When we hear sounds originating at a distance, we gather information concerning events at the distant location. From personal verbal communication carried by waves of sound, we make conclusions about what is in the mind of the speaker. “Listen to the sound of my voice” is an imperative beyond merely hearing sounds. The perception of vocal sound entails comprehension of the thought processes of the speaker. The pleasure of listening to music helps us understand the mind of the composer. As we work or walk, we translate the meaning of sounds we hear. We wonder, “What is the source of the sound? What message does the sound bring? How should I respond?” The impact of sound reception extends far beyond mere transfer of physical energy from its origin to its destination.
Of course we may not always consciously analyze the superabundance of sounds in this manner, but understanding the physical science of sound may provide a dimension of enjoyment we may otherwise miss. Most people do not think about what happens in the air when they carry on a conversation, listen to music, or hear the approach of a train. Sound is considered a “remote sense.” Humans are designed to be “remote sensors.” In recent years, remote sensing technology in military reconnaissance and radar navigation has become far more useful to society. Its application was, however, an extension of the senses gifted to living things. Higher animals share our ability to sense sound and sight remotely. In humans, however, the sense of sound helps us access the quality of soul and spirit in those fellow humans with whom we communicate at a deeper level.
Consider this very brief primer on sound. The human voice produces its sound with rapidly vibrating vocal cords. Instrumental music is produced by vibrating strings, reeds, drum heads, or air columns. Many other types of sounds are produced by various mechanical processes. Vibrating objects compress millions of discrete air molecules, pushing them together into a “pressure wave.” The air pressure in the wave may be only one millionth greater than the pressure before the compression took place. The pressure wave then rushes away at 1100 feet/sec, separated by a rarefaction, a region where the air pressure is slightly less, perhaps one millionth less than normal. For example, assume the pitch of a human voice is the same as Middle C on the piano. The vocal cord and the Middle C piano string produce 256 cycles/sec (pressure waves) separated by 256 rarefactions.
When we hear sounds of a voice or of music, we sense the arrival of pressure waves and rarefactions. Instruments measure how many pressure waves per second, also called cycles per second, or hertz, have been generated. The data do not begin to tell what happens when these pressure waves impact our body. We leave that story for future posts with a reminder that perceived pitch of the sound depends on the number of hertz, (cycles per sec (cps)) generated by the vibrating body. Our knowledge of physical sound and hearing are examples the Creator’s provision for highly efficient communication and information gathering among his created life forms.
Several 2008 posts dealt with principles of physical sound production in greater detail. They are a good introduction to a more extensive understanding of the sense of hearing:
