The Physical Process Of Hearing

Kelvin Sholar

When we read basic musical literature, it is often assumed that the reader knows basic scientific terms for the properties of sound; especially relative to the physical process of hearing.

How do we hear sound and music?

The process of hearing begins with sound pressure waves. When I play the piano, I set the strings into motion which produces sound pressure waves that travel through the molecules of some medium. Normally, we hear the sound of the piano through air, but sound pressure waves can travels through solids (like the wall of a concert hall), or through a liquid (like the swimming pool at a pool party).

Sound pressure waves are funneled into the external ears – which we call the pinna when we talk in scientific terms. The ears funnel sound pressure waves into the external auditory canal, which ends with the eardrums. The scientific term for the eardrum is the membrana tympani. In this term, you might notice the word “tympani”, which is similar to the word timpani used to describe the percussion instrument in the orchestra. The eardrum is stretched over bone in the same way that the timpani’s skin is stretched over a metal frame.

The eardrum sends mechanical vibrations through the ossicle bones, the labyrinth and the middle ear muscles, into the cochlea. Once sound pressure waves reach the cochlea they stimulate the organ of Corti. This organ is a winding duct. It has nerve fibers of the spiral ganglion attached to it, and it separates the “scala vestibuli” and the “scala tympani”. Notice that the term timpani is used again here.

If the eardrum is moved by changes in sound pressure, then currents of electricity propagate (or move in other words) along nerves and the nervous system to the brain. When the currents of electricity reach the brain, the brain produces a psychological image – and that image is what we commonly call “sound” or “music”.