one properly refoamed unit as a reference for whatever the second one ends up as. Unless I come across the exact 6" and 8" units somewhere at reasonable cost, it looks like a AV room utilization will be out of the question, but these can still serve a dutiful second lifespan in my garage.

 

[bakes]

I refoamed a set of these for a friend. The cones had a bit of the warps that yours show, but not as bad (did not use alcohol on them). The foam smoothed them out immensely; the drivers are made of VERY thin pulp, and the coating seems to be the major structural part of the driver as far as stiffness goes. When you refoam them, use a really good glue; these things laugh at Aleene's and many other adhesives. Also, make sure you get a correct set of foams; generic 6" and 8" foams have too wide a roll.

 

[jcqcomm]

bakes, thank you for the encouraging reply.

Simply Speakers has a kit for both the 6 and 8" units that appears specific for this JBL unit (their part nr JBL-FSK-JBLMRV)

What what you deem to be a "really good" glue? Is there something better than the task specific glue Simply Speakers includes with their foam kits?

Thanks, John

 

[Markoneswift]

You might want to check whether your surrounds need to glue to the back or front edge of the cone, if you decide to go ahead. Many JBL speakers go on the back edge.

 

[jcqcomm]

On both these drivers they were glued to the back edge. A bit tricky to get to as the "spokes" of the frame are quite broad. This is why the q-tip and alcohol were such a seductive shortcut as it reached half way under a spoke with ease, and from two sides, the entire area under a spoke was accessible with ease.

 

[elitopus]

i have used isopropyl alcohol (and much worse) on quite a few cones. I have never run into this problem. Probably just because these cones are so thin. The other thread mentioned some thin cone JBL's as well

The pic of that cone is crazy. I would have never thought...

 

[GordonW]

Yeah, I just scrape off as much of the old foam as possible on those thin cone JBLs (and the Infinity SM series woofers oftentimes have the same issues for the same reasons), leaving the original glue "film" on the cone, and trying NOT to get into the paper itself. The idea is to just make a relatively smooth surface (free from bumps) for the foam to attach. Trying to make them perfect on the rear, just doesn't seem to work out well- it almost always winds up warped, creased, torn or something.

Fortunately, with the foam on the backside of the cone, it doesn't have to look perfect back there- just to be aligned properly and attached securely...

Regards,
Gordon.

 

[Markoneswift]

On both these drivers they were glued to the back edge. A bit tricky to get to as the "spokes" of the frame are quite broad. This is why the q-tip and alcohol were such a seductive shortcut as it reached half way under a spoke with ease, and from two sides, the entire area under a spoke was accessible with ease.

I reckon I would have just gone with a gentle clean of the residual rotted foam (a dry clean, that is, no chemicals). You can glue new surrounds to the front side of the cone no problem - I've done it a few times and could not hear any difference at all. Plus it's a fair bit easier

 

[bakes]

I tried Aleens and it was really slow to dry and loathe to adhere for whatever reason. The Simply Speakers stuff worked after a while, but there was a lot of blow dryer action going on to get it to set up.

And always always always attach the foam to the cone on the same side as it was originally attached. It does matter at high excursions.

 

[Hendry]

Ok, I found this forum and the experienced DIY enthusiasts it hosts AFTER I messed up two of the four drivers of my newfound

I got 2 of these J900MVs with remarkably clean looking cabinets for a total of $14 at Goodwill. I knew the surrounds were trash. I thought the cabinets and XO parts would be worth that much, and maybe look for some drivers to drop into this. I have heard some great JBLs in the past, but I did not know, still don't know how good these might be. Posted opinions appear to be for middle of the road: Not great, but not trash either.

I discovered re-foaming was a quite manageable and cost effective option. Seeing the drivers to feel weighty and USA made, excitement levels steadily increased. I read instructions on simply speakers and other sites, and saw various videos. I proceeded to clean one of the 8" and one of the 6" drivers to an inch of their lives with careful scraping and, yes indeed.........., isopropyl alcohol on the back of the cones till most of the black goo had been removed Next day I discovered in shock that both drivers I cleaned looked like the pic attached. Others appear to have made the same mistake, but I found the available warnings only after it was too late.

My question to those who know JBL is two fold:
1. Is it at all possible to restore these cones to be flat and still round once again with a heat gun or solvents?

I have not found equivalent drivers on Ebay, but close ones (they have the 206 and 208 designation but different letters and different part numbers). Without the specs to compare I would not blindly swap the driver. I noticed the mid-woofer is in its own vented compartment so the complete assembly must carry some specific tuning.

2. Are there any suggested drivers that could be swapped in that are "close" to the ruined P206HS and P208HS units?

I had planned to clean the drivers first to observe the process experience before I ordered the surrounds, so now I am in an odd halfway predicament.

Happy New Year to all, and thank you for any shared suggestions for possibilities I could

 

[Hendry]

Ok, I found this forum and the experienced DIY enthusiasts it hosts AFTER I messed up two of the four drivers of my newfound

I got 2 of these J900MVs with remarkably clean looking cabinets for a total of $14 at Goodwill. I knew the surrounds were trash. I thought the cabinets and XO parts would be worth that much, and maybe look for some drivers to drop into this. I have heard some great JBLs in the past, but I did not know, still don't know how good these might be. Posted opinions appear to be for middle of the road: Not great, but not trash either.

I discovered re-foaming was a quite manageable and cost effective option. Seeing the drivers to feel weighty and USA made, excitement levels steadily increased. I read instructions on simply speakers and other sites, and saw various videos. I proceeded to clean one of the 8" and one of the 6" drivers to an inch of their lives with careful scraping and, yes indeed.........., isopropyl alcohol on the back of the cones till most of the black goo had been removed Next day I discovered in shock that both drivers I cleaned looked like the pic attached. Others appear to have made the same mistake, but I found the available warnings only after it was too late.

My question to those who know JBL is two fold:
1. Is it at all possible to restore these cones to be flat and still round once again with a heat gun or solvents?

I have not found equivalent drivers on Ebay, but close ones (they have the 206 and 208 designation but different letters and different part numbers). Without the specs to compare I would not blindly swap the driver. I noticed the mid-woofer is in its own vented compartment so the complete assembly must carry some specific tuning.

2. Are there any suggested drivers that could be swapped in that are "close" to the ruined P206HS and P208HS units?

I had planned to clean the drivers first to observe the process experience before I ordered the surrounds, so now I am in an odd halfway predicament.

Happy New Year to all, and thank you for any shared suggestions for possibilities I could pursue.

John

Just had the identical experience. Had these puppy's over 20yrs.spent hours re_foaming and driver seems too taught to reproduce sound. I don't know if it's a result from an excess of alcahol during cleaning or long term sun exposure. Why is it near impossible to find replacements? Even if the originals aren't available ,why not others with same wattage/ displacement.

 

[jcqcomm]

Just had the identical experience. Had these puppy's over 20yrs.spent hours re_foaming and driver seems too taught to reproduce sound. I don't know if it's a result from an excess of alcohol during cleaning or long term sun exposure. Why is it near impossible to find replacements? Even if the originals aren't available ,why not others with same wattage/ displacement.

I believe to have learned the hard way that the alcohol was the culprit. While it appears as an innocuous cleaner, compared to acetone or some other heavy duty solvents, it is aggressive enough to ruin the delicate fiber blend used in the cones. Patient dry scraping and cleaning would have been the answer, a virtue I lacked at the moment of my engagement.

I wanted to clean the edges to an inch of their lives, so the alcohol sounded like a good suggestion. Again, after the fact, I discovers a cone that is not surgically clean can hold on to the foam adhesive just fine.

I had to park my project due to other things really keeping me occupied these weeks, but I have not given up. I am thinking with summer around the corner (this is Houston, and already 80 degrees F yesterday), a 90F garage may make the material more pliable under whatever experiment I might thrust at it. And if anything comes close to succeeding, I'll update this thread.

I may look into re-coning. A lot more expensive, and complicated, but as you observed, replacement drivers are hard, if not impossible to find.

I ruined only two of the four woofers in my speaker pair, so if re-coning is anywhere near reasonable of a financial option, I may pursue it as I am just curious how these will sound. I realize they are not KEF or Wharfedale, but I am curious enough to give options a try.

Good luck with yours!

John