|MadSci Network: Physics|
The answer to your question is resonance cavities. What is a resonance cavity? A cavity or hollow space in a certain area always has specific dimensions. These dimensions will give rise to what is called standing waves. A standing wave is formed when a wave is reflected back from a surface in such a way that it reflects back onto it self. Thus the wave is amplified and a sound wave will become much louder. When a horn is blown in a tunnel it is always a possibility that the specific frequency of the horn might be the same as the resonance frequency of the tunnel cavity. This might amplify the horn’s sound, which possibly could have effects like breaking a driver’s attention and causing an accident. I am not certain to how much the sound can be amplified – but if it was a very load horn there is the possibility that damage to the ears can be done – This is not likely but always a possibility. The amplification depends on how much of the wave is reflected onto itself, the frequency of the wave and the density of the air in the tunnel,and the dimentions of the tunnelalso plays a role.
Try the links in the MadSci Library for more information on Physics.