Question

Why can't we hear an echo in a small room?

Answer 1

To hear an echo, there should be at least a distance of 17 m between the source of sound and the body from which sound is reflected. In small rooms this is not the case as the distance between the object and the source of sound is less than 17 m, so echoes are not heard.

Answer 2

our brain persists any sound only for 0.1 second so the time gap between the original and echoed sound must be 0.1 second. for this the minimum distance between the source and the obstacle should be 17.2 m. but in a small room this much distance is not there between the sound and obstacle so we are not able to hear any echo there.

hope it helped you. ☺