Bracing a cone

[pdorman]

Hi all. Excellent to discover this forum! I picked up a pair of Wharfedale Dovedale 3's for a pittance (about US$7). (anyone ever had a pair of these? I'd be interested in any opinions on their quality) They are in pretty poor condition cabinet wise, but they appear to be worth putting some work into.

They sound fine apart from two things. First off, one of the 12" driver cones has a concentric failure - a line of weakness which compromises the rigidity of the cone. There are no splits or holes, and the weakness seems to be utterly consistant around the cone.

I am thinking of bracing this weakness from behind, epoxying small slivers of wood, about the size of match sticks in an array around the cone. Each will be separated by about 3/4".

Am I ...... INSANE?!!?

Second question: there also seems to be a rattle in one of the 12" drivers also, which also on occasion drops out completely. Is this likely to be a coil problem? Is it really, really hard to rewind coils?

Am I ...... INSANE?!!?

Thankyou all for your eyeballs.

Paul Dorman.

 

[kelticwizard]

You very possibly could be insane but there is no evidence of it in your two suggestions.

As far as rewinding the coils, I have not heard of such a thing done. I think it would require special equipment, but I do not think it is has never been done in history either.

The first suggestion-bracing the cone-was brought up by the famous DIY audio writer David Weems in one of his books. He basically recommended it for cheaper speakers, since cones are pretty carefully designed, but it is not like the idea is outrageous.

If the alternative is throwing out the woofer, just how insane can it be?

I have heard of re-cone kits, but have never used them so I cannot give you much info there.

Good luck!

 

[Variac]

Just trying to help!

I know nothing about this, but that doesn't stop a lot of people on these forums!

One idea is that they sell an insulation foam in an aerosol can that comes out soft and then hardens up. This might fix the woofer cone on the outside if you put about a 3mm thick layer around the outside at the failure. I figure this stuff is pretty light, but stiff. Glue might work with or without t he sticks. I think
Scan Speak, one of the top driver makers, purposely cuts the cones of some drivers and glues them back together to cut down resonances. Of course the cuts aren't concentric, but radial, but what the heck -give it a try!

First try to flatten the failure area as much as possible, because possibly your problem of intermittent sound is because the voicecoil is misaligned due to the messed up cone and is rubbing or binding completely. The good news is that if this is the case,
fixing the cone might fix this too.

Finally, you should do the same thing to both cones, because you will change the weight of the one you repair, and that will make it act differenytly than the other. They will tend to reproduce lower notes better and be less efficient to grossly simplify.