Acoustic lens will focus sound waves like an optical lens focuses light.
A balloon can be used as an acoustic lens. A standard party balloon will work with higher audible frequency sound waves. A larger (1m diameter) spherical shaped balloon makes a vey effective lens for concentrating sound waves. The principle is that the gas in the balloon has a greater acoustic refraction than the surrounding air because the air in the balloon is compressed. Try filling the balloon with different gases EG CO2, natural gas, etc.
A solid satelite dish can also be used - replace the LNB with a microphone.