Besides being able to hear the sound when you are outside the door as in the illustration above, this spreading out of sound waves has consequences when you are trying to soundproof a room. This aspect of diffraction also has many implications. You may perceive diffraction to have a dual nature, since the same phenomenon which causes waves to bend around obstacles causes them to spread out past small openings. There are other factors such as the higher air absorption of high frequencies involved, but diffraction plays a part in the experience. The thunder from a distant strike will be experienced as a low rumble since it is the long wavelengths which can bend around obstacles to get to you. The thunder from a close bolt of lightning will be experienced as a sharp crack, indicating the presence of a lot of high frequency sound.

Another common example of diffraction is the contrast in sound from a close lightning strike and a distant one.

The fact that diffraction is more pronounced with longer wavelengths implies that you can hear low frequencies around obstacles better than high frequencies, as illustrated by the example of a marching band on the street. Diffraction in such cases helps the sound to 'bend around' the obstacles. The fact that you can hear sounds around corners and around barriers involves both diffraction and reflection of sound. Important parts of our experience with sound involve diffraction. Diffraction of Sound Diffraction of Soundĭiffraction: the bending of waves around small* obstaclesand the spreading out of waves beyond small* openings.* small compared to the wavelength

Background info about soundwaves