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I'm done sanding and adding gesso. The last layer was yellow and then I sprayed it with spar varnish to seal it against the molding process. I'll be making the mold next.

Too bad that's not the end product, I like the funky colors.

A very interesting and useful process!

What material will the mold be made of?

What material will get cast into the mold?

Thanks, Chuck

I've started to make the mold. Here we see the preparation by isolating half of the horn with clay and coating the horn and flange with the first coat of silicone. That will be followed by 3 more coats, the last 2 having polyester mesh embedded into the silicone. The final step on this side will be to cast a plaster "mother mold" over the silicone to give it a solid backing that won't distort in the molding process. I'll post pics of that tomorrow.

Chuck wrote:A very interesting and useful process!

What material will the mold be made of?

What material will get cast into the mold?

Thanks, Chuck

I'm still working on that. There are many options and I can do them all in the same mold so I thought I'd get busy with the mold while I research. One possibility is a "paper clay" recipe that uses paper pulp, drywall joint compound, elmers glue, and mineral oil. It comes out hard and can be painted and sanded to a luster. Since it is mostly paper fibers I think it will have the resonance of wood. But there are also hard plastic Part A / Part B resins that you rotationally cast into a thin coating until it sets up in about 2 minutes. You can add layers to make it as thick as you want.

The mother mold is done and setting up. Next step is to flip it over and do the other half of the horn.

The first half is molded and the clay has been removed. Next step: put mold release on the other half of the horn and the silicone flange and mold the other half and then add mother mold.

I just did a Google search for "home made speaker horn" and found this site. It's fascinating that I didn't see this before I launched into my experiment but he set about doing it the same way I did. He's making these horns from paper mache over a form that he made from plaster. If you go to this page and click on "View Slideshow" directly below the picture you'll see a lot more pics than just the single one on the page. I can't say I really like the shape but he's doing a good job making them. And for the price, they better be good. http://www.specimenproducts.com/buildin ... -speakers/ http://www.specimenproducts.com/buildin ... n-speakers

I'm probably jumping ahead but, are you planning on making a solid casting and then layering on top of that to make the finished product?

The mold is complete! Now to make some horns.

A note on the mold materials: I used Silicone I caulk thinned with naptha to make it paintable. It took 1 tube for each half. I used plaster of paris for the mother molds and reinforced them with burlap. The mold release was Johnson's Paste Wax melted to liquid and painted on. Total cost for these materials was about $45. I looked into buying mold materials online and it would have run into several hundred dollars if I had gone in that direction. I expect the horn materials will cost less than a dollar for each horn.