solvents for removing old foam

Kmevler

New Member
got cocky after re-foaming some old Cerwin-Vegas with kit from Simply Speakers. i had cleaned the cones of foam/glue residue with rubbing alcohol as per generally mentioned guidelines without any obvious problems. foam/glue off, alcohol evaporated, cone color and sheen uniform.

so... tried the same thing on a JBL J520M woofer. disaster! the edges of the nitrile polymer fibre cone warped and look to be destroyed. it looks like a drying up contact lens or like heat-warped plastic. technically the JBLs are more difficult to work with as these cones have the the foam attached to the back of the cone edge and therefore it is hard to simply scrape off. i was using Qtips with a genorous amount of alcohol and simply rubbing until Qtip no longer picking up any black residue.

was the isopropyl alcohol a mistake? probably. what else would anyone recommend? i may experiment on the damaged cone with some acetone. any thoughts appreciated.
 
Most pro's I've spoken to do not suggest using any type of solvent on the cones to dissolve or remove the old glues. You found out the reason why - it can literally take the cone apart in some cases. In other cases, there may not be any cosmetic damage but the fibers can swell and lose their cohesion, weakening the very part of the cone that needs to be strong - to attach the surround.

Also, I've seen cones get pliable or flexible in the outer circumference and then bend or shift under load or playing loud low frequencies, eventually leading to damage or failure of the cone.

Usually recommended to use a slight scraper type of implement, I've used a narrow wood chisel with good results. Important to take your time, try not to gouge out any big bits, and avoid taking all the way down to paper or cutting into the cone if possible. The old glue in some respects stiffens that area.

Call Simply Speakers or others and ask their opinion.

Acetone is an even more aggressive solvent so not sure you'll have positive results. Oh, one other thing, some cone-voice coil joints could soften when exposed even to solvent fumes so be cautious there and have plenty of ventilation. Certain plastic cone materials like Bextrene will melt when exposed to solvents. Polypropylene is usually pretty impervious but why take the chance?
 
mech986, thx for input. simply speakers did already reply: essentially - "(oh, well...)" without acknowledging that they in fact demonstrate the use of alcohol on their youtube tutorial. also, in a separate video they demonstrate gluing new foam to back edge of cone (big JBLs), but in their reply to me they say they don't recommend trying to attach to rear edge. this was never mentioned anywhere on their website. i guess i just got lucky with the Cerwin-Vega's. lessos learned...

email to SS "contact us":
"dear simply speakers, I had successfully refoamed a set of cerwin-vegas without any hitches using your kit and video tutorial and gained enough confidence to attempt a refoam of a pair of JBL J520M’s with your 5” kit. the main difference I could see is that the JBL’s foam attaches to the back of the cone, not the front. well, using rubbing alcohol like I did on the C-V’s seems to have warped the cone material and the demarcation between cone edge proper and foam residue is not at all clear. I suspect I got too aggressive with foam removal. regardless, I am now stuck with a cone that looks like a drying up contact lens (or a cornflake) – the outer edge is warped in waves now. the back of the unit is marked “MADE IN USA”, “MODEL P205G”, “P/N 76431”, “B5K-JBAE”. is it possible to replace just the cone without a “complete” re-coning (i.e.: spider, voice coil, shims, soldering leads, etc..)? or is there even an appropriate kit for these 5”ers? or is it just as easy/good/cost-effective to simply replace this speaker? I don’t know if it would be considered a woofer or a midrange when contemplating complete replacement. they sounded really good even with their visible foam-rot gaps and I’d like to try to resuscitate them (picked them up real cheap off craig’s list). I have only worked on one of the speakers, the other awaits satisfactory resolution of this first one. any advice would be appreciated.

SS reply:
"We have seen this is in the past. Sorry you had trouble. That is what [sic] we recommend installing on TOP of the cone no matter where the old foam was mounted.
The JBL 520M woofer is not an item we sell, nor a generic option. There is not a cone assembly either.
You might try the parts website:
www.harmanaudio.com
Good luck with it!
Please give us a call or e-mail if you need more information.
We will be happy to help you.
Regards,
Sean Ryan and the crew at Simply Speakers"
 
I use my fingers to remove the bulk of the old glue, cone edge between thumb and first finger, rolling my fingers back and forth. This works really well with no cone damage do this gently. There will be some remaining glue which is ok. Get the cone surface as smooth as possible when removing the old glue.
 
I use my fingers to remove the bulk of the old glue, cone edge between thumb and first finger, rolling my fingers back and forth. This works really well with no cone damage do this gently. There will be some remaining glue which is ok. Get the cone surface as smooth as possible when removing the old glue.

Yep. Use the alcohol to get the residue off your fingers.
 
I have found using "Strip-Eze" from the hardware store to be most effective. Brush on let set for 5 minutes themtake a scaper to remove!
Just did a set of CV 12" 3 days ago- worked great!
DC
 
Well, I can't say that Simply Speakers is all wrong, for the vast majority of paper cone or poly cone woofers, Iso Alcohol, at 71%, might work without much damage. However, not all cones are made the same, or of the same material. I don't know what the nitrile polymer fiber cone can handle in terms of solvents or even glues, but obviously the alcohol was not a compatible choice.

I don't agree though with the "put the surround on the front no matter were it was mounted before" attitude or advice. That's the easy way out for both them and the user - sure, its easy, but is it correct? For generic use, for casual listening, maybe. But for critical work, and for JBL and many other more precision made products, put the surround back where it was OEM placed.

It is just a little harder to prep, and a little harder initially to glue, but do a few and you'll find it straightforward. Even Orange County Speaker did that at one time, but they will put the surrounds as in OEM if requested. I will say though that with this 5" woofer, there isn't a lot of accessible opening on the back frame to use implements to get the old glue off, and to easily glue the surround on. Most likely would have to scrape off stuff using some dental picks, and then dry fit the surround, then apply bead of glue to surround, flatten the bead, then gently and carefully stretch around and under the cone edge, then find a way to press them together. Not going to be easy, so you could see why they would rather go front mount.

I suspect you're going to have to go looking for a replacement. Rarely can you replace only the cone as its too labor intensive to separate the voice coil and spider, then accurately glue them back up properly without some type of alignment jig, then install it again into the frame/magnet assembly. A recone is much, much easier if available.

You just missed a pair of woofer that sold yesterday for $30 shipped (item #371147866996) so keep looking.
 
Mounting position, front vs rear...

...I don't agree though with the "put the surround on the front no matter were it was mounted before" attitude or advice. That's the easy way out for both them and the user - sure, its easy, but is it correct?...

I've solidly confirmed this is NOT a good practice. Just for an experiment I mounted behind (without gluing in place), for a front mount, and the surround "raised" the cone, i.e. pushed it forward. This puts the VC out too far as well and changes the xmax for the driver. The same is true for mounting to the front for a rear mount, only in that case the cone is pushed in (or back if you will), again maligning the VC. I've proven this with several woofers.

I've only run into, cleaning, issues when being too aggressive with the solution I'm working with. That is why I use cotton swabs and/or q-tips for clean up. I've stopped using my finger nails and now use, almost exclusively, a razor. If layed almost flat on the cone you can peel away the excess foam, leaving only a minor residue.

I've serviced JBL, KLH, Advent, KEF, Pioneer, Radio Shack, Bose and many other brands of drivers. I've done Paper, Kevlar, Poly and other materials as well.
 
appreciating all the replies

thank you all for the replies. google searching really doesn't yield any definitive answers on either solvents / foam-glue removal best techniques / differences in techniques based on cone material / new foam attachment position. seems more like caution, experience, and artistry are what's needed (none of which i currently possess - but mistakes make for good learning). working space on 5" rear-attached is indeed tight. as far as the isopropyl alcohol - i think it was ok for the C-Ws (old D-2s) but disaster for the JBLs. must be the difference in cone material.

i think i just got lucky w the cerwin-vega project. look great - sound great. false confidence. i picked up 2 more jbl woofers $24 shipped from ebay but ... they both need refoam. so now i have 3 refoam jobs (other original + 2 ebays) to try to produce 2 good results.
 
I use a slightly dull X-Acto knife to scrape surround and glue residue from every type of cone body...and never use any solvents to try to soften the glue. Many X-Acto knife handles are only slightly larger in diameter than a pencil which makes them easier to use to get into tight places...and I also agree with others in this thread - ALWAYS attach a new surround to the same surface as the original. Attaching a new surround to the front of a cone body that had the original surround attached to the back of the cone body changes the position of the voice coil within the magnetic gap and causes some undesirable spider sag.
 
Ahh, so you did get them, :thmbsp:

As for definitive answers, Orange County Speaker Repair is one of my go to companies and is an Authorized JBL Consumer and Pro repair center for 40 years. When I spoke to them about solvents, they were the ones who gave an emphatic "NO" to their use on the cone edges. They only use solvents where needed for repair work near the cone/voice coil/spider and spider glue down points but that's more for complete rebuilds or recones.

Here's their instructions for the refoam process, using a feel process for centering. I prefer the test tone centering myself, otherwise the process for prep is much the same.

http://www.speakerrepair.com/instructions.html
 
Some speakers do allow for dry scraping, and of course one cannot be in a hurry. Think about it, what you're planning on repairing is probably 20+ years old adhesive!

But sometimes a little help is necessary. Currently working on a set of OLA woofers, which have the surround mounted on the backside....:-( so after working on the metal flange it was time for the cone. I used a welders brush dipped in acetone, just a quick wetting of the edge, and the glue/foam came off using a 1/4" wood chisel I keep just for speaker work. These are not a poly cone, so no problems there. Let them sit overnite, and ready for the install.

The rear mounted surrounds require more wine than the front mount style :D
 
Pix of jbl j520m thus far

i will attempt to show in pix some of my current decision dilemmas:

it appears that the entire face of the cone has been "varnished" up to and slightly beyond the edge of the cone proper. this has left a gummy pliable rim of glue and foam residue on the edge that cannot easily be removed. this is what i used the alcohol on the first time and that resulted in the "melting" and warping of the cone. likewise, trying to peel or tug off this residual material results in the contiguos layer of "varnish" becoming separated from the underlying cone. trying to cut the excess with even a brand new sharp sharp sharp razor just doesn't do well. it just won't cut cleanly. it's like Stretch Armstrong! i'll probably just leave it in place.

placement of new foam still remains a question: clearly: replicating oem backside gluing would seem best, however, the replacement foam i have (from simply speakers specified for this particluar model) may actually be configured differently. the inner rim does appear to be angled thus matching the angled edge of the cone. however: the "crease" where the angled flange on the foam begins is exactly level with the gluing surface of the outer flange of the foam. no "offset" either forward or rearward. with the speaker sitting face up, the edge of the cone is exactly level with the surface of the basket flange to which the foam would be glued and the inner edge of the half-circle portion of the new foam ring seems to be the exact same diam as the edge of the cone. if this makes any sense - then it seems that if i attempt backside gluing then the new foam will exert an ever-so-slight forward pressure on the cone (or another way to look at it is to think the cone will be forcing the new foam slightly bacward into the basket). if i glue to the front of the cone (waaaay easier) it seems it will not exert any force on the resting position of the cone. so which might be more prudent? you think the oem placement was supposed to slightly displace the cone forward?

probably waaaaay overthinking this for a pair of cheap craigslist speakers
 

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note how clean i got the flange of the basket. and note the translucent nature of the "residue" after de-foaming. this is why i think it is all one clean factory application of "varnish" to the entire front surface of cone after the oem foam was already attached to the backside. but don't let looks deceive - it is stuck tight and springy to the edge of the cone and won't pull or rub off without damaging the edge of the cone proper. nor will it cut, unless maybe i get out some teeny tiny scissors.
 
I always clean with the alcohol and re-apply-rub until no more black shows up on the rag. Every set of foams I got from simply speakers reacted to the adhesive, its somewhat strong causing it to wrinkle and curl around. Once the surrounds are set down in place and padded down everything is fine. The first time it scared me a little I thought something was going horribly wrong.
 
I personally would stay away from solvents as well. Slow careful tedious scraping is the order of the day. I personally hate doing JBL drivers from the 70's and 80's because many of them use that rubber/polymer cement that degrades into yellow brown jelly and turns the foam into a grey goo as well, especially on the backside of the cone where it's hard to get to. But OTOH the Aquaplas is a fairly rigid cone material that can handle a fair amount of scraping without tearing or buckling. I use a disposable scapel for that job, but a thin handled Exacto knife will work as well.

The only time I use any solvent is with the metal rim of JBL baskets, where I carefully wipe GooGone onto the old yellow gum/foam residue. This allows easier removal with a putty knife. However if you go this route, don't let pieces of the GooGoned residue sit on the paper cone after scraping or it might stain your cone material.
 
IMHO solvents are strongly recommended because there is lingering residue left behind from the old surround material and adhesive. It breaks down into a tacky oily consistency and even though it may not be visible its there. The manufacturers recommend using alcohol too, and they are in the business. Why chance it? My first re-foam job didnt go quite so well after a couple days of regular use the adhesive started letting go and the foams began lifting because I failed to clean the baskets properly by skipping that step in my preparation. Theres nothing worse then doing them and having to redo them!! Ive done a couple dozen pairs by now and all except the one were a success.
 
front or back?

here are pix of the first cone ruined by alcohol to clean back-side foam/glue residue. note the separation of front face "film" from cone paper and the warping of the cone.

still dithering on front vs rear attachment of new surrounds - any more thoughts? especially regarding resting position of cone when no surround is attached.
 

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IMHO solvents are strongly recommended because there is lingering residue left behind from the old surround material and adhesive. It breaks down into a tacky oily consistency and even though it may not be visible its there. The manufacturers recommend using alcohol too, and they are in the business. Why chance it? My first re-foam job didnt go quite so well after a couple days of regular use the adhesive started letting go and the foams began lifting because I failed to clean the baskets properly by skipping that step in my preparation. Theres nothing worse then doing them and having to redo them!! Ive done a couple dozen pairs by now and all except the one were a success.

IME, you are correct in the comment of the old surround material - it is a polyurethane foam which does break down. But most of the time this is very easy to remove without using any solvents precisely because it is crumbling off. As above, slow repeated passes with fingers, scraping or lightly applied blades will take that all off, leaving the old glue.

ON the cones, the old glue usually doesn't pose a big problem as the glue line is quite thin, and if too difficult to take off, can be left on. This is for the vast majority of refoams. The glue sometimes comes off because it has separated, and if it comes off without much of the cone surface, it can be removed without solvents. new glue and surround usually stick quite well if sufficient but not excessive glue is used, AND proper clamping pressure, AND proper curing temperature and time is allowed for the glue to dry.

Same for the old surround and glue on the frame, but it is usually easier to remove this because of access. Repeated scraping normally is all that is needed to remove the surround remainder, while the glue takes a bit more. Some are very anal about getting to really clean flat frame surface but its is not always necessary. This is the only area where some solvents might/could be used.

You can see below that some cone materials may not be compatible with solvents, and for most of us, there is no "hidden area to try for compatibility".

here are pix of the first cone ruined by alcohol to clean back-side foam/glue residue. note the separation of front face "film" from cone paper and the warping of the cone.

still dithering on front vs rear attachment of new surrounds - any more thoughts? especially regarding resting position of cone when no surround is attached.

Obviously, this cone is / was not compatible with the alcohol - it is a nitrile cone with an apparent laminate / layer coating of a plastic (for damping/stiffening or weather proofing) and both appear to have reacted badly to the solvent exposure.

If it were me, I'd find a nice place to use these as magnetic paperweights (caution leaving any magnetic financial or ID cards nearby) or for experimental purposes, but they won't be usable in this condition for your speakers.

The good cone can still be refoamed properly if the cone is its normal cone shape without any waves. Any waves will misalign the voice coil when glued up and the misshapenned surround will not respond with linear motion when used.

Edit: keep forgetting the OP did buy good used replacement woofers. Have they arrived yet?

IMO, use a nice sharp pointed blade to cut, from the front, the old surround out at the precise outer edge of the cone. This will take a steady hand and a magnifier will help you to see the joint. Then clean off the cone edge back of any residual surround without using any solvent. Clean with a dry swiffer to remove any dust, then run your clean finger over the back cone edge to remove anything else. Clean frame similarly.

If you have the test tone in your source, hook that up to a small amplifier, and hook your amp speaker wires to the driver securely. Gently apply amp volume till you can hear and see the cone moving and there is no scraping. Do not run in this mode for long or very loudly as the cone edges are not supported.

If it were me, I'd dry fit the new surround on the back of the cone and the frame to check for proper fit. If a little tight, the surround sometimes can be slightly stretched in all outward directions gently, but that usually is not needed. Then I'd suggest taking your surround glue with a Q-tip and applying it sparingly all around the cone edge with just the barest of glue on the front part of the edge - this should seal the front/top coating to the cone to prevent it from lifting off as the coating is not extending to the surround now. Let this dry for about 2 hours - don't worry, the glue normally will dry clear or black depending on the glue.

Then I would apply glue to the cone back circumference in a width enough to cover the inner flange of the surround - spread thinly and evenly within 5 minutes. Do the same with the surround inner flange, upper surface - the top side to contact the cone - but with even less glue, really thin but even. Try not to get any glue on the surround roll but don't be concerned if a little is there. Then a few minutes for both glues to get tacky.

This is the hard part - stretch the surround under and around the cone edge (just like you did when you test fit the surround dry), line it all up visually around the cone edge, then turn the driver over and press the surround onto cone firmly. I know access and visibility is limited so you might have experimented with various small thin flat or curved implements to reach in there, like when you were cleaning the cone edge. You might find something like tools used to trim or push cuticles around (in the nail care area of drug store or Walmart/Target) helpful, or curved hemostats, or the like.

Even and firm contact is important to allow both surfaces' glue to bond without air gaps - remember, less is more here, excessive glue will ooze out too much (a little is normal) and should have a still workable and movable ability for at least 10-15 minutes before setting up and not being moveable (just in case alignment is slightly off). Now let this dry for at least 6-12 hours.

Now using the test tone here is what I do - gather some large clothes pins or medium size binder clips, enough to cover at least 4-8 spots around the frame edge. Turn on the tone at low but audible level. Then clamp one outer surround spot to the frame, then the exact opposite. The tone should be clearer (less flapping slap) - then clamp 90 degrees from that (12-6, 9-3 like clock) avoiding the mounting holes. Then go 45 deg. and do the same again. Once fully clamped and the test tone sweetly purring without rubbing noises, turn off the tone. Then remove 2-3 clamps in a quarter region (up to half circle if needed) and then lay down a thin but even layer of glue on the frame, then press the surround evenly onto the glue. Turn on the test tone lightly to ensure still clean output, then turn off, reclamp. Repeat in sections for remaining surround area. When done, your test tone should still be clean sounding and you are completely glued up. Let dry 24 hours.

Any clamp marks will be covered by the outer cosmetic gasket, assuming you saved that or it came with your kit. If there is no outer gasket, let dry for 1-2 hours then carefully remove the clamps. If you are really worried about the cosmetics without a gasket, use a suitable curved piece under the clamps instead to apply pressure. The binder clips will apply a lot of pressure.

Then glue the gasket onto the outer front edge of the surround if you have it. Let dry for at least 12 hours. You could do this at the 6-12 hour mark of the surround drying.

Hopefully, after 24 hours, you will be done, test tone still clean, and now you are ready to hook it back up. Hook the wires back up in the polarity they were (you had notes or a picture showing the wire color to which terminal, right?), and reinstall into cabinet. Be sure there is a good seal from frame to cabinet.

good luck!
 
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