Paper Cone Strengthening

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I have purchased a couple of PA FU15-4 subwoofers that have treated paper cones.
It has been rumored that there cones can fold and then rip apart if overloaded.
I am planning to run these subwoofers to there limits and am wondering what I may apply to the cones to strengthen them from tearing apart?

They are new and I have not used them yet. I have see another FU15-4 run to its limit and noticed that the cone is not running uniformly across the cone. It has a bit of a warble effect across the cone(thinking lack of stiffness).

If anyone has any idea how to help this problem without telling me to turn them down please lend a hand.

Also I have a PA15-4 for test purposes so don't be shy to give up your wacky solutions. Sound quality degration is not an issue.
 
:D áfraid there is not much u can do without altering the drivers paramaters drastically :xeye: 'thou on 2nd thoughts you could try reinforcing ribs on the back of the cone like tannoy used on some of their drivers of yore....... dunno if anyone else could chip in with more pos advice? GM? PLANET 10? good luck and cheers:angel:
 
Thanks for your reply,
I have also entertained the though of reinforcement ribs on the rear.
Although I'm not sure what I would use material wise to do this.
Parameter changes are not a huge concern either being these drivers are only going to play from 60hz to around 35hz.
 
To be honest, you would have to see a failed unit to find the weak points. Willy-nilly reinforcements will only reduce sensitivity....which is perhaps a protection in itself ;)

Most likely failure areas are coil and spider and the junction of coil and cone, not the cone itself.
 
the problems i find while driving woofers to their max is usually tinsel leads melting

but

you are intrested in strengthening the cone i have seen a few people use fiberglass resin all it takesi s a thin coat on the cone and if you feel like it do the back side but dont get it on the spider or surround (of course)
 
Hi

I have tried varnish and acrylic glue ( which is stiff ) on parer cones. Both seem to work.

I have not noticed any detrimental affects for base/low mid but I have not tried on a mid range unit.

On the base unit the units were noticably stiffer after treatment and I believed provided a tighter base sound in a sealed box unit in comparison with non treated ut otherwise identical units. I did not take any sound measurements.

Don
 
Hi,
the concentric ribs seen on many bass drivers is, I think, a second layer of corrugations glued over the top of a paper cone. However this may be stiffening to reduce response anomalies at the high end of the frequency range.

The Tannoy type ribs are to prevent bending of the cone and extend well short of the voice coil former. Maybe a longer version that goes right upto the spider could help.

I have seen pics of horn loaded drivers that have destroyed the cone by repeatedly folding it due to lack of strength to push all that closely coupled air up the horn.

You could also add reinforcement from VC former to cone and a little beyond to help in that area.
I would try to minimise the weight added near the periphery of the cone. The forces needed to overcone the inertia of that remote mass must be quite big and worth avoiding.
 
I bought my first Tannoys (15" Monitor Gold) in 1971.

The surround was paper and in fact it was simply the paper cone thinned out and sealed.

Over the years the sealer dried out and the free air resonance rose.

In the 1980's I had the cone coated with cone dope to stiffen it and the paper surround replaced with a foam surround. Bass response was immediately improved.

In the late 1990's I became intriged by the use of the ribs in the HPD generation and when someone showed me that in fact the ribs were nothing more than electrical paper, I realized that I could add ribs to my old Monitor Golds and see what would happen.

Rather than using traditional grey electrical paper (used to insulate high voltage components in electronic products), I discovered a synthetic electrical paper made by Dupont named Nomex. In their series was a particular thickness that gave the best ratio of stiffness to weight.

Using some autobody filler, I made a casting of the curved profile of a portion of the rear of my woofer cone and then sculpted this casting into a curved wedge shape. Using this final form as a template, I could then cut the Nomex paper to shape so that once folded along the center line, the curved edges of the Nomex paper would line up perfectly with the rear curved surface of the woofer cone. I then used epoxy cement to secure the 4 ribs in place. Because the ribs were so light in spite of their 4" length, the mass of the woofer cone was hardly changed, but the stiffness greatly increased.

Now the Tannoy Monitor Golds sound better than ever and after increasing the cabinet size to around 14 cubic feet, I have a system resonance around 20 hz, instead of the 46 hz that I had before I ever changed the surround from paper to foam. I hear bass notes that I never heard before.

It has taken me 35 years and 5 cabinets to bring out the full potential from these speakers. Even my 15" HPD center channel speaker does not sound as smooth as my re-invented Monitor Golds.
 
That looks like a strangely constructed driver. Looks like the is spider on the front side of the cone. Hence there isn't much of the cone that you could get to. I'd think you would have to reinforce the rear of the cone.

I think what you want is to add maximum strength with minimum mass, as otherwise you will lower the fs and decrease efficiency, offsetting the advantages of handling high power. I think the most efficient way of doing this would be with ribs - not concentric circles but curved radial ribs running a curved line from the centre of the cone to the edge of the surround.

You could adhere these ribs to the rear of the cone. They could be either paper, light cardboard, or balsa wood, ideally with a triangular cross section. You could then lay a single layer of fibreglass matting or even carbon fibre over and add fibreglass resin. The paper/balsa wood is a light form and is easy to get into shape, but the fibreglass is what has the strength. The easiest way is probably take strips of paper, fold to form a spine, and put cuts along the spine to accomodate the curve if necessary.

You could possibly put a layer of fibreglass/kevlar/carbon fibre over the resultant cone to make is stronger again and so that the exposed surface looks homogenous.

This is for car audio right? Is it for SPL competition or just you like to play it loud? As others have commented, I'd expect the cone to not be the weak point, and that many other things would fail first, things that you can't change. Just a thought - pro drivers could be good for this application if its a car. The emphasis is on efficiency and on high power handling. Cabin gain will make sure there is bass as well. A number of pro drivers with combined efficiency of 100 db or more could do serious damage in a car!
 
Hi,
Thanks for the wonderful posts. These subwoofers were purchased with SPL competition purposes in mine.

As far as quality is concerned, the cones, and tinsel leads are the failing factor with these drivers. Many competitors have given up on them because of these two problems. These two problems aside, the voice coils quality, and drivers ability to produce very high SPL is incredible. To me well worth the effort to try and fix the two minor issues. Price is also an issue as these drivers are far cheaper then a comparable SPL woofer.

These drivers have two spiders as this pic shows.
I'm not a big fan of the accordion surrounds but have no plans to change them at this point.
http://www.caraudio.com/gallery/2/2/3/3/0/TroyV219.jpg

As I think I have mentioned I have a spare trial woofer that I will be experimenting with before I go ahead with the actual woofers.

This driver has ribs on front of the cone running from the coil to the surround.
http://www.thediscountmall.com/images/items/98550-powmofo15.jpg

Being my drivers have the spiders on the front like they do I'm sure there is no weak spot from were it begins to the former.
So far I am thinking similar to the above pic but of balsa ribs from spider to surround is the answer.

:confused: Please keep your ideas coming.:confused:

As far as the tinsel lead problem a small dab of automotive goop shaped properly will more then guaranty they won't tear out.
 
Very interesting driver construction!

Ribs on the front won't help much IMO. There isn't much cone that you can get to and I don't think it's worth it. Look at the back of the cone in that pic you linked - you have access to the cone there and it could be worthwhile. In the example, about half the diameter cone is covered, but in your case it would only be about a third.
 
Take pictures from every angle and post them. One might be able to guess the failure points from them. One might guess that where the front spider attaches to the cone is a weak point. A bead of epoxy around that (or ~6 matchstick ribs crossing that joint behind the cone) might help.

Failing that, just put the spare one in a box and pound the heck out of it until it breaks. Reinforce what broke..... pound it again... ;)
 
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I vote for that!

But I think the cure is different as I think the paper/cone will brake off in "flakes" - maybe "soaking" cone area around spider with thin glue - or a mixture of all the suggested, but problem is that you cant approch backside of spider, except perhaps "soaking" membrane from the outside/backside ??
 
ttvonau said:
Do you have pics you can send me of your Tannoy's ?

I'm sorry, these have already been mounted in a cabinet that is very difficult to open up as the cabinet is actually part of a wall system.

But if you were looking at the rear of the woofer cone through one of the four large diameter holes in the frame, you would see the light grey colored pieces of Nomex paper that are about 5 inches long and folded at 90 degrees along the center line and where the curved edges of the Nomex paper meets the curved rear surface of the back of the cone, you would see a thin bead of epoxy glue that joins the paper Nomex to the cone.

The rib spans from the surround all the way up to the spider. As found in the factory made ribs, I placed a hole of about 1/16 inch in the center of each of the two faces of the folded Nomex paper. I believe the hole allows for the air pressure inside the cavity created by the folded Nomex paper and the outer cone surface to remain at the same atmospheric pressure while the cone is vibrating.
 
Hi,
could the pin hole in the rib be for a method of holding the rib in a jig while the glue sets?

With that front mounted spider, is it possible to glue a dust cover over it to effectively increase the cone area?

What would happen to the pressure behind the dust cover as the cone moves towards and away from the pole piece?
 
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