Question

Explain why can echoes not be heard in a small room.

Answer 1

A sound persists in our ear for 0.1s. At temperature ${22}^{\circ }C$ in air and speed of sound 344 $m.s^{-1}$, the total distance covered by sound between the point of generation and reflecting surface should be at least 344 m/s × 0.1s = 34.4 m.
Thus, the minimum distance between the point of generation and reflecting surface should be half of it i.e. 17.2m .
So, we cannot hear an echo in a small room as the minimum distance for the echo will not be satisfied. But we can hear an echo in a long gallery and big halls.