I have never made something like this before, so my methodology was a bit of a stab in the dark. Luckily, my stab seemed to hit the mark. I started with a kids plastic cheerleader megaphone that I bought from the dollar store. Basically just a plastic cone of approximately the right shape and size for the base of the horn. It would of course need panels added to it to give it that trumpet shape we all recognize. I decided to try corrugated cardboard for the panels, because it is light, cheap and easy to cut and glue. I suppose I could have used cardboard for the entire horn, but when I saw the plastic megaphone, I thought it looked like it was something I could use, so that's what I started with. As it turns out, it was a a good move. The size pieces of cardboard I had to work with, added to the length of the megaphone made for the perfect length for the horn that I wanted.
I had only the vaguest idea how to go about this, so I started by making a paper template. I envisioned six or eight panels coming out of the plastic cone. I measured the circumference of the larger end of the cone and found it to be about 40cm. That divided by eight very well, so I planned on eight panels. I took a standard 8.5x11 piece of scrap paper and folded it in half to get a center line. Then I measured a 5cm segment that would fit to the cone and centered it on the center line. Then I just extended lines out to the far corners, giving me a trapezoid. I had no idea what shape I really needed, I was just figuring on a lot of trial and error.
I folded the lines instead of cutting them, figuring the fold would give it a bit more strength and stability for my test. I made eight of these paper panels and taped them together and had a look at them. It was actually not that bad. And it fit on top of the cone just about perfectly. I could have actually gone with that, but I did think it needed a bit more shape.
I figured that if I angled the line inward a little, halfway along the length, that would add more curve to the horn, or at least another segment of flare. What I really needed was to bring it in a little on both sides with a gentle curve, but I had no idea how to get such a curve and make it consistent. I didn't have anything like a french curve template handy, so I thought I would start with just a straight angle and see how that went. I brought each side in by 1cm, halfway along the length.
I made seven more of these, and taped them together, completing my second paper test horn. I sat it on top of the cone and it fit and balanced perfectly. To get something so flimsy to balance so perfectly on my first try was kind of creepy. It's not taped to the cone in the pic, it's just sitting there, balanced perfectly on the edge.
The angle I had added to the paper panel was taking me in the right direction. The horn had a much more pleasing bell shape to it, though still somewhat angular. But I decided not to press my luck by trying to go for a better curve. Since I was going for a steampunk version of a phonograph, a somewhat stylize horn would be OK. This would do.
I moved to cutting the panels out of corrugated cardboard. First I cut out one of my paper panels and traced it onto a piece of chipboard to make a tracing template. I wanted to make sure all my panels were exactly the same. I was also careful to make sure that the ribbs in the cardboard were running the same direction for each panel.
After cutting out eight panels, I started taping the seams together with masking tape. In my first attempt, I scored the panels at the angle so they would bend nicely at that joint. That looked like crap. What I ended up doing was to bend the panels over the edge of the table, kind of like the way you curl a piece of ribbed ribbon with a pair of scissors. This gave the panels a nice gentle curve that looked exactly like I had envisioned. I wouldn't need a french curve after all. This was supposed to be just a test fit, but when it went together, it fit so nice, I just left them that way. The majority of the tape is along the seams on the underside (outer side) so you can't see it in the photos.
I had originally planned to make the horn in two halves that could be fitted together on site. This would make transport and storage much easier, but that's not really working out so far.
Once I had all the panels taped together for the test fit, I sat it on top of the cone to see how it looked. Voilà!
I played around a while with several different designs to try to find a good way I could marry the cone to the panels in a non permanent way that could be done and undone easily on site, but without much luck. I ended up just gluing them together and covering the joint over with some papier-mâché. Then I coated it all in Mod Podge for a sealer and then a base coat of flat black spray paint.
It's hard to get much of a sense of scale from the pictures. The wide end of each of the panels is 8.5" long, making the circumference of the large end of the horn about 68", which would make the wide end about 22" in diameter.
Steampunk Phonograph (pt. 1)
Steampunk Phonograph (pt. 3)
Steampunk Phonograph (pt. 4)
Phonograph Prop Redux