One I found on this site by Robives
I like the simplicity and easy construction.
The design transfers quickly to thin metal.
Step 1: Gather Supplies
2 pine slats 1 in by 1/4 inch thick
poly wood glue
Solder iron or torch
sander and sand paper
Step 2: Make the Sound Chamber
Print and cut the shapes for the horn, sound chamber, and adapter
trace the shapes onto the brass sheets.
The brass is thin enough to cut with scissors but I used light shears.
Treat the brass like paper and fold it with a straight edge of light bending brake.
Clean the brass edges the apply flux and solder.
Step 3: Start With the Base
You will need to make the base from wood since the horn would be a lot heavier than paper.
I built the one shown quickly, without plans.
Prior to cutting the slats I glued 2 together on the edge to make a wide slat.
Measure the width needed from the sound chamber part of the horn.
Cut the cross piece so that the sound chamber is the max width.
Cut a second that is 1/2 inch narrower than the first
The side supports have the same front angle as the paper-craft but it is extended 3/4 of an inch back and then the back is angled down as shown.
The pieces are glued together and sanded on a belt sander.
Hand sanding makes a smooth finish then the whole base i stained to a desired colour.
Step 4: Meanwhile...
I used one paper piece to make a template from stainless for all duplicate pieces.
All fold lines are made by pulling the back side of an x-acto knife along the paper fold line.
I decided to change the design so that the securing tabs are on the outside of the horn instead of inside on the paper model.
Step 5: Solder the Shapes
I find that applying flux to the overlapping pieces then placing a small strip of solder to the joint.
The joint is then heated with a butane torch.
Continue until the model is complete.
Step 6: Oooh Shiny!
Be careful on the polishing wheel as the metal is rather light weight and will bend or rip easily
Step 7: Attach to Base and Enjoy
Clamp the glued pieces together as needed while the glue dries.
once dry, place the horn into the sound chamber. place the phone on the sound chamber and enjoy...