Here, two parabolic dishes are installed facing each other. Two people should stand infront of the dishes facing it and keep their mouth at the ring provided. One should speak in a feeble voice.

What did you observe? 
Other person can hear the voice clearly.

The science behind it :
The sound waves from one person, reflected at the first dish travels in a straight line to second dish and converges into a single point where we can hear the voice clearly. The property of reflection, convergence and divergence of sound can be seen here.