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More on Doping Speakers

Posted 25th May 2013 at 10:25 AM by googlyone

I got a question or two on doping of speaker surrounds.

Here is the thing: If you buy an OEM cone kit it will either come with a pre-doped surround, or be provided with the doping material and instructions.

I have reconed a lot of drivers and until recently either used OEM kits or kits from providers who have looked after this for me.

A good example of a provider that gave doping compound was BEYMA. The instructions etc for this were idiot proof, and the material nicely packed in the kit.

To apply this I used a stiff "cleaning brush" as you would but from your local hardware store - a steel handle about 100mm (4") long crimped onto stiff bristles. Worked a treat.

The beyma doping material looked and smelt for the world like really thick PVA glue. The difference was that when dry it did not go that hard, and remained almost but not quite tacky.

The before shot is:
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The "after" use of the beyma clear compound is:
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Sorry about the speaker grille - I did not take any photos prior to completing this box and am feeling too damn lazy to unscrew stuff right now.

I also bought some doping compound from Queensland Speaker Repairs. The guy that runs this place is really nice, and is happy to talk over your problems.

I have bought several lots of things from him - the first was the recone kit for these less-than-common drivers. We talked over the possibility of getting an edge-wound voice coil, which in this case I could not (damn!). We also had some back-and-forth on the spider which in the first instance was not quite what I wanted.

He is happy to put together recone kits from parts to match damn near any speaker - and the prices were from my experience about what you would expect.

On the doping compound he has some opinions that perhaps it might be worth having a talk to him over. If you need this sort of stuff look up QSR on the net - you will find him.

Here is the thing though. The doping material I bought has a black coloring to it. I am not sure if this is simply dye, or some form of material he has added.

The close up picture:
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I only applied one layer, and the consequence of this is that it has not made the surround black - it has come out kind of patchy.

I think adding more wold tidy up the appearance but...
- The Fs pre doping was 34 Hz
- The doping immediately after the dope dried was 40 ish Hz. With no run in.
- After about 10 minutes of 10W at a low frequency the resonance had dropped 1-2 Hz. It clearly needs a solid run in to "loosen things up a bit".
- The driver once doped worked just fine, and behaved as expected in a box.

But will it ever get back to 34Hz Fs?

Will adding another layer increase the stiffness of the surround further?

Maybe I should call QSR myself....

The lesson to me in this is:
- OK so your cloth surrounds must be doped. No choice in this unless you simply want the driver to do stuff at high frequencies - and even then I would expect the surround to need doping to really work.
- The clear stuff is pretty benign in terms of appearance
- Colored doping material is the sort of thing that you ought to test on a "test driver" or a piece of test cloth before use.
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