Question

Why do echoes produced in an empty auditoriumsusually decrease when full of people ?

Answer 1

echoes are produced when sound gets enough space and surface to pass through and to reflects. An empty room provides enough space which isnt blocked by any and also enough surface area for them to reflects. But in a room full of people, the volume of room is occupied many others. This will hinder the free travel of sound waves and thus echoes wont get produced 

Answer 2

Answer:

Echo is heard when the sound gets reflected back. In an empty room, the sound is reflected by the walls so the echo is heard. But in a living room there are so many sound absorbers present like curtains, furniture etc. They absorb sound instead of reflecting them and thus reduces the possibility of echo in the room.