Sounding the horn

I liked this little horn - it looks like the ones they had on the very first cars. The horn is a tube that has a stationary wave inside it. Assuming that this works like a trumpet, it will act as a closed-end pipe which will have an anti-node at the blown end and a node at the open end. The pressure difference as the sound hits the room pressure will cause some reflection of the wave back down the tube. As the reflected wave crosses the incident wave, interference happens to create a stationary wave. The length of the tube is one quarter of a wavelength for a closed-end pipe so in this case the wavelength will be about 60cm. The frequency will be 550 Hz which is well within the human hearing range. The bell at the end of a trumpet is about accommodating different resonances but here it may well just be to make the sound directional.