Diffraction is a typical feature of sound waves when they meet an obstacle.
That means the sound is audible in areas which are cut off from the direct sound incidence, such as behind obstacles.
Information and ideas:
Diffraction of light can be proved when a parallel ray beam of monochrome light is directed at a narrow opening. A screen set up behind the opening gives us a diffraction figure (bright and dark stripes that lose intensity the further outwards they are). With sound, a direct reference to the students' everyday world is even easier: Why can you hear noise from a street in front of a building even when you are behind the building?
Further information about this graphic is provided as an information sheet on the media portal of the Siemens Stiftung.
Relevant for teaching:
Vibrations and waves