Stiffening Paper woofer cones.

I found an old pair of paper 12" woofers that sound great, but the cone is bending a lot and distorting the sound quite a bit. I am on a budget and am wondering if there is any way to stiffen up the cones. Could a thin layer of epoxy be put on top? What about epoxing little strips of cardboard (like from a legal pad) to the cone? Any suggestions would be appreciated. Thanks.
 
Hello Kingfoota,
I have used standard white PVA woodworking glue to treat the 10" cones on a friends guitar amp combo.
I thinned the initial coats with water so that it could soak/absorb into the cone and applied several more coats over a few hours.
This gave a very stiff cone, and nicely dead (quiet).
This worked very nicely in the guitar amp, with clean sounds and just the right amount of bite.

Hope this helps,
Regards, Eric.
 
Speaker repair

Please, use a thin epoxy glue and coat the underside of the cone, do not glue too many things to the cone or it will become too heavy and loose it efficiency and it will drop the frequency response. Find a THIN epoxy from a hardware store and it will last a few more years, also check that the bottom suspension is not warped or damaged. Good luck!
 
i have used a 50/50 mix of white glue and water several times with good results and have also used "the wet look" from parts express wich seems to do ok also.
the wet look is " a new generation of high gloss polymers formulated especially for the the speaker industry" "provides a protective coat of armor for you paper cone speakers"

i have used this on some early advents and it seemed to work ok but the glue water mixture also seems to work just as well and cost alot less.


mike
 

dex-rex

Member
2002-02-07 10:06 pm
Perth
Kingfootga,
I tried PVA,linear polyurethane...but epoxy works best for me!Epoxy coating will give the best ratio of weight to stiffness,whithout doubt.You can even add some glass or carbon fibres for ultimate rigid cone.I`ll recommend applying thin epoxy coating on both cone sides resulting in stiff "sandwich"membrane.Downside is that you MUST protect epoxy exposed to UV,meaning sunlight, with protective coating(e.g.two component polyurethane varnish or paint).How deep epoxy will penetrate into paper depends on its consistensy(viscosity) and I`m using West system 105 resin and 205 hardener with very good results www.westsystem.com .PVA is very good if you want broadband spectrum quality,sounding similar to polypropylene cones,but for the same stiffness PVA treated cone is heavier.PVA is much easier to work with.
Best regards
 

Legis

Member
2009-12-23 6:18 pm
Up! Has anyone tried steel epoxy to stiffen a woofer's cone? It weight's ~20% more than a normal epoxy, but I think it it's harder since it's used in repairing for ex. motor's cylinder head. I think the metal particles are usually titanium dioxide so it should be non-magnetic (does not react with magnets).

Thoughts?
 
Up! Has anyone tried steel epoxy to stiffen a woofer's cone? It weight's ~20% more than a normal epoxy, but I think it it's harder since it's used in repairing for ex. motor's cylinder head. I think the metal particles are usually titanium dioxide so it should be non-magnetic (does not react with magnets).

Thoughts?
A metal part won't "soak up" epoxy, so the strength has to be in the epoxy blend alone.
A high strength to weight ratio is created when the glue material can soak in to the substrate material.

Too much weight will affect the speakers parameters.

Even if the "steel epoxy" was thinned, metal particles on paper does not seem like the right direction to go for a high strength to weight ratio.

Might be good for repairing fractured aluminum cones though...
 

Legis

Member
2009-12-23 6:18 pm
I have decided to make an experiment to stiffen a woofer's cone with 162g/m2 carbon fibre sheet and transparent laminating epoxy. I will apply them to the backside of the cone. I'm also thinking to apply thin layer of epoxy on the front side of the cone to give it nice high gloss, varnished-like looks. This would also add one layer to the sandwich, which might increase the internal damping of the cone even more.

The cone I'm intending to stiffen is BMS 18S430v2, that has a cone made of mixed carbon fibre, glass fibre and sellulose, and is quite rigid already (but I want more ).

By adding mass to the cone I seek also to lower the woofer's Fs to increase the woofer's linearity playing below-Fs frequencies. I simulated increased cone mass with blue tack, and it seemed to reduce THD <30Hz frequencies, due the fact that a woofer is not so linear below it's Fs than above Fs, and by reducing the Fs the linear zone increases. This will also transfer some of the sensitivity from upper bass to lower bass, which is not so bad since I use the woofer only below 100Hz. I have no real need for 100-200Hz bass sensitivity, so I might as well exchange some to more rigid cone, better sensitivity and somewhat lower THD in the lowest notes.

Has anybody tried carbon fibre with epoxy to stiffen a cone?
 
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DrDyna

Member
2007-05-17 11:34 am
i have used a 50/50 mix of white glue and water several times with good results and have also used "the wet look" from parts express wich seems to do ok also.
the wet look is " a new generation of high gloss polymers formulated especially for the the speaker industry" "provides a protective coat of armor for you paper cone speakers"

i have used this on some early advents and it seemed to work ok but the glue water mixture also seems to work just as well and cost alot less.


mike

Buddy of mine that owns an audio shop refers to that as MSS, Magic Shiny Sh--.
 

Rewind

Member
Paid Member
2009-01-18 7:42 pm
Oslo
Nobody mentioned that it might be a good idea to put pressure on the cone while the glue is drying. I bet that is how they make these plastic cones, a la Proac. Then you need a mold of the cone, and also a negative mold of the mold you just made. Sounds like a lot of work, but should be very stiff. Funny word, "stiff".
 
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Has anyone tried polyurethane on a paper speaker cone? I haven't, but I did apply two coats of polyurethane to 3 inch diameter paper tubing, 1/16 inch thick. This paper tubing is commonly used to send things in the mail.

The two coats of polyurethane to the tubing made it much more stiff and durable. Polyurethane is a type of plastic, so applying it is plasticizing the paper.

My impression is that one or two coats of polyurethane doesn't increase the weight much, while adding considerably to stiffness.

Polyurethane is commonly sold in paint departments and sold for finishing wooden items, primarily, I believe.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
I found an old pair of paper 12" woofers that sound great, but the cone is bending a lot and distorting the sound quite a bit. I am on a budget and am wondering if there is any way to stiffen up the cones. Could a thin layer of epoxy be put on top? What about epoxing little strips of cardboard (like from a legal pad) to the cone? Any suggestions would be appreciated. Thanks.

For paper you don't need anything more than pva. As far as your phrase: "sound great, but the cone is bending a lot and distorting the sound quite a bit." I would ask: "what makes you think so?" Take a picture of them so we can see what you are working with. What kind of system are they in? Before I had measuring gear I ruined a set of 4" fullrange speakers playing with PVA glue (yellow woodworking type)...