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Cracked woofer cone, Any tips for repair ?

qguy

qguy

Super Member
I am thinking of buying a 6 inch or an 8 inch cone (7 is not available), cut a rectangular 1 inch section and epoxy it to the back of the cracked cone.

If this approach is correct, is epoxy the best glue, would contact cement be a better candidate ?

Cone is 7" carbon-fiber-impregnated paper-cone woofer

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Would the glue and coffee filter be stiff enough? I am thinking a patch made a speaker cone (1 inch x 2 inch) in the back would be stronger. Is there a disadvantage to this ?
 
I'm not an expert but I would do a couple of layers with the coffee filter. Soak it in a solution of glue and apply it over the crack. You'll be fine.

But if you have sacrificial woofer cone even better
 
qguy said:
Would the glue and coffee filter be stiff enough? I am thinking a patch made a speaker cone (1 inch x 2 inch) in the back would be stronger. Is there a disadvantage to this ?
Click to expand...

Too big of a patch will add mass to the cone. There is a thread here about painting cones and many think that the added mass of the paint on the cone will adversely effect the driver. If paint can change a driver, I would hate to think what epoxy and a big patch would do.

Regardless, the best patch will be the one that changes the cone the least. That means the smallest, lightest weight patch possible.
 
I've used black fingernail polish on IMG cones on much worse damage, it was a permanent repair that didn't affect SQ at all.

On one repair the crack ran from surround to dustcap, the repair is still in operation more than 15 yrs later. The other was a hole punched through about the size of a pencil, with the material still slightly attached the nail polish made a permanent repair also still in operation.

Haven't had to try this on polypropylene yet, I hear it's a bit of a bitch to get anything to stick but nail polish would still be my first try. It comes in a multiple of shades and colors, even clear so matching shouldn't be difficult if a cone isn't the normal black.
 
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RTally said:
Too big of a patch will add mass to the cone. There is a thread here about painting cones and many think that the added mass of the paint on the cone will adversely effect the driver. If paint can change a driver, I would hate to think what epoxy and a big patch would do.

Regardless, the best patch will be the one that changes the cone the least. That means the smallest, lightest weight patch possible.
Click to expand...

It would be an issue on a tweeter but much less so on a woofer, especially one that diameter.
 
qguy said:
If this approach is correct, is epoxy the best glue, would contact cement be a better candidate ?

Cone is 7" carbon-fiber-impregnated paper-cone woofer
Click to expand...

@qguy how did it crack? Was it from use? If so, a patch may break again or it may crack in another spot. The crack is in a tough place as it goes right under the surround and it needs to stay rigid there. That said, epoxy is a good choice and I would make the repair in two parts. First, get the cracks aligned and glued back together with epoxy. Once it has fully cured overnight cut a strip of canvas, denim, or other heavy weave cloth. Work epoxy into it until saturated and apply it over the crack from the backside. That will strengthen either side of the crack. Hopefully this is at least as strong as an undamaged part of the cone. Good luck, proceed slowly.
 
Driver is Usher 8945a. Same cone is used as the Scanspeak woofer mentioned earlier.
No idea how it cracked. It is a hairline cracked, took me hours to find out what was wrong, I only got lucky when I placed the flashlight behind the driver and manipulated the cone and the light shone through. The cracked section is not visible without the light and without me manipulating the cone. You would not know it was there.
 
I have done the watered-down-white-gue and tissue trick on an old Bozak woofer - worked perfectly.
 
Cone tear repairs are always a bugaboo of gigging musicians.
The adhesive must remain reasonably flexible but have adequate stiffness in concert with the paper to be used.
The paper to be used must remain pliable and tear resistant after being layered in adhesive.
I have found the paper used for the common lens wipes to be quite resistant to tearing.
The Shoe Goo product which is toluene and perhaps butyl rubber (?) is strong and quite flexible.
I have repaired numerous cones for musical instrument amplification applications ( jensen P12, Utah, Herald Eminence, Altec ) in this manner with excellent results.
Whether it may slightly change the sonic nuance of this particular driver would remain to be seen.

Regarding Shoe Goo, I got carried away with it's usefulness and re-doped some AR and KLH canvas surrounds with it. Bad idea, as it does become stiffer as time goes by.
Luckily, it does dissolve with gasoline.
 
That looks like a heavy duty subwoofer. Make a patch out of something sturdy, like another old cone, and glue it to the back. A little extra mass won't hurt anything here.
 
podbaydoors said:
Cone tear repairs are always a bugaboo of gigging musicians.
The adhesive must remain reasonably flexible but have adequate stiffness in concert with the paper to be used.
The paper to be used must remain pliable and tear resistant after being layered in adhesive.
I have found the paper used for the common lens wipes to be quite resistant to tearing.
The Shoe Goo product which is toluene and perhaps butyl rubber (?) is strong and quite flexible.
I have repaired numerous cones for musical instrument amplification applications ( jensen P12, Utah, Herald Eminence, Altec ) in this manner with excellent results.
Whether it may slightly change the sonic nuance of this particular driver would remain to be seen.

Regarding Shoe Goo, I got carried away with it's usefulness and re-doped some AR and KLH canvas surrounds with it. Bad idea, as it does become stiffer as time goes by.
Luckily, it does dissolve with gasoline.
Click to expand...

Those lens cleaning sheets are a great idea, I have some and they are quite strong and thin too. Probably less mass and better than a coffee filter
 
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