An echo is not heard in a small room but it can be heard in hills near ravines.
why
Answers
Echoes aren't heard in rooms is that the reflected sounds are received in less than 0.1 seconds, or the reflecting surfaces are at distances of less than 17 meters. Reverberations can also be heard in an empty apartment.
Explanation:
An echo is a sound that returns to its source like a boomerang. In order to return back in the direction of its source, a sound or light wave must either trace a path in space that is reminiscent of a parabola (like the curvilinear motion of light traveling around the sun as a consequence of the curvature of space itself due to the sun’s gravity, as predicted by General Relativity) or simply, reflect from a surface. An echo is the latter, it is a reflection of sound waves from objects in the vicinity of the source.