Continuing my quest for noise makers I made one of these air horns. A membrane is stretched over the back of the horn, air goes in through the mouthpiece and escapes from the outer ring to the inner hole, as it does so it vibrates the membrane which produces a loud sound. The benefit of this design is that you can add a cone to amplify the sound coming out. I was a little disappointed by the volume when I made this before EMF camp, but at EMF camp I discovered that if I stretch the membrane tighter (with my thumbs in the hole) the noise became rather deafening. It certainly made people jump in our tent and was probably heard halfway across the field. I definitely need to remake one of these with a tighter membrane.