An echo is a reflection of sound, arriving at the listener some time after the direct or original sound. The main conditions for hearing an echo are:-
1) There should be minimum distance of 17 m between the source of sound and the reflector.
2) There should be a time gap of 0.1 sec between the original sound and the sound received after reflection.
2 4 2
pls click thanks button above and mark as best since i answered first :-)
thank u very much