Well, in order to further some speaker development work I've decided that a pair of round mid horns somewhat like the Oris or the Edgar are in order. I'm building a mold that will allow me to make as many as I want out of variety of hardening liquids. The first set will be made out of concrete reinforced with steel mesh.

The mouth diameter is exactly a freespace half wavelength at 300 Hz. The blue styrofoam SM represents the actual space in the mold where the 'horn' will be when poured, so you are basically looking at the outside profile of the horn in this photo.

This horn will be suitable for a 3" to 4" diameter diaphragm driver.

Rob

What are you going to make your mold out of? The rubber used for bronze repros is pretty cool stuff and I don't think it would melt your styro. And since molten sculptors wax is poured into it it might be able to handle a wide range of materials. The flexability of it for removal is one of the things I find attractive about it and it won't scratch like plaster.

Thatch,

Making molds is not an area of experience for me (yet). I was actually going to make the mold out of fiberglass cloth and resin. This would give it a bit of flexibility to help coax it off the cured piece and the rigidity to keep it's form.

Any suggestions for a release agent that will not harm the paintability of the concrete after it is removed from my mold?
Vaseline, motor oil, PAM cooking spray, vegetable oil (hey!) paste wax...? I know I don't want to use anything with silicones, or PTFE in it.

Thanx,
Rob

I would go with the Vasoline. It is the thing used for plaster of paris especially when you make molds of people. I don't recall it sticking to the plaster but if it does to the concrete some Woolite ought to get it off after it is cured, then you could put it on the tesla to quick dry it.
Joking about the tesla of course, :D

How about KY jelly?? If it doen't work its always useful for other things.

Mike:smsex:

Thanx guys for the advice on release compounds. What do you think of paste wax liberally applied?

Rob

Rob...wish I had some suggestions for a release agent for ya...but I don't :( However...this is a cool project ya got going...can't wait to read or see more. :D

Rob,
I would cover your original form with laquer masking tape or somthing like that to make sure none of the resin touches your form. It would eat a hole through that styro real quick I would think. Vasoline over that might be a good idea too. Maybe a shrink wrap?

Thatch,

I have already successfully formed the back of the mold on top of the styro you saw using a layer of Saran Wrap to protect the styro from the fiberglassing polyster resin. It worked but made mucho wrinkles which I had to fill over later. The mold is nearly ready to try. I temporarily gave the polyester dust a rest to work on my amp development. I HATE sanding that stuff indoors without a stiff wind.

Rob