Home Made Horn Project

[WickedMessenger]

I've been seeing a lot of "repurposed" antique speaker horns used for acoustic i-phone amplifier stations for sale and got to thinking about how to make a replica of one rather than ruin a good vintage horn. This is not an attempt to exactly copy an existing horn but more of a learning experience in how to make a two-piece reusable mold that can be used to hollow cast horns. I thought some of you might find this interesting as I progress because there might be some interest in restoration work for parts that are hard to come by. I'm going to see if I can fabricate a horn that passes for the real thing, at least to the casual observer.

The first step is to make a model with a finished exterior surface from which the master mold will be made. The pictures below show the armature being made and then made solid with what will eventually be a smooth, perfect skin surface. The process is:
1)Design the horn. This one is 10" in diameter at the outlet and 1" in diameter at the inlet
2)Draw the horn using french curves on book board.
3)Cut and Glue the pieces together.
4)Fill the spaces with glued-in styrofoam and sculpt the styrofoam to form a solid underlayment to the first layer of paper mache.
5)Cover the armature with about 5 layers of paper mache.

Armature

Armature with styrofoam

With base layer of paper mache

[Curt A]

Interesting process... keep posting pics.

[estott]

I like your idea, but you've given it an odd bulge at the bend - still, keep up the project.

[howardpgh]

That looks like one of those big EMG horns. The ones that sag after many years.

[WickedMessenger]

More progress on the horn. I added two layers of a gesso recipe, one white and one blue. The gesso is made from drywall joint compound, Elmer's glue, and a bit of acrylic paint. It dries as hard as a rock. Then I sanded it with two types of sanders I have. It would have taken forever to do it by hand. The high spots are white, the darkest blue parts are the lowest spots. I'll keep adding different colors of gesso until I have a smooth surface and then I can cast a mold.

[Mr Grumpy]

Nicely done so far. Please keep the posts coming!

[WickedMessenger]

I've been adding layers of gesso and sanding between coats to get the final shape. Each coat is a different color so I know how deep I'm going. In retrospect I wish I hadn't done the first coat in white because it's too close in color to the paper mache underlayment and I didn't want to sand into that. But in order of coating they are white, blue, red, and green. At this point only shallow divots are left to fill so I won't do a complete coat of the next color, which will be gray. Then it's on to the mold making. Oh, and since some of you have decided to critique the shape of the horn, I want to say that this is an experiment in horn making and I wanted to post the process here. I didn't set out to make a duplicate of an existing horn. You can make any shape that you find appealing or attempt to make an exact copy of an existing horn. I have looked through Ebay and there are many horns very similar in shape to this one so it's not that weird.

After sanding green coat 2

After sanding green coat

[Mr Grumpy]

Does the Gesso sand easily? I was thinking of doing this with auto body filler, but that can be difficult to sand. Can you share the ratios of the three ingredients?
When I was younger and worked in the auto body trade we would spray the filler with a light misting of
semi-gloss black paint so when sanding, the low spots would be identified as a slightly darker colour.7

It's looking great!

[WickedMessenger]

The gesso is 1 tablespoon drywall joint compound, 1 teaspoon Elmer's Glue, and a small bit of acrylic paint -- probably less than a quarter teaspoon. I gave up trying to dry sand it because it's about 10 times harder than drywall alone and it was going so slowly. What I found was that if I wipe a section down with a damp sponge (but not too wet) I can sand it with drywall mesh sandpaper that I cut into strips and it goes very quickly. Going back and forth with the strip kind of like polishing a shoe around the round sections has refined the shape and turned it very round and I think you can see from the pictures that it has come a long way since the first coat of gesso. The low spots are very apparent when doing it this way because they are darker in color. I think Bondo would be overkill and more expensive and totally unnecessary. After all, this phase is just the mold pattern.

[Mr Grumpy]

Thank you.

I'm looking forward to seeing the molding process.