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.