Question

why cannot be hear and echo in a smal room

Answer 1

HERE IS YOUR ANSWER

Echo:-The phenomenon of reflection of sound from a surface is called echo.

we can't hear an echo in small room because in it the sound can't be reflected back.

And 
For an echo of a sound to be heard,the minimum distance between the source of sound and the walls of the room should be 17.2 m.Obviously,in a small room echoes cannot be heard.

HOPES THIS HELPS YOU........☺☺

Answer 2

Because echo require 17.2 meters distance from the object to sound producer