When sound encounters an obstacle or a corner, it exhibits a phenomenon known as diffraction, which allows it to bend around corners and spread into the regions beyond the line of sight. While sound waves do generally propagate linearly, they can diffract or bend when they encounter an obstruction or an edge.
Diffraction occurs because sound waves interact with the edges of an obstacle or corner. When a sound wave encounters an obstacle or a narrow opening, such as a doorway or a corner, the wavefronts on either side of the obstacle bend around it. The amount of diffraction depends on the wavelength of the sound wave and the size of the obstacle or corner relative to that wavelength.
If the wavelength of the sound wave is large compared to the size of the obstacle or corner, diffraction will be significant. This means that low-frequency sounds, such as deep bass, tend to diffract more easily than high-frequency sounds.
As the sound wave bends around the corner or obstacle, it spreads out into the regions beyond, creating what is known as a diffracted wave. The diffracted wave wraps around the edges and continues to propagate, allowing us to hear sound even when the source is not directly visible.
It's important to note that the degree of diffraction depends on various factors, including the size and shape of the obstacle or corner, the wavelength of the sound wave, and the distance from the source. In some cases, such as when the obstacle is much larger than the wavelength, sound waves may reflect off the surface and not diffract significantly.
In summary, while sound waves generally move linearly, they can diffract or bend around obstacles and corners, allowing us to hear sound from sources that are not in direct line of sight.