When you stand behind a sound source like speakers, you can still hear the sound because sound waves propagate in all directions away from the source. Sound waves are longitudinal waves, which means they travel by creating areas of compression and rarefaction in the medium through which they propagate.
When speakers produce sound, they emit sound waves in a spherical pattern, spreading out in all directions. This means that some of the sound waves travel towards the front, while others propagate towards the sides and even towards the back of the speakers. Even though you are positioned behind the speakers, some of the sound waves still reach your ears.
The sound waves that reach your ears from behind the speakers may be weaker in intensity compared to the sound waves that propagate directly towards you. However, sound waves can diffract and bend around obstacles, including the sides of the speakers, furniture, or walls in the room. This diffraction and bending allow some of the sound waves to reach your ears, albeit with reduced intensity.
Additionally, speakers are often designed to have a wide dispersion pattern, meaning they emit sound waves in a broader angle, which helps in distributing the sound more evenly across a room. This design feature further contributes to the audibility of sound even when standing behind the speakers.
Therefore, while the sound may be somewhat attenuated or altered, you can still hear it when standing behind the sound source due to the propagation characteristics of sound waves and their ability to diffract and bend around obstacles.