You can hear sound through an open window from sources that are not in your line of sight because of diffraction.

Question

Quizplus · Accepted Answer

Diffraction is the bending of waves around obstacles or through openings, and it allows sound waves to spread out and reach areas that are not in the direct line of sight. Therefore, it is possible to hear sounds from sources that are not visible through an open window, thanks to diffraction.

You Can Hear Sound Through an Open Window from Sources