Fixing tear in HDA driver

[buddam]

Hi all

I have a rip/tear of c.2 inches in one of the Audax HDA (aerogel) drivers of an old pair of KLS9 speakers. Is there a way to fix HDA (aside from school glue and coffee filter paper, which I have seen on the web as a solution for paper cones)? This may work to a degree but the added stiffness of HDA suggests it might not last long.


These have been long stored for a friend but I thought I'd give them an outing, with some new resistors and caps in the x-o.


In any case, how would a tear affect the sound?

Thanks

Adrian

[Phil Y]

Hi Adrian,

I have not personally handled a HDA driver but I would suggest a glue that to some degree matches the characteristics of the cone material, ie paper for a paper driver. If the cone is stiff and hard, maybe something like a thin piece of fabric and alraldite? If the tear is neat it could be glued on the back of the cone.
Araldite might not be the right choice but I'm sure you can see what I'm getting at.

Phil.

[Greg.]

I would try an application of glue on both sides of the cone. The glue needs to retain a bit of viscosity as it dries so it forms a slightly raised scab like covering over the split. Allow to fully dry and then apply a little Plasticoat paint to improve strength and appearance. A glue like PVA would be worth trying. Plasticoat paint remains flexible when dry and will add a little strength dampening to the repaired cone area covered.

Let us know how you get on as I’m sure your experience will be of interest to others who may face such a problem. Regarding using the speaker with the cone damaged, it is possible the split could open up and it may ‘quack’ when playing. Avoid SPL’s and subsonic music that causes excessive cone excursion.

Good luck!

[snowman_al]

I would try a latex glue (e.g. Copydex) and a paper or thin plastic (cling film?) patch first. It will be light and flexible. Plus, if you mess up it will peel off easily and you can have another go.
Not sure epoxy will stick to it for long and it will alter the stiffness in the repair area. (Most cones do not remain the same shape across the frequency range.)

Question is what caused the rip, has it just fractured or has it had physical damage?
Alan

[buddam]

Dear all

thanks for the responses. I have found some 'School glue' which I think is PVA-based. I imagine copydex is similar, but will check.

The damage was done in my cellar - the cone was physically invaded by the corner of a brick wall!

Will keep you posted how I get on

Adrian

[Greg.]

Good one, Adrian. Please let us know how you get on. I’m particularly interested because I have recently had to replace the dust cap on one of my Audax midrange units in my KLS3’s because the ‘vacuumer’ slammed the handle/hose into the driver

A tear in a diaphragm cone is another issue and if you find a good repair option, we would all like to know about that.

[buddam]

A result, I think! I used PVA school glue (£1 from Sainsbury's) for 5 of 6 strips of coffee filter paper (3 on front of cone, 2 on back). But the comment about Copydex's rubber base made sense so I left one problem area un-covered till I got some Copydex. I couldn't find any, but came across 151 brand 'Fantastic Elastic' glue (£1 from Poundland). Both PVA and the elastic glue have cured nicely overnight. I'll post before and after pics, but may have to do so on separate posts.

I took a short video too showing that the spring/flex/bounce of the cone has returned, whether I press on the damaged patch or elsewhere.

I am tweaking the x-o as well so won't play the speaker for a few days. Will report on sound then.

[buddam]

Previous post was before repair. This one shows the fix. A few more layers of pencil lead shading should produce more or less the right colour and the soft sheen of the HDA. The 2nd photo highlights the elastic glue, which remains a little shiny and tacky (a dry tackiness, nothing to worry about) compared to the PVA. There's nothing to choose between them as far as bonding goes. Hopefully that won't change when I start using the speakers

[snowman_al]

Looks a good result.
Thing with the latex glue is you can seal the little holes you have left with a couple of brush strokes, letting it set between applications.
Did you colour the paper before or after the repair?
Alan

[buddam]

It was the unbleached brown white coffee filter paper and I went over it very gently with pencil after repair