Question

what is echo prove that to hear a distance echo, the distance between observe and reflecting surface should be at least 17.2 m at temp ,say 2 when speed of sound is 344 m/s why do we hear echo in empty hall and not in well furnished rooms of same size

Answer 1

Echo is the phenomenon by which a sound produced is clearly heard back. There's is different term Reverberation which is caused by multiple reflection of sound and results in the simultaneous hearing of both the reflected and produced sound. This is because any sound we hear is retained in ear for a time period of 0.1 s, this is known as persistence of hearing. In reverberation the reflected sound is heard within this time period.

In the case of echo for the sound to be heard clearly it should reach us back after this time.

i.e $Distance=time*speed$

$time=0.1s, spead=344m/s$

$distance=34.4$

This is the distance traveled by the sound wave to the reflecting surface and back.

Therefore distance between the source and surface=34.4/2=17.2m

In an empty room, wall, ceiling, etc reflects sound wheres in a well furnished room he sound is absorbed by the polished surfaces.

Hope you're convinced. If not comment. Bye :-)