Parabolic mirrors that reflect sound
Late sources attribute Archimedes with the invention of burning mirrors, which he is said to have used to set fire to the Roman ships besieging Syracuse. A parabola-shaped mirror can concentrate the essentially parallel Sun's rays in a point close to the parabola, called a focus.
The same applies to our model: the first parabola reflects the waves emitted by an acoustic source placed in the focus making them parallel; the second concentrates them in the focus again. This makes it possible to hear even a very faint sound from a distance.