If a person is in front of a smooth surface from which a sound is reflected, the person would hear a sound that seems to come from behind the surface (B). In theory, the sound waves hit the smooth surface and bounce off the surface. The sound also repeats itself. This is known as an echo. There needs to be a time gap between the sound and the echo otherwise the listener will not hear the echo. It will still be present but form part of the original sound.
