The Pitch and Loudness of Sound, and a Comparison of Audible Frequency Ranges

Objects that vibrate in some medium create mechanical waves known as sound waves, which propagate through that medium as vibrations of the individual molecules. If the sound wave enters the ear canal, it will eventually reach a thin membrane known as the eardrum, which will vibrate and in turn cause the three bones (malleus, incus, and stapes) to vibrate. This will ultimately send a signal to the brain and we will perceive the sound wave as sound. So sound is simply the way that humans and other animals perceive sound waves. Sound waves can propagate not only through air but also through other mediums such as steel, glass, helium and water. In air, the velocity of the sound waves depends on temperature and is given by an equation as described in the lecture. Whenever we describe sound waves, we usually mention the sound waves loudness and pitch. Loudness and pitch are subjective properties and depend on the intensity and frequency of the sound wave, respectively. The higher the intensity (power out put of the sound wave per unit area perpendicular to the movement of wave), the higher the loudness and the higher the frequency (number of complete oscillations per second), the higher the pitch. A good human ear is capable of detecting sound waves whose frequency ranges from twenty hertz to twenty thousand hertz. This range of frequency is known as the audible frequency range. A frequency above twenty thousand hertz is known as ultrasonic sound while a frequency below twenty hertz is known as infrasonic sound.


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