Question

why are echoes undesirable in big halls?

Answer 1

someone giving a speech would be interrupting someone giving a speech would be interrupting themselves interrupting themselves

Answer 2

echo means repetition of sound..If someone is speaking there will be two sounds..one which he is speaking right now and the other sound which he/she spoke earlier ..this will lead to confusion..in big halls the distance would be more than 17 m between the walls which will cause echo and not reverberation(prolongation of sound)