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.
Step 5: Assembly.
Slide your straw into the bottom of the cannister until it presses against the diaphragm. Again, if you have a hole in the lid, you will be able to see where the end of the straw ends up.
That's it. The air-horn is made.
Go on, try it. Pucker up to the hole in the side and give it a blow.
Step 6: It Doesn't Work?
If all you get is a feeble hiss, keep blowing and gently nudge the straw harder against the balloon by tapping against the end of the straw.
On the other hand, if you just get silence and bulging cheeks you need to pull the straw out very slightly.
Step 7: Hacking the Make.
Yes, they probably will work. Film cannisters and balloons were just the easiest materials I had to hand, but I've also made one with a plastic snack pot and using the palm of a disposable rubber glove for the diaphragm.
Could you make one from a bucket? A dustbin?
What about the air supply? Blow too hard, for too long, you'll start seeing stars and have to have a nice sit down.
I made a basic model with a small inlet-hole, so it was a snug fit for the needle adaptor of a bicycle pump. That worked, honking nicely for every push of the pump. A larger stirrup-style pump I borrowed had a small air-reservoir, and with practice that gave a steady drone.
Tuning? What about tuning?
I haven't looked into this properly yet, but the note seems to be linked to the length of the tube you use, the tube's diameter and the tightness of the diaphragm.
Can you make it play a proper note? Could you make it tuneable?
Go on, enjoy yourself and don't annoy the neighbours too much ...