Help with Grille fabric loose on LSi-15

Jstas wrote: »

If other glues aren't sticking it's likely because there's still old glue there that needs to be scraped off.

Jstas wrote: »

K_M wrote: »

Jstas wrote: »

If other glues aren't sticking it's likely because there's still old glue there that needs to be scraped off.

well we used that Gorilla glue, a mess really, but got it to stick for a few months, but every part we glued, started to slowly unravel and pull loose again, in addition to parts that seemed to be held from the original glue.

We have older speakers *other brands* that never did this at all.
Maybe they used the same glue as the magnets on the old polk woofers...

I don't know what to tell you, then.

Don't know that the pot shots were needed here, they add no value. Also, don't really care about other speakers because the issue is with this one, not the others so why they factor into it for you is beyond me. If you thought so poorly of these speakers vs others, you wouldn't be making an effort to fix it, though, so not sure why you have to throw the sour grapes in with the dig at yet another speaker wholly unrelated to this.

Gorilla glue is some of the worst idea stuff I've seen. It works for it's original intended purpose but it's "do all" reputation/advertising is undeserved.

Most speaker grills that are made of plastic frames have the speaker grill material bonded on via heat bonding, aka: plastic welding. They aren't glued. So any glue on them is a previous repair. Most fabric is made of polyester and it's hard to bond it back on with heat by hand without melting through the polyester completely and ending up right where you are now with even less material to work with.

But if you want to glue fabric to the speaker grille, use an actual fabric glue. I've always had good success with 3M Trim Adhesive (or Super Trim Adhesive). It can be a bit of a pain to work with and not get everywhere but my experience has been best with a tube of the stuff and a tooth pick.

You will have to clean the area of all previous adhesives first. My suggestion is to use an emery board or emery cloth to sand it all away. Trying to scrape it off will just gouge the plastic underneath the glue. The emery cloth/board will leave a well prepped surface for bonding once you are finished removing all previous adhesives.

Jstas wrote: »

Yes, the melted plastic is typically smooth and shiny. Like super glue gets. It's the polyester that would be shiny as the base vacuum formed polymer would not have the components in the mix that would lend to a glossy finish, typically. Polyester is shiny by default which is why clothes made of polyester can look cheap and chintzy if the polyester isn't treated or the fabric isn't processed or blended with another material to mute the sheen. Most other plastics are dull in finish and need an additive to get the glossy finish in the final product.

All speaker manufacturers do the heat bonding the same with plastic grilles because it's cheaper. If the grille material is wood or metal they use adhesives or staples, typically. But modern speakers with polymer based grilles that are made using modern manufacturing techniques are heat bonded. It's a far more durable and permanent solution than adhesives. It's also significantly cheaper because there isn't a whole adhesive supply chain that has to be maintained, manufacturing processes are one step shorter too. That can be very significant because that step often means that there is no need for a machine and expensive tooling to apply adhesive. That reduces overhead in the manufacturing process significantly.

If there's any reason that the grille fabric is falling off it's because of the amount of contact area for the bonding. It probably could be larger to withstand the environmental factors that contribute to failure. I'm sure in testing that the grilles withstand a significant amount of abuse as is but sometimes testing doesn't take into account stuff like that spot the cat rubs constantly or the dog's tail whacks the grille repeatedly while it's waiting for you to give it a treat. Granted those are instances where it's fairly rare given all of the variables necessary to align to reach that point so you can't test or engineer for all of them or costs would be excessive and outside the targeted price point. So, I mean, stuff happens but it's typically assumed that if you're dropping 2-3 large on a pair of speakers you wouldn't allow abuse like that. Even so, typically it's not an issue but if the speakers are near a heat source like an HVAC vent or sit in a sunny spot or even near a high traffic area the material can fatigue and fail over time from the expansion and contraction of the heat cycling or from just the vibrations of people walking by. Add to that other variables like kid hands touching everything or pet bodies rubbing on everything or even tobacco or marijuana smoke and you start stacking failure opportunities on top of each other and when ganged up like that, it's not a matter of if but when it will fail.

To find an adhesive that will work with the grilles, look on the back for some formed or embossed symbols/letters/numbers and that should have the resin code in it or near it somewhere. Find the resin code, look at what the resin is made out of and then find an adhesive that will work with it.

Resin Codes:
https://en.wikipedia.org/wiki/Resin_identification_code

Also, stuff that is important is if it's a thermosetting polymer or a thermoplastic. All plastics will melt but not in the same way.

Thermosetting polymers are often liquid based and cured into a solid object and they won't soften with heat. They can be melted with chemicals though and when they harden again they are brittle and weak because the chemical that melted them dissolved one of the components of the resin and changed it to something different. You'll see stuff that needs to be rigid but light made out of these types of plastics. Stuff like power tool bodies or formed speaker parts or sporting equipment or kitchen utensils will be made from it.

https://en.wikipedia.org/wiki/Thermosetting_polymer

Thermoplastic will soften with heat and sometimes not a whole lot of heat either. Something like a black speaker grille cloth sitting in the summer sun can absorb enough heat to soften a thermoplastic enough to weaken it. Stuff like gas cans or pool toys or vinyl seats would be made from this type.

https://en.wikipedia.org/wiki/Thermoplastic


The reason some glues stick and some don't and some do and then fail quickly is oxidation. You need to find a glue that will work with your specific kind of resin otherwise it could fail. Some resins react with water and UV so something like Gorilla Glue would bond at first but as the oxidation increases, it's the oxidation that is stuck to the glue and it pulls away from the resin form. Others can dissolve components of the resin and break it down so it ends up failing at the basic molecular structure of the resin. Also, if you have a plastic that flexes, like a pool float and you use a rigid adhesive to fix it, it will fail at the adhesive point because of the lack of flexing. This is why you would use a rubber cement with a UV protector and a flexing agent in it to fix a vinyl pool float instead of super glue which is cyanoacrylate and basically cures into a rigid and brittle acrylic resin. Bonds like crazy and has a tremendous amount of tensile strength but very low shear strength so it can be easy to bust apart if you know how to get it to shear. (side note, Super Glue is non-reactive and sterile and if you go to the hospital to get stitches and they pull out the glue, it's hospital grade super glue. It's cyanoacrylate with a flexing agent in it. It's incredibly good at boding skin while creating an impermeable bio-shield to prevent wound infection)

Also, people laugh at me but aside from the 3M Trim Adhesive (used it for securing carpeting or upholstery fabric to custom speaker enclosures in cars to match interiors) for stuff that experiences significant vibration and flexing, this stuff works a treat:

https://www.parts-express.com/parts-express-speaker-repair-glue-1-oz-bottle--340-076?utm_source=google&utm_medium=cpc&utm_campaign=pla

I swear it's just Elmer's glue with a flexing agent but everything I've stuck together with it, even if it vibrates like crazy, is still stuck together. It likely wouldn't hold a speaker magnet on because the weight of the magnet and vibrations would cause it to exceed the shear strength of the glue but for gluing, like, a foam or cloth surround back to a paper woofer, it works great. I've also used it to repair older, foam based, speaker grilles that came unglued. It'll hold polyester acoustic fabric over the foam forms too. Dunno if it's worth a try or not.