Question

explain why echoes are undesirable in big halls.

Answer 1

There are a many reason about this but the most on is--suppose you are listening to some sorts of sound in hall, if echoes persists then you will hear reflected same sound again an again which is undesirable so to avoid the same sound again so that not to get disturbed echoes are undesirable....

Answer 2

I would agree with "Saurab dulal"... I would like to let you know that this phenomena of echo production is known as "reverberation"....That's the reason why you can see curtain's at the end of the hall which absorb these waves(sound waves are 3 dimensional, simply longitudinal).The sound waves move back and forth , therefore the curtain absorbs the effect and stops the movement......Moreover there are other methods such as acoustic roof's that prevent this phenomena. If you have more question's regarding this please ask..