Cracking foam surround patching help!

[head_unit]

Built some speakers a long time ago, and one of the foam surrounds has a few cracks maybe 1 cm long each.

I do NOT want to replace the entire surrounds. Fuggedaboudit.

What I want to do is coat something on the top of the surrounds that will keep them working. Like rubber cement or Elmer's or...I have no idea, that's why I'm asking you all!

Something easily found at a hardware store or something would be nice. I'm just visiting here for a few days, so ordering some special goop means waiting until some other trip. I did see "silicon" mentioned in another thread, but what does that mean? If I go to Home Depot there are a bunch of kinds of "silicon"-which are not very thin but rather thick and sticky. With the cracks I have I need something like the consistency of honey or so, that I can gently brush over the cracks thin layers at a time...

Extreme purity of response is not important for these speakers, just want to keep them working...

 

[dantheman]

Maybe a fabric or foam glue from the arts/crafts store? Fabric ones should stay flexible and even assist in damping resonance. Check out Aleen's stretchable/flexible.

Dan

 

[speakerdoctor]

You're fighting a loosing battle. What you see in the crack is the beginning of the end of your surrounds.
Instead of patching, which may hold up for a few months, look into refoaming them yourself (tons of info. here and at audiokarma.org) or having them refoamed professionally.

 

[sreten]

Hi,

Something like white rubber carpet adhesive, e.g. Copydex. Use small
amounts initially into the cracks, then use a large amount very quickly
spread over the surround, but due to the back air access the surrounds
will still crumble, at some point they will need replacing.

Its not worth putting it off, its best to simply replace the surrounds.

rgds, sreten.

 

[DaveG]

I am not a professional speaker repair person, but I did not want to hassle with finding and replacing the surrounds, and I wanted to hear my new speakers right away! The high end was OK, but the woofer surrounds were in pieces, but still holding the cone in alignment. It was an odd value 28 ohm woofer with rotten foam, so I figured it was going to take awhile to find and get a replacement, so I elected to try a repair first, and then start the search for a replacement. (that was 1 1/2 years ago)

3M makes a black contact cement adhesive for door trim. The black is nice since it blends in somewhat with the original colors. I was able to buy it at an industrial supply in a medium size tube. It was recommended somewhere, maybe a speaker vendor, as the best adhesive to glue rubber surrounds to polypropylene cone material. Search for Dynaudio surrounds. Someone, somewhere mentioned the door trim adhesive. Most just said the white glue was OK but it does not seem to adhere well to the poly cone material.

I diluted the contact cement with MEK, in small batches, maybe a teaspoon or so, and then with a small model brush, painted the mix onto the foam. Eventually, after a few applications, on both sides, the surround was basically now rubber. The first coat was diluted quite a bit, and it soaked in. When the first coat dried, there was a noticeable improvement in the strength of the foam. Towards the last coats I did not dilute as much - just enough to allow smooth brushing.

The foam in my case was so bad that the weight of the wet adhesive would cause additional breakthroughs. Several of the real bad spots I laminated on a single thickness of cheesecloth, to hold it together till the first layer of adhesive set. I suppose patches of very thin similar foam would also work, maybe better.

The end result does not look great, and it had to change the characteristics, but mine was down firing. It seems to sound fine. Someday it will be properly repaired or replaced.
If your foam is in better shape, a single application may be enough, and not add to much additional weight. It shouldn't hurt anything, and is cheap, and I can still remove the repaired surround if I find one that is a perfect fit, or piece one close in size together, so not much to loose except a 9.00 tube of adhesive, which you will need anyway if you have poly cones, and a bit of time. It actually was completed during one weekend, so went pretty quick.
good luck,
Dave

 

[head_unit]

Hmm, I'll look for the Copydex and the other.

Yes, I guess eventually the surround material will disintegrate totally, that is true. But I don't have time to research and replace the surrounds as I'm only here a few days. And for these old 6.5" woofers, I'd probably just replace the whole woofer...but that would be another research project...

 

[DaveG]

Here is the stuff.
It is actually Loctite 30540. I got the MEK at the local hardware store.
Judging by the condition of my "repair" after 1 1/2 years, I would say it is going to hold up for quite some time. The rotten foam is basically encapsulated by the rubber. You might also try regular contact cement like "Goo" from a hobbyshop, but some products may remain tacky. This stuff feels like rubber when dry.

Loctite® Black Contact Adhesive, distributed by R.S. Hughes - Industrial Distributor - Tapes, Adhesives, Abrasives, Safety, and Electronic Products
( I actually used this Loctite product)


Shop 3M: 3M Super Weatherstrip Adhesive, 08008, 5 oz tube, Black
(this is probably the same stuff by 3M, and I found it listed in auto parts shops)

 

[dantheman]

The dope painted on a lot of surrounds stays tacky. I believe there is good reason for it, but dust will stick.

Dan

 

[head_unit]

The dope painted on a lot of surrounds stays tacky. I believe there is good reason for it, but dust will stick.

Dan

Hey, maybe the dust can reinforce my surrounds

Yeah, basically I like the idea of replacing/encapsulating the surrounds. If I was EVER going to actually get around to replacing any surrounds, it would be on another set of speakers my brother has, where the surrounds actually have holes...

 

[speakerdoctor]

I offer a cautionary note here:

If you're going to go the coating route, do ALL of the woofers. If not, you risk voice coil damage (much more expensive repair) if another surround should completely tear around its periphery unbe-knownst to you. You see, both the spider and cone surround provide voice coil alignment. With half of the alignment no longer in effect there's a much higher likelyhood of voice coil damage.

 

[kcollins]

I ran into this problem a number of years ago. After much investigation, I ended up using modified acrylic latex caulk from the hardware store. If I recall correctly, it was DAP brand, though I’m not 100% certain which one I used. DAP ALEX PLUS Clear would seem a likely candidate.

The material I used was milky white as a liquid but dries essentially transparent on the surround. Add enough water to thin (not too thick, you want the solution to penetrate the foam), then paint the surround repeatedly with thin coats allowing sufficient tine to dry between applications. If accessible, do the back side of the surround also. The result is a tough, flexible film which impregnates the deteriorating foam. I used this method on several Infinity subwoofers which are still in daily use some eight years later.

Not having performed any before or after measurements, I can’t document any changes to the driver performance, but empirically speaking, the coating does not appear to have significantly altered the drivers parameters.

Keith

 

[DaveG]

I'm going to try the DAP product when I get a chance and see how the flexibility and strength is. The contact cement worked well but between it and the additional MEK solvent, I had to do it outside in nice weather. The DAP caulk would be a lot more friendly to work with.
More options for the next unknown repair. Thanks, Dave

 

[Filius]

DAP ALEX PLUS Clear would seem a likely candidate.

Keith:

I registered just so I could thank you for this awesome idea. I too had an Infinity sub with a foam surround that was torn and had come unglued about halfway around the driver. I bought some acrylic latex caulk (siliconized) and diluted it with water as you describe.

I cut up an old tie to get some thin silk to patch the torn parts of the surround. I brushed the caulk mixture onto the foam and let it dry. Then I brushed on another coat, and put a piece of silk on top of it, covering the tear. Then another coat on top of the silk.

After it dried I put another two coats on the patches, as well as all the way around the foam surround.

Once it dried I hooked it up, and it works perfectly! The process leaves a smooth, clear, very flexible and strong coating over the surface.

I was so pleased with the result that I also removed the speakers from an old, 1950s era record player that I have. They had paper cones that were deteriorating, and in fact I tore one of them while removing it because the paper had become so thin and flimsy. But I brushed them with the caulk mixture, and used little pieces of tissue to patch the holes. Now the record player sounds a LOT better, clearer and more detailed, and the paper cones are no longer flimsy.

Some people have recommended Puzzlecoat to serve the same purpose, but I think the caulk is probably more flexible when it dries.

Anyway, this has been an extremely helpful discovery. Thanks again!

 

[speakerdoctor]

Keith:

I registered just so I could thank you for this awesome idea. I too had an Infinity sub with a foam surround that was torn and had come unglued about halfway around the driver. I bought some acrylic latex caulk (siliconized) and diluted it with water as you describe.

I cut up an old tie to get some thin silk to patch the torn parts of the surround. I brushed the caulk mixture onto the foam and let it dry. Then I brushed on another coat, and put a piece of silk on top of it, covering the tear. Then another coat on top of the silk.

After it dried I put another two coats on the patches, as well as all the way around the foam surround.

Once it dried I hooked it up, and it works perfectly! The process leaves a smooth, clear, very flexible and strong coating over the surface.....

What are you going to do when the other half of the surround tears?
I presume you'll do the same thing and by then you will have stiffened up the overall compliance and put the woofer's operating characteristics out of spec.
Good luck!

 

[Filius]

What are you going to do when the other half of the surround tears?

I coated both halves with the caulk mixture, which makes the foam stronger. As KCollins noted, he has done this and they have lasted for years without any trouble. So I don't expect the other half to tear unless someone or something tears it.

As far as the specs, that's a fair criticism. I have no idea how far out of spec it becomes. If someone has a premium speaker where adherence to spec is very important to them, then you're right, they might want to think twice before doing this.

All I'm saying is, I bought this subwoofer cheap, with a messed up surround, not working, and now it works. I only recommend this for people who just want to get a speaker working again, without having to spend much dough. Or if you have older, low-fi speakers like on my old record player, and you just want to reinforce them before they start disintegrating from age.