Here is a long tube installed with one end closed. At the open end make a short, low noise.

What did you observe? 
You can hear a clear echo of your voice.

The science behind it :
For getting a clear echo, there must be a minimum time lag of 1/10th of a second between the original sound and its echo.The velocity of sound is 340m/s. The length of the tube is 18 meters. The sound wave travels 36 meters totally. The sound wave takes more than 1/10th of a second to cross the total length of the tube and return to our ears.