When we have two sounds whose frequencies differ little between each other, we perceive an extra sound, similar to the other two and with a sound that is similar to a beat whose rhythm is dictated by the the two main frequencies.
The human ear acts as a transducer of acoustic energy- firstly into mechanical energy and secondly into electric energy. Once the energy has been converted by the ear from the mechanical form into the electrical form, the electrical impulses reach the brain through nerve endings.
