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]

Originally Posted by dantheman

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.