This Instructable tells you how to make your own air-horn from common house-hold scraps.
With a little practice, each air-horn takes under five minutes to make, so an evening's work can produce enough air-horns for even the largest family to enjoy around the Christmas table, or to dole out as party-favours so that the dear little ones can take some of the party fun home to the parents who didn't help arrange the party... ;-)
Step 1: Equipment and Materials
A 35mm film cannister or similar plastic pot.
(You'll probably have to buy the balloons and straws, but you can scrounge film cannisters from your local photo-developing store. I get 20 or 30 a time from our local "Boots".)
Step 2: Drilling.
If you pause and check the fit every few turns, you should reach a point where the straw can be pushed snugly in without being crushed or distorted.
Drill a second hole in the side of the cannister, roughly the size of the hole in the base. Scrape the edges smooth, as this is where your mouth will be going.
Step 3: The Diaphragm.
Take an ordinary toy balloon and look at it. You should see that it has a crease around it. Since the diaphragm works best when it is flat, cut the balloon in half along the crease.
Step 4: Optional step - a big hole in the lid.
To this end, cut a big hole in the middle of the lid.
That's it. End of step.